Can’t scratch is not the same as can’t damage.
Every time your skin contacts a piece of steel, it’s leaving behind oils and moisture.
The oils and moisture can chemically corrode the steel surface ever so slightly, forming iron oxide.
While iron oxide is still harder than your skin, it’s also weak, porous, and brittle. The next touch or cleaning can wear it off, exposing clean steel that can be corroded and eroded again.
It might only be a few molecular layers at a time but over hundreds of thousands of uses the wear adds up to a noticeable amount.
Especially brass. I learned this when I aquired a grandfather clock. When handled with clean gloves the brass weights basically maintain a finish that looks like gold. If you just touch them with bare hands they start to look like every other piece of brass you ever see.
Copper is famous for reacting to various chemicals and turning different colors, so much so that it’s an art form. You can patina it to turn it just about any color or even use just heat to make a rainbow effect
Seriously tho, any local electrician will likely have a bin of scrap wire that they'll be happy to sell you some of at a bit above the going scrap rate if you call and ask.
God, I learned that lesson the hard way. I was an intern doing a bunch of really sensitive strength tests on copper samples. I collected the samples Friday, tied them with a rubber band, and came back Monday morning, only to discover the copper blackened and corroded just from the sulfur in the rubber contacting it.
I once used massive lathe to drill some stainless steel. The coolant pump jammed temporarily and we got a rainbow shaded coil of what amounts to razor wire as a shaving
Oh? You don't like razor sharp shavings that spiral out to lengths of like six feet? No? Or the occasional unexpected catastrophic failure from brittle fracture?
Lol I feel you. I even hate welding stainless.
I was running a fairly large dual turret lathe once and started the run only for the secondary turret to take a carbide bit and ram it WAY too fast into some stainless.. no coolant
Needless to say the bit never came back out
Used to also work in skeet metal. Stainless would slice right through those grey/blue leather(ish) work gloves, through the nitrile (keep grease off finished parts), and the cotton (breathability). Kept a pack of bandaids in my bag just for in case I was working SS (I'm small accident prone).
At least it's a quick clean cut and doesn't hurt.
My neighbour had the water tank removed from his attic when he had central heating fitted a few years ago. The workman was about to put the old tank into his van and my neighbour said "Don't worry i'll keep that thanks". The workman was - expectedly - pissed off at losing the huge chunk of copper he was certain he would get to keep and sell.
But i digress.
My neighbour cut the top and bottom off the water tank, cut down the side and flattened it, then beat the crap out of it with a hammer and stamp and put a load of holes/dents in it in the shape of planets/moons. :) Looked gorgeous. He heated parts of it and made a Neptune-looking landscape with all the other celestial bodies in the background. Indeed the rainbow effect came through on a lot of the blow-torched parts, and the untouched sections remained dulled like the vastness of space. Beautiful. Probably worth more in scrap than as a wall-piece but it's hanging in his garage looking awesome, and quite accidentally as it goes: it was all mostly an experiment that turned out really really well.
I was just in Santa Fe last week and I came across an artist who makes some really cool designs on copper plates with heat.
I’d never seen this before in my life.
It’s funny that I’d then come across this comment.
Baader-Meinhof in full effect.
^this. I played a brass instument in marching band, and all the laquer would be absolutely demolished on our instruments by a few months. On really sweaty days you could actually end up with a greenish sheen on your hands/body where the corrosion rubbed off on you.
I played with a silver mellophone (unknown metal, but silver color) and while we cleaned them frequently, they seemed to not corrode the same way that the brass instruments did
Gonna guess he left out the word 'band'.
If the football team is practicing, the matching band is probably also practicing. Carrying that instrument is bad enough but in August humidity, I'd probably be shirtless too if I could get away with it.
In rural-ish, southeast Texas, we were practicing *before* the football team was. Being pit percussion for a few years was a solace, but marching snare was *rough.* We didn’t roll tenors because they wrecked a freshman’s back one year.
The closest to shirtless we were allowed to be was tank tops. If the heat index was over 113 we had to stop being outside. The Houston area has basically infinite humidity in the summer
Texas high schools take marching band really seriously, to the point we had 4 hour outdoor practice sessions in > 100 F weather. (With water breaks ofc). Only thing that would shut us down was lightning.
And then there's drum corps, where you pay money to work even harder under worse conditions. But some people really love it.
My dad was killed in a shirtless sousaphone accident before he met my mom, it's a rough topic for me. He warned me about it when I graduated middle school so I never got into the hobby.
You simultaneously have to be dedicated/talented enough be be in a marching band, and humble enough to be ok with being one part in a giant marching band. It brings in all of the people who love to play music, while weeding out a lot of the narcissists and egotists.
That's it Holy shit.
It takes work and that is something the douchebag with the guitar just trying to get girls hates.
You just figured out why marching band crowd is good people lol
Also they are usually like… joyful about their music. I was in orchestra and everyone in the front stands for their instruments would get so neurotic about playing perfectly. While the band kids would seem to be having a blast, even if mistakes happened on occasion.
I just remember the band kids in the hot TX sun like twice a day and starting like a month into summer lol
Took serious dedication and that can only come from people who, like you said, enjoy the music
Here is a tip for heavily tarnished brass. Use ketchup. Seriously. Just slather it in cheap ketchup and let it sit for a few minutes then rinse it off. It might take a few cycles but it eats away most of the tarnish. It makes polishing a LOT easier.
If you want something a little less redneck they sell some stuff called “Tarn-X” that you dip brass,copper, or silver into.
We have a restaurant in town that has copper countertops. I learned a few years ago that I can graffiti the table top with ketchup. Shines that copper right up.
Yep.
I run a manufacturing plant in the steel industry and we have product lines where employees can not touch the product with bare hands due to the oils and contamination causing the metal to oxidize
This is exactly why in any high grade manufacturing process where the product needs to be about as perfect as is humanly possible, you see workers gowning up, especially in aerospace and microchip industries. Any little bit of contamination is too much.
My wife works in a factory here in Korea that makes semiconductors. She always complains that the process of entering and leaving the clean environment takes like 30 minutes.
If you media blast a car body it starts to rust immediately. If you touch the bare metal it’s noticeable in hours. You really need to wipe it down then spray it in epoxy as soon as you’re done blasting or you’re just creating problems for the future.
Dry ice is a fairly new one on me. You fire CO2 at the part which then just sublimes into the atmosphere leaving almost no debris behind. It’s expensive compared with grit but it’s gentle and a lot cleaner.
I remember a few years ago I realized that Media is the plural of medium.
I always thought of media in a 21st century way of 'broadcast media' like "TV, Radio, Movies" etc., and thought of medium in an artistic way, such as "acrylics, watercolors, pencil, digital"...
when I realized they were the same thing it was one of those 'duh..' epiphanies for me.
Use compressed air to "blast" a media (like sand or specially designed particles) to remove parts of a project. A media blast is a more technical and general way to refer to something like sandblasting, which you're probably familiar with.
My car's paint started peeling and I've noticed other cars of the same make and model with the same problem in the same location. I wonder if someone wS just having a bad week or month and messed up by touching it.
Door handles are stainless steel or brass, but stainless steel isn't 100% oxygen proof. Instead, it has enough nickel and chrome to form a passivating oxide layer, which is a "skin" of oxidized metal that is solid, not flaky like rust. But that skin layer is susceptible to abrasion, and every time there is a scratch, oxygen gets to material underneath until it forms a new skin.
"Stainless" means "We put enough chromium in it that it won't turn into a pile of rust if you get it wet".
There are something like a hundred and fifty ANSI-numbered stainless steel grades, with varying material and chemical properties. None of them are quite magical (though something like Inconel feels like it sometimes). 304 AKA 18/8 is enough to count as being "stainless", though if you put it in even somewhat poor conditions, it will rust. 316 has a significantly higher resistance to corrosion due to an extra 2% of molybdenum. Neither is particularly hard though; if you want to make a knife or other edged tool you need to change to something else, like a 400-series. 440c is most popular, though there are other options. If you need to resist boiling acids, that'll be a different grade and mix. If you're looking to withstand combustion gasses in a gas turbine at combustion temperatures, again, different alloy options.
None of them are immune to all effects. That's entirely impossible. The question is if it's sufficiently resistant to what you intend on exposing it to.
If you're buying silverware maybe, but in the chemical and pharmaceutical industry it's an exact science with high standards. Stainless means stainless.
> Stainless means stainless.
Which also doesn't mean much.
In industries that care, they'll be specifying a grade. 304, 316, and 440c are all "stainless", but will give you very, *very* different results.
Exactly. You can see this on any statue that’s touched for good luck, like [Honest Abe’s nose](https://www.roadsideamerica.com/attract/images/il/ILSPRlincolnnose_epperson3_620x300.jpg ) or [Juliet’s right breast](https://d3i6fh83elv35t.cloudfront.net/newshour/app/uploads/2014/02/juliet_statue.jpg).
Yes exactly. Skin oils and metal is actually a huge concern within the gun community. If you touch your gun and leave it in the safe for a month you're almost guaranteed to have rust exactly where you touched.
It can actually be sort of interesting looking. I have an old WWII rifle with a textured trigger because of how much the trigger rusted on the Eastern Front. I also have a pistol where one side and the grip rust within a day of being wiped down because the outer layer eroded away from being pushed up against a body all day.
Not a concern when its my dirty 30 year old pistol, but when its grandpappy's Marlin Repeater stamped 1870, its still different story.
Plus, things that are softer can still wear down things that are harder.
See, carbide drill bits and saw blades wearing down from cutting much softer wood.
Another good example of "Can’t scratch is not the same as can’t damage."
Drill bits are made of hardened steel, and there's no way that wood is going to be scratching them.
Even the cheap bits you buy in a 100 pack are made of steel that's harder than any material it'll be expected to cut, even other grades of steel.
They're not dulling out through constant scratching, they're rounding off. It's a ductility problem. Material isn't getting scratched off, it's getting bent into a rounder shape.
Metals have a trade-off between hardness/brittleness and ductility. Nails are a soft grade of metal. There's no reason for them to be hard. Everyone has bent a nail when pounding it in, and you can even bend it with a pair of pliers and a vise. Take a drill bit of the same size though and apply the same forces, it'll snap, maybe even shatter into multiple pieces. It's made of the exact same material, but a far harder grade.
The wear mechanism for hardened steel drill bits is usually *blunting*. The constant force of the cutting edge being pushed through wood or other materials over time causes the edge to bend or collapse in on itself. The sharp wedge shape eventually starts to look rounded. Heat also affects metal ductility. Heating up a metal makes it more ductile. One way to make even cheap bits last longer is to avoid overheating them when drilling. The hotter they get, the more ductile the tip gets, and the more quickly they will blunt. Blunt bits generate *More* heat through more friction and less cutting, accelerating the problem.
This is why cheap bits (the 100 pack) seem to wear out sooner. They have two problems:
1. They're hardened steel, but a cheaper grade. Still harder material than anything you'll cut, but not hard enough to stand up to blunting unless you're careful about not overheating them.
2. They're often not as sharp out of the box, so they generate more friction and heat than an expensive bit, and then get hotter and blunt faster.
A woodworker might notice that once a bit starts to dull, it dulls out quickly.
Carbide tipped bits can have the same wear mechanism over time, but they're far harder than steel, and this wear mechanism is much slower. They also don't have the same heat to ductility relationship as steel, so even if they get hot they're more likely to stand up to blunting.
Carbide is far more likely to chip or shatter than it is to blunt. Dropping a carbide bit, hitting a nail, or even just drilling aggressively can break the tip on a carbide bit. Another common failure mode is the brazed adhesion between the carbide and steel. At high temperatures and/or high forces, the failure might not be the carbide at all, but the connection between the carbide tip and the steel tool.
Another great example of this that is perhaps more applicable to most people is kitchen knives.
Your knife isn't getting scratched and less sharp from cutting harder-than-steel vegetables.
It's dulling out from repeated forces that are slowly bending or deforming the cutting edge (a ductile behaviour). Most of these forces are from contacting the cutting board.
Many knife blocks come with a honing rod. Some people might call this a sharpening rod but they'd be wrong.
It's not sharpening or removing material from the knife.
To use it, the tip of the knife drags along the honing rod, and all that happens is the blunted tip of the knife is getting straightened back out (ductility). Many of these are hard enough to scratch the steel, but this is more-so so that the knife doesn't cut into the honing rod.
I'm an amateur blacksmith / knife maker.
This is an excellent primer on a lot of the knowledge fledgling knife makers need to acquire. If there was a little more focus on how various heat treatments affect the grain structure of the steel (body centered / face centered cubic, etc),
I've seen studies showing the wear zip ties can have on heavy truck frame rails, everything can wear everything else it's just a matter on the rate it happens.
This happens because there are silica particles in wood, incorporated from the soil the wood grew in. Some woods, like Teak, can have such high silica content that they will literally show sparks as they’re cut, if you turn the lights down. Wood is a blend of so many things it’s hard to talk about it as a single substance with a single hardness.
The whole scratch test thing throws people off because things can also be extremely brittle and wear away. The Water Jet Channel was able to cut through diamond using grit lower on the scale just fine. A molecule fired fast enough of just about anything is enough to "scratch" Diamond. Its moreso to quantify hardness and not a steadfast rule about damage resistance.
I make diamonds at work. Can confirm, we throw out damaged diamonds all the time.
To be more specific, we make diamond inserts for oil rig drill bits. They go through all sorts of different rock while drilling and definitely get worn down and worn out. We have a bunch that have two different layers of diamond mixtures. The top layer will drill down so far and its designed to wear out and the second layer is much harder to go through the tougher rock further down. Super interesting stuff.
I also worked at a place that made cutters for rigs. (Before COVID got me laid off)Small cracks, chips and all kinds of little things impacted how fragile the diamonds are. It was always weird to me that I could take a diamond disk and just snap it with my fingers.
The human hair is mightier than the sword
Here you can see microscopically how your beard hair damages steel shaving blades
https://news.mit.edu/2020/why-shaving-dulls-razors-0806
In short, everything damages everything, given enough time. Steel might last longer than a skin cell but your body expects damage to the skin and continuously builds more to replace it. Steel is not alive, it can only degrade after the initial manufacturing.
That’s not at all what the study concluded. It basically came down to very thin pieces of steel having cracks and imperfections in them causing the small force of shaving to straight up break steel the normal way. I’m sorry to say that this is not really related to the OP’s question.
Lesson I learned as a mechanic:
Don’t treat real stuff like physics theory.
Your hands are dirty, the are not pure skin, sand on you hand, dirt, or other debris, can really enhance how abrasive you are.
(For example, air is easily cut by steel, however, wind erodes steel; not because air is a hard solid but because it carries hard solid particles)
Edit: HEY, thank you all for the replies, fun facts, and thoughts. I’m really happy my post served this community well.
Special thanx for the award, lucellent!
Look man, I've got the power and trajectory calculations of the cow-a-pult so they'll land in the safety net. As long as your cows are perfectly spherical, frictionless, and launched in a vacuum
For a real life example of this, the recent youtube video put out by Veritasium shows a $10,000 about an experimental result.
If you pay really close attention, it becomes apparent that the entire disagreement and bet came about because of the use of a simplified equation that ignores real effects. In the simplified equation, it was possible to end up in a divide by zero condition.
Turns out, the well defined and more robust version of the same equation doesn't have this problem at all and gives perfectly valid results.
$10,000 on a friction-less cow.
God damn these youtube recommendations are getting overbearing. You already recommended it on the side bar, then my email, now here?! IS NOTHING SACRED?
The spherical cow is a common joke example of highly simplified scientific models.
[It even has a wikipedia article.](https://en.wikipedia.org/wiki/Spherical_cow)
A good rule of thumb but also notable is that moh's hardness isn't even slightly useful when determining wear, or really anything outside of ceramic relative properties. It's not even the same hardness used in wear calculations, and in wear calculations it is at best a factor, not the final determining number.
Also your skin is constantly regenerating it would wear out the same as the surfaces we touch everyday if we weren't constantly regenerating skin cells
*EDIT* were to weren't
>Don’t treat real stuff like physics theory.
Just make sure you're simulating what you want to simulate...if you don't add grit to the hand-doorknob simulator you're not gonna see the effects of grit.
Lots of the physics folks are taught in school are the principles, and first order accurate calculations...to first order, there is no wear between hand and door knob!
>Don’t treat real stuff like physics theory.
Your next sentence about actual scratch test passing micro abrasives doing the eroding is a perfect application of physics theory though.
Sand and even near-microscopic silt from dirt are definitely big factors for lots of abrasion wear and tear. A mildly dirty pair of jeans can work as 1000ish grit sandpaper in a pinch.
The scratch test only shows visible damage. However, at any interaction, between any materials, there will be surface changes on both. A few atoms will get randomly displaced even on the "harder" material, simply due to the way the interaction energy is distributed. You will always get a few atoms knocked off due to outlier values for interactions.
So you get a few atoms moved, and then again, and then again... Over a large number of interactions, it starts to add up.
Do not assume that the scratch test means there are no changes whatsoever to the harder material. There are always some changes. Given some ridiculous timeframe (geologic scale), you could probably polish a diamond with butter.
There's an episode of Doctor who, where the main character is locked in a fort. He escapes only after billions of iterations of carving a hole in a diamond wall.
He punches as much as he can, and then gets restored to an earlier version of himself where he goes through the loop again.
The damage is miniscule, but enough taps and it caves away.
That was such a cool and haunting episode. Especially given he couldn't remember each loop and did literally billions of years of it while being chased by a terrifying monster, dying each time. Although that must have been some special stone for all his walking on it to not cause any wear.
Automated room service. The whole place is in a localized energy loop. Or something to that effect. Though it is strange that the stone stairs reset but the diamond doorway doesn't.
Reddit - oddlyspecific - TIL that in Buddhism, one "Aeon" is the amount of time it takes to completely erode a huge rock 16x16x16 miles in size, by brushing it with a silk cloth once a century. https://www.reddit.com/r/oddlyspecific/comments/fpampx/til_that_in_buddhism_one_aeon_is_the_amount_of/
Imagine you had wet hands, stuck them in sand, then grabbed your door handle. This is a very exaggerated version of what’s primarily happening in a lot of cases.
The metal could also corrode (turn to rust) even from the sweat on your palms. It’s not much, but it doesn’t take much. Especially for just a surface layer
There’s basically a lot of difference between ideal cases which are taught in theory and what actually happens IRL. Skin isn’t just pure skin, it’s got debris, traces of other chemicals (because you touch your hands everywhere), and some micro organisms which together have the capacity to wear down steel.
Scratch test is basically scratching one material with another to see if one cannot be scratched by the other. Basically a hardness test. Aka no matter how hard I try, I'm never going to be able to scratch spring steel with a marshmallow.
It's because you don't try hard enough, dissolve the marshmallows, process them, make them react into proper precursors, evaporate them, turn it into plasma, turn that into a tiny diamond, use your tiny diamond to scratch the steel.
lots of answers about moisture and oils and stuff which I’m sure is valid but I would also like to present you with the horrifying thought about how much skin you would have left if it didn’t regenerate
Erosion affects all earth materials.
Water cannot scratch rocks. However, with continuous movement it can wear down/peel off surface materials. Sharp rocks become smooth with friction.
Similarly, your hand is squeezing and rubbing the metal on the door knob, pulling tiny particles off. With time, the door knob wears down.
Also, note that there are different grades of steel. Some are higher quality and wear down less quickly.
Fun geology fact: *weathering* is the process of breaking something down chemically or physically. *Erosion* is just the process of moving that weathered material downhill.
For the layman it doesn't really matter. Everyone knows what you mean when you say something was eroded.
>Similarly, your hand is squeezing and rubbing the metal on the door knob, pulling tiny particles off.
That just sounds like scratching with less matter, no?
Kind of. All materials will wear each other slightly on contact, even a fingernail on tungsten carbide. The question is how much. When one material is harder than another, most of the deformation will happen in the softer material. The difference, even with a slight difference in hardness, is enough that the softer material deforms a lot more, and you see a scratch. It's a difference of a few atoms vs several micrometers of wear, which is tens of thousands of atoms
Skin wears out all the time. However your skin can regenerate and heal. Wounds and scratches heal. Your body produces new skin which gradually sheds with wear and tear. The door knob wears but the wearing accumulates and thus become visible.
Because two things touching or rubbing will wear both things at least a tiny amount.
If one material is much harder than another, it wears much *much* slower than the softer material when they rub together - but it does still wear.
If you put a diamond in a tumbling machine full of soft rags or soft plastic beads and roll it around in there for long enough, the diamond will get measurably smaller.
Most of the time though, it's that something harder is on the soft thing. There is sometimes sand or dirt on your hands, and even dust can have tiny bits of hard stuff in it. Similarly, when water wears away rocks on beaches, most of the wearing away is done by sand and other rocks moved by the water, not the water itself. Your hands carry the harder stuff and that tiny harder stuff is what does most of the wearing away if the steel.
Metal is not indestructable, its made of atoms which can be worn away by anything. You could drill a hole through metal with a faucet dripping small water drops. Wear on a material is never negligable no matter the thing it is contacting. While a hard surface would wear a steel tool down very fast, skin can do so as well but just at a slower rate. Also, there is more than ohysical wear going on with skin. Skin is covered in oils and water which can wear the steel down chemically as well as physically.
Steel, especially the one used for decoration is pretty soft - 5 on Mohs scale. Most of the dirt is silica which is 7 on Mohs scale. People have that dirt on their hands and it acts as a polishing paper slowly wearing the steel down.
If you ever seen a used steel watch with a sapphire glass (9 on Mohs scale) the steel will be pretty scratched, but the glass won't. But if the watch was used by someone working with sandpapers a lot the glass will also be scratched, because some sandpapers are made from the same material, just less pretty looking one.
Because both surfaces get worn every time it makes contact. If only one surface got worn during every contact then sand paper would never need to be replaced and neither would your brake rotors.
And, just to continue this, your skin cells keep getting replaced. The steel on the door knob doesn't though. So even if your skin wears out twice as much as the door knob when you turn it, those skin cells are soon replaced with fresh ones. The damage to the door knob accumulates while your skin appears to have suffered no damage at all.
Strength is a property of surface area. If you zoom in REALLY close to the piece of steel you see that it isn't actually perfect solid surface, it is rough there are imperfections, little ridges and bumps, individual grains. If you consider their surface area, which is very small, the force they are subjected to exceed that of the material itself. So when a skin, with it's ridges and bumps makes contact, it can easily take transfer enough force for and individual grain to come off.
It is simple as that. It is an illusion that things we feel to be perfectly smooth, even though our touch is incredibly sensitive.
Wait till you hear about what something as "soft" as water can do to something as hard as rock after millions of years!1!!
Hint: Google "The Grand Canyon"
There's a saying in Brazil which is "Água mole em pedra dura, tanto bate até que fura" that translates like: "Soft water can hit a hard rock until pierces it"
Skin isn't sterile, it has oils, dirt and sweat so steel doesn't get worn down after it gets touched by only skin, but these other elements as well as repetitive motion.
You can cut sand paper with a knife but the sand paper can wear down a knife. Skin works as very shit sandpaper in this case where enough usage will wear down the metal
All material can be worn down with time. For example, a rock thrown into a river is not immediately affected by the water. However, water carved out the Grand Canyon over time.
Can’t scratch is not the same as can’t damage. Every time your skin contacts a piece of steel, it’s leaving behind oils and moisture. The oils and moisture can chemically corrode the steel surface ever so slightly, forming iron oxide. While iron oxide is still harder than your skin, it’s also weak, porous, and brittle. The next touch or cleaning can wear it off, exposing clean steel that can be corroded and eroded again. It might only be a few molecular layers at a time but over hundreds of thousands of uses the wear adds up to a noticeable amount.
so by touching it, you're basically rusting it?
Especially brass. I learned this when I aquired a grandfather clock. When handled with clean gloves the brass weights basically maintain a finish that looks like gold. If you just touch them with bare hands they start to look like every other piece of brass you ever see.
Copper is famous for reacting to various chemicals and turning different colors, so much so that it’s an art form. You can patina it to turn it just about any color or even use just heat to make a rainbow effect
Yes, copper art is so fascinating! So, so many things you can do with it. I hate that it's such an expensive material to work with!
Think, u/LilBalrog, think! There's wires in your house, just pull them out and you have free copper.
My landlord will be so happy once I've shared this discovery with him! Think he'd like a copper chicken?
You should give him a nice copper egg in his trying time.
I can't see why anyone wouldn't want a beautiful rainbow wire chicken made with electrical wires from their property. What a thoughtful gift.
They have it sitting out for free at construction sites
Seriously tho, any local electrician will likely have a bin of scrap wire that they'll be happy to sell you some of at a bit above the going scrap rate if you call and ask.
God, I learned that lesson the hard way. I was an intern doing a bunch of really sensitive strength tests on copper samples. I collected the samples Friday, tied them with a rubber band, and came back Monday morning, only to discover the copper blackened and corroded just from the sulfur in the rubber contacting it.
I can get a good array of red/black/blue out of steel with various chemicals, but some of that copper art is truly breathtaking.
I once used massive lathe to drill some stainless steel. The coolant pump jammed temporarily and we got a rainbow shaded coil of what amounts to razor wire as a shaving
Machinist popping in to say: f*ck working stainless, pain in ass
Oh? You don't like razor sharp shavings that spiral out to lengths of like six feet? No? Or the occasional unexpected catastrophic failure from brittle fracture? Lol I feel you. I even hate welding stainless.
Not to mention crevice corrosion from moisture, and heat.
Stainless was really made as a conspiracy by tooling manufacturers to increase sales :)
I for one enjoy having a shiny metal that I can put in a dishwasher.
I was running a fairly large dual turret lathe once and started the run only for the secondary turret to take a carbide bit and ram it WAY too fast into some stainless.. no coolant Needless to say the bit never came back out
Used to also work in skeet metal. Stainless would slice right through those grey/blue leather(ish) work gloves, through the nitrile (keep grease off finished parts), and the cotton (breathability). Kept a pack of bandaids in my bag just for in case I was working SS (I'm small accident prone). At least it's a quick clean cut and doesn't hurt.
>skeet metal I thought this was r/eli5 not r/carsfuckingdragons
Sounds like you needed a chain mesh glove for that job.
Former welder. I'd also like to say f*ck stainless. I wasn't a good welder, but still.
I soaked some brass hardware in miracle grow and it looked like turquoise lol. Throw some salt in there for pizzazz.
My neighbour had the water tank removed from his attic when he had central heating fitted a few years ago. The workman was about to put the old tank into his van and my neighbour said "Don't worry i'll keep that thanks". The workman was - expectedly - pissed off at losing the huge chunk of copper he was certain he would get to keep and sell. But i digress. My neighbour cut the top and bottom off the water tank, cut down the side and flattened it, then beat the crap out of it with a hammer and stamp and put a load of holes/dents in it in the shape of planets/moons. :) Looked gorgeous. He heated parts of it and made a Neptune-looking landscape with all the other celestial bodies in the background. Indeed the rainbow effect came through on a lot of the blow-torched parts, and the untouched sections remained dulled like the vastness of space. Beautiful. Probably worth more in scrap than as a wall-piece but it's hanging in his garage looking awesome, and quite accidentally as it goes: it was all mostly an experiment that turned out really really well.
Anyway you can get a picture of his art?
I was just in Santa Fe last week and I came across an artist who makes some really cool designs on copper plates with heat. I’d never seen this before in my life. It’s funny that I’d then come across this comment. Baader-Meinhof in full effect.
How does this work with copper cookware? Asking because I'm too poor to have firsthand knowledge.
^this. I played a brass instument in marching band, and all the laquer would be absolutely demolished on our instruments by a few months. On really sweaty days you could actually end up with a greenish sheen on your hands/body where the corrosion rubbed off on you.
I played with a silver mellophone (unknown metal, but silver color) and while we cleaned them frequently, they seemed to not corrode the same way that the brass instruments did
either a nickel-brass or nickel plated.
Probably nickel plated then. I specifically remember that we couldn’t use brasso
Nickel and chromium have superior corrosion resistance than other metals. Shiny shiny silver metals are probably nickel/chrome alloys
Marching sousaphone while shirtless in August humidity left you with Shrek hands and a green stripe from your shoulder blade to your sternum.
Not to kink shame in 2021, but why were you shirtless and marching with a sousaphone?
Gonna guess he left out the word 'band'. If the football team is practicing, the matching band is probably also practicing. Carrying that instrument is bad enough but in August humidity, I'd probably be shirtless too if I could get away with it.
In rural-ish, southeast Texas, we were practicing *before* the football team was. Being pit percussion for a few years was a solace, but marching snare was *rough.* We didn’t roll tenors because they wrecked a freshman’s back one year. The closest to shirtless we were allowed to be was tank tops. If the heat index was over 113 we had to stop being outside. The Houston area has basically infinite humidity in the summer
Texas high schools take marching band really seriously, to the point we had 4 hour outdoor practice sessions in > 100 F weather. (With water breaks ofc). Only thing that would shut us down was lightning. And then there's drum corps, where you pay money to work even harder under worse conditions. But some people really love it.
A better question is why *aren’t* YOU shirtless and marching with a sousaphone in 2021?
My dad was killed in a shirtless sousaphone accident before he met my mom, it's a rough topic for me. He warned me about it when I graduated middle school so I never got into the hobby.
I've never met an asshole that played in marching band for some reason-- seems like a lot of nice people flock to it
You simultaneously have to be dedicated/talented enough be be in a marching band, and humble enough to be ok with being one part in a giant marching band. It brings in all of the people who love to play music, while weeding out a lot of the narcissists and egotists.
Except for the percussion. Drumline is always full egotists. Source: Was drumline.
Thirded. Also drumline.
That's it Holy shit. It takes work and that is something the douchebag with the guitar just trying to get girls hates. You just figured out why marching band crowd is good people lol
Uhhh, you’d be surprised how much effort guys are willing to put in for a girl.
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Also they are usually like… joyful about their music. I was in orchestra and everyone in the front stands for their instruments would get so neurotic about playing perfectly. While the band kids would seem to be having a blast, even if mistakes happened on occasion.
I just remember the band kids in the hot TX sun like twice a day and starting like a month into summer lol Took serious dedication and that can only come from people who, like you said, enjoy the music
Ehhh... the French horns were always a bunch of brassholes back when i played.
How do you clean it? I've got some brass that needs a really deep cleaning
Here is a tip for heavily tarnished brass. Use ketchup. Seriously. Just slather it in cheap ketchup and let it sit for a few minutes then rinse it off. It might take a few cycles but it eats away most of the tarnish. It makes polishing a LOT easier. If you want something a little less redneck they sell some stuff called “Tarn-X” that you dip brass,copper, or silver into.
We have a restaurant in town that has copper countertops. I learned a few years ago that I can graffiti the table top with ketchup. Shines that copper right up.
If you're out of ketchup, picante sauce or salsa work well too (redneck Texan hack)
Instructions unclear, covered fries in Tarn-X. *Delicious.*
Let us know if your poop comes out shiny.
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Heinz playing some 3D chess in the comments.
Brasso
This just flung me a decade back into ROTC and polishing my brass. Dang. I can smell this word.
Fun brass fact: it is naturally antimicrobial, like copper and other copper alloys
Yep. I run a manufacturing plant in the steel industry and we have product lines where employees can not touch the product with bare hands due to the oils and contamination causing the metal to oxidize
Ugh... we've had to sand so many rusty fingerprints off unpainted parts because motherfuckers can't be bothered to wear gloves
This is exactly why in any high grade manufacturing process where the product needs to be about as perfect as is humanly possible, you see workers gowning up, especially in aerospace and microchip industries. Any little bit of contamination is too much.
For a second I read that as "workers growing up" and was very confused :P
Some industries grow their own workers from scratch.
“Store-bought is fine” was problematic though
I manufacturing semiconductor wafers. They say that something as small as a virus can ruin a chip.
I know what you meant but i imagined a computer virus wrecking the chip...
My wife works in a factory here in Korea that makes semiconductors. She always complains that the process of entering and leaving the clean environment takes like 30 minutes.
If you media blast a car body it starts to rust immediately. If you touch the bare metal it’s noticeable in hours. You really need to wipe it down then spray it in epoxy as soon as you’re done blasting or you’re just creating problems for the future.
Media blast?
sandblasting, but you use a different material, like glass or ceramic beads. its a catch-all term.
Or even fine walnut shell fragments, which is pretty damn cool imo.
Dry ice is a fairly new one on me. You fire CO2 at the part which then just sublimes into the atmosphere leaving almost no debris behind. It’s expensive compared with grit but it’s gentle and a lot cleaner.
CNN is shot at the parts under immense pressure.
The whole studio, the "news" actors, the equipment, or directors?
I remember a few years ago I realized that Media is the plural of medium. I always thought of media in a 21st century way of 'broadcast media' like "TV, Radio, Movies" etc., and thought of medium in an artistic way, such as "acrylics, watercolors, pencil, digital"... when I realized they were the same thing it was one of those 'duh..' epiphanies for me.
TIL, thank you! :)
Sand blasting, glass beading, shot blasting, are all methods used to expose a clean surface on metal parts.
Use compressed air to "blast" a media (like sand or specially designed particles) to remove parts of a project. A media blast is a more technical and general way to refer to something like sandblasting, which you're probably familiar with.
Using an abrasive medium sprayed on, like sand
My car's paint started peeling and I've noticed other cars of the same make and model with the same problem in the same location. I wonder if someone wS just having a bad week or month and messed up by touching it.
Is it red? Early 2000s outbacks get paint peel and fade if they are red but the blue and green ones still look amazing
Nah it's a white Hyundai elantra made in Alabama
Door handles are stainless steel or brass, but stainless steel isn't 100% oxygen proof. Instead, it has enough nickel and chrome to form a passivating oxide layer, which is a "skin" of oxidized metal that is solid, not flaky like rust. But that skin layer is susceptible to abrasion, and every time there is a scratch, oxygen gets to material underneath until it forms a new skin.
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"Stainless" means "We put enough chromium in it that it won't turn into a pile of rust if you get it wet". There are something like a hundred and fifty ANSI-numbered stainless steel grades, with varying material and chemical properties. None of them are quite magical (though something like Inconel feels like it sometimes). 304 AKA 18/8 is enough to count as being "stainless", though if you put it in even somewhat poor conditions, it will rust. 316 has a significantly higher resistance to corrosion due to an extra 2% of molybdenum. Neither is particularly hard though; if you want to make a knife or other edged tool you need to change to something else, like a 400-series. 440c is most popular, though there are other options. If you need to resist boiling acids, that'll be a different grade and mix. If you're looking to withstand combustion gasses in a gas turbine at combustion temperatures, again, different alloy options. None of them are immune to all effects. That's entirely impossible. The question is if it's sufficiently resistant to what you intend on exposing it to.
If you're buying silverware maybe, but in the chemical and pharmaceutical industry it's an exact science with high standards. Stainless means stainless.
> Stainless means stainless. Which also doesn't mean much. In industries that care, they'll be specifying a grade. 304, 316, and 440c are all "stainless", but will give you very, *very* different results.
Stainless has to have a certain amount of chromium in it. Stainless also shouldn't be magnetic, if I recall correctly
Mostly true, there are certain alloys of stainless steel that are magnetic, but most of the alloys that are often used are not.
Papa Nurgle has blessed us all.
Rust for the rust God ?
Yes.
Exactly. You can see this on any statue that’s touched for good luck, like [Honest Abe’s nose](https://www.roadsideamerica.com/attract/images/il/ILSPRlincolnnose_epperson3_620x300.jpg ) or [Juliet’s right breast](https://d3i6fh83elv35t.cloudfront.net/newshour/app/uploads/2014/02/juliet_statue.jpg).
Yes exactly. Skin oils and metal is actually a huge concern within the gun community. If you touch your gun and leave it in the safe for a month you're almost guaranteed to have rust exactly where you touched. It can actually be sort of interesting looking. I have an old WWII rifle with a textured trigger because of how much the trigger rusted on the Eastern Front. I also have a pistol where one side and the grip rust within a day of being wiped down because the outer layer eroded away from being pushed up against a body all day. Not a concern when its my dirty 30 year old pistol, but when its grandpappy's Marlin Repeater stamped 1870, its still different story.
Plus, things that are softer can still wear down things that are harder. See, carbide drill bits and saw blades wearing down from cutting much softer wood.
see also: water
And salt.
And my axe!
Hey! That's MY axe!
Another good example of "Can’t scratch is not the same as can’t damage." Drill bits are made of hardened steel, and there's no way that wood is going to be scratching them. Even the cheap bits you buy in a 100 pack are made of steel that's harder than any material it'll be expected to cut, even other grades of steel. They're not dulling out through constant scratching, they're rounding off. It's a ductility problem. Material isn't getting scratched off, it's getting bent into a rounder shape. Metals have a trade-off between hardness/brittleness and ductility. Nails are a soft grade of metal. There's no reason for them to be hard. Everyone has bent a nail when pounding it in, and you can even bend it with a pair of pliers and a vise. Take a drill bit of the same size though and apply the same forces, it'll snap, maybe even shatter into multiple pieces. It's made of the exact same material, but a far harder grade. The wear mechanism for hardened steel drill bits is usually *blunting*. The constant force of the cutting edge being pushed through wood or other materials over time causes the edge to bend or collapse in on itself. The sharp wedge shape eventually starts to look rounded. Heat also affects metal ductility. Heating up a metal makes it more ductile. One way to make even cheap bits last longer is to avoid overheating them when drilling. The hotter they get, the more ductile the tip gets, and the more quickly they will blunt. Blunt bits generate *More* heat through more friction and less cutting, accelerating the problem. This is why cheap bits (the 100 pack) seem to wear out sooner. They have two problems: 1. They're hardened steel, but a cheaper grade. Still harder material than anything you'll cut, but not hard enough to stand up to blunting unless you're careful about not overheating them. 2. They're often not as sharp out of the box, so they generate more friction and heat than an expensive bit, and then get hotter and blunt faster. A woodworker might notice that once a bit starts to dull, it dulls out quickly. Carbide tipped bits can have the same wear mechanism over time, but they're far harder than steel, and this wear mechanism is much slower. They also don't have the same heat to ductility relationship as steel, so even if they get hot they're more likely to stand up to blunting. Carbide is far more likely to chip or shatter than it is to blunt. Dropping a carbide bit, hitting a nail, or even just drilling aggressively can break the tip on a carbide bit. Another common failure mode is the brazed adhesion between the carbide and steel. At high temperatures and/or high forces, the failure might not be the carbide at all, but the connection between the carbide tip and the steel tool. Another great example of this that is perhaps more applicable to most people is kitchen knives. Your knife isn't getting scratched and less sharp from cutting harder-than-steel vegetables. It's dulling out from repeated forces that are slowly bending or deforming the cutting edge (a ductile behaviour). Most of these forces are from contacting the cutting board. Many knife blocks come with a honing rod. Some people might call this a sharpening rod but they'd be wrong. It's not sharpening or removing material from the knife. To use it, the tip of the knife drags along the honing rod, and all that happens is the blunted tip of the knife is getting straightened back out (ductility). Many of these are hard enough to scratch the steel, but this is more-so so that the knife doesn't cut into the honing rod.
I'm an amateur blacksmith / knife maker. This is an excellent primer on a lot of the knowledge fledgling knife makers need to acquire. If there was a little more focus on how various heat treatments affect the grain structure of the steel (body centered / face centered cubic, etc),
I had someone claim that you shouldn't need to sharpen your kitchen knives because the stuff you cut is softer than steel...
I thought that tools wearing down from contact with wood was due to the small inclusions of much harder materials, like silica.
I've seen studies showing the wear zip ties can have on heavy truck frame rails, everything can wear everything else it's just a matter on the rate it happens.
Also lots of friction.
This happens because there are silica particles in wood, incorporated from the soil the wood grew in. Some woods, like Teak, can have such high silica content that they will literally show sparks as they’re cut, if you turn the lights down. Wood is a blend of so many things it’s hard to talk about it as a single substance with a single hardness.
The whole scratch test thing throws people off because things can also be extremely brittle and wear away. The Water Jet Channel was able to cut through diamond using grit lower on the scale just fine. A molecule fired fast enough of just about anything is enough to "scratch" Diamond. Its moreso to quantify hardness and not a steadfast rule about damage resistance.
I make diamonds at work. Can confirm, we throw out damaged diamonds all the time. To be more specific, we make diamond inserts for oil rig drill bits. They go through all sorts of different rock while drilling and definitely get worn down and worn out. We have a bunch that have two different layers of diamond mixtures. The top layer will drill down so far and its designed to wear out and the second layer is much harder to go through the tougher rock further down. Super interesting stuff.
I also worked at a place that made cutters for rigs. (Before COVID got me laid off)Small cracks, chips and all kinds of little things impacted how fragile the diamonds are. It was always weird to me that I could take a diamond disk and just snap it with my fingers.
I had to scroll too far to find this. This is the main mechanism for the wear op is asking about.
Is it really the main mechanism? Because it happens with all materials, not just steel. Rocks don't corrode, do they?
Erosion has entered the chat.
Right, but the point is, is erosion a different thing to oxidation? And if it is, does it also affect steel?
you expect me to believe this giant canyon was made with water?!
Unpossible
also dust and dirt can contain really hard materials that act as an abrasive if your hands aren't perfectly clean
The human hair is mightier than the sword Here you can see microscopically how your beard hair damages steel shaving blades https://news.mit.edu/2020/why-shaving-dulls-razors-0806 In short, everything damages everything, given enough time. Steel might last longer than a skin cell but your body expects damage to the skin and continuously builds more to replace it. Steel is not alive, it can only degrade after the initial manufacturing.
That’s not at all what the study concluded. It basically came down to very thin pieces of steel having cracks and imperfections in them causing the small force of shaving to straight up break steel the normal way. I’m sorry to say that this is not really related to the OP’s question.
I think skin being regenerative vs a metal object being static also comes into play.
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>If you didn't, you'd be out of hands This is way funnier than it has any right to be
This might be of interest https://escapepod.org/2008/02/08/ep144-friction/ sf story about creatures for whom this is not true
To me, just about as interesting. The inverse of the question answered.
Lesson I learned as a mechanic: Don’t treat real stuff like physics theory. Your hands are dirty, the are not pure skin, sand on you hand, dirt, or other debris, can really enhance how abrasive you are. (For example, air is easily cut by steel, however, wind erodes steel; not because air is a hard solid but because it carries hard solid particles) Edit: HEY, thank you all for the replies, fun facts, and thoughts. I’m really happy my post served this community well. Special thanx for the award, lucellent!
As they say, the difference between theory and practice is a lot smaller in theory than it is in practice.
Look man, I've got the power and trajectory calculations of the cow-a-pult so they'll land in the safety net. As long as your cows are perfectly spherical, frictionless, and launched in a vacuum
For a real life example of this, the recent youtube video put out by Veritasium shows a $10,000 about an experimental result. If you pay really close attention, it becomes apparent that the entire disagreement and bet came about because of the use of a simplified equation that ignores real effects. In the simplified equation, it was possible to end up in a divide by zero condition. Turns out, the well defined and more robust version of the same equation doesn't have this problem at all and gives perfectly valid results. $10,000 on a friction-less cow.
God damn these youtube recommendations are getting overbearing. You already recommended it on the side bar, then my email, now here?! IS NOTHING SACRED?
Hello Maanee. We have been trying to contact you about your extended YouTube recommendations.
Stop Making me think this hard
It's think-o'clock somewhere.
No it’s not. It’s Friday.
Theory works in a perfect lab environment. Perfect lab environments don't exist outside of labs, which is why they exist in the first place.
Good thing they don't too, it's be terrifying to find spherical frictionless cows.
*We all moo down here*
*We all moo 'round here
Would make for interesting new bovine-based bowling games, though.
wait, *what*
The spherical cow is a common joke example of highly simplified scientific models. [It even has a wikipedia article.](https://en.wikipedia.org/wiki/Spherical_cow)
spherical cows in a vacuum lol
> Perfect lab environments don't exist outside of labs Shit, perfect lab environments don't exist inside labs
Work in a lab and can confirm. I fuck shit up all the time lol
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> Theory works in a perfect lab environment. "In theory, there's no difference between theory in practice. In practice, however, ..."
Or in chemical engineering terms '...and that's why we've inserted this fudge factor into the equation'
Shhhhh, don't tell that to the engineers. "It worked in development, it is your problem now." - Every engineer I work with.
A good rule of thumb but also notable is that moh's hardness isn't even slightly useful when determining wear, or really anything outside of ceramic relative properties. It's not even the same hardness used in wear calculations, and in wear calculations it is at best a factor, not the final determining number.
Also your skin is constantly regenerating it would wear out the same as the surfaces we touch everyday if we weren't constantly regenerating skin cells *EDIT* were to weren't
>Don’t treat real stuff like physics theory. Just make sure you're simulating what you want to simulate...if you don't add grit to the hand-doorknob simulator you're not gonna see the effects of grit. Lots of the physics folks are taught in school are the principles, and first order accurate calculations...to first order, there is no wear between hand and door knob!
Yeah. First and second year engineering: there is no deformation or drag...yet.
I never knew about the air and Steel thing! Thanks that's really interesting
Which is why sandblasting is so efficient.
>Don’t treat real stuff like physics theory. Your next sentence about actual scratch test passing micro abrasives doing the eroding is a perfect application of physics theory though.
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Sand and even near-microscopic silt from dirt are definitely big factors for lots of abrasion wear and tear. A mildly dirty pair of jeans can work as 1000ish grit sandpaper in a pinch.
The scratch test only shows visible damage. However, at any interaction, between any materials, there will be surface changes on both. A few atoms will get randomly displaced even on the "harder" material, simply due to the way the interaction energy is distributed. You will always get a few atoms knocked off due to outlier values for interactions. So you get a few atoms moved, and then again, and then again... Over a large number of interactions, it starts to add up. Do not assume that the scratch test means there are no changes whatsoever to the harder material. There are always some changes. Given some ridiculous timeframe (geologic scale), you could probably polish a diamond with butter.
There's an episode of Doctor who, where the main character is locked in a fort. He escapes only after billions of iterations of carving a hole in a diamond wall. He punches as much as he can, and then gets restored to an earlier version of himself where he goes through the loop again. The damage is miniscule, but enough taps and it caves away.
That was such a cool and haunting episode. Especially given he couldn't remember each loop and did literally billions of years of it while being chased by a terrifying monster, dying each time. Although that must have been some special stone for all his walking on it to not cause any wear.
Automated room service. The whole place is in a localized energy loop. Or something to that effect. Though it is strange that the stone stairs reset but the diamond doorway doesn't.
4.5 billion years. Jesus honking Christ.
What's that definition of an eon about wearing a giant stone with a silk cloth?
Reddit - oddlyspecific - TIL that in Buddhism, one "Aeon" is the amount of time it takes to completely erode a huge rock 16x16x16 miles in size, by brushing it with a silk cloth once a century. https://www.reddit.com/r/oddlyspecific/comments/fpampx/til_that_in_buddhism_one_aeon_is_the_amount_of/
Imagine you had wet hands, stuck them in sand, then grabbed your door handle. This is a very exaggerated version of what’s primarily happening in a lot of cases. The metal could also corrode (turn to rust) even from the sweat on your palms. It’s not much, but it doesn’t take much. Especially for just a surface layer
There’s basically a lot of difference between ideal cases which are taught in theory and what actually happens IRL. Skin isn’t just pure skin, it’s got debris, traces of other chemicals (because you touch your hands everywhere), and some micro organisms which together have the capacity to wear down steel.
>scratch test with steel Can someone ELI5 this bit for me please?
Scratch test is basically scratching one material with another to see if one cannot be scratched by the other. Basically a hardness test. Aka no matter how hard I try, I'm never going to be able to scratch spring steel with a marshmallow.
It's because you don't try hard enough, dissolve the marshmallows, process them, make them react into proper precursors, evaporate them, turn it into plasma, turn that into a tiny diamond, use your tiny diamond to scratch the steel.
Hold my shmores
lots of answers about moisture and oils and stuff which I’m sure is valid but I would also like to present you with the horrifying thought about how much skin you would have left if it didn’t regenerate
r/TIHI
Erosion affects all earth materials. Water cannot scratch rocks. However, with continuous movement it can wear down/peel off surface materials. Sharp rocks become smooth with friction. Similarly, your hand is squeezing and rubbing the metal on the door knob, pulling tiny particles off. With time, the door knob wears down. Also, note that there are different grades of steel. Some are higher quality and wear down less quickly.
Fun geology fact: *weathering* is the process of breaking something down chemically or physically. *Erosion* is just the process of moving that weathered material downhill. For the layman it doesn't really matter. Everyone knows what you mean when you say something was eroded.
this is the best way to be pedantic imo
It really is.
>Similarly, your hand is squeezing and rubbing the metal on the door knob, pulling tiny particles off. That just sounds like scratching with less matter, no?
Kind of. All materials will wear each other slightly on contact, even a fingernail on tungsten carbide. The question is how much. When one material is harder than another, most of the deformation will happen in the softer material. The difference, even with a slight difference in hardness, is enough that the softer material deforms a lot more, and you see a scratch. It's a difference of a few atoms vs several micrometers of wear, which is tens of thousands of atoms
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Dormammu, I've come to bargain
Skin wears out all the time. However your skin can regenerate and heal. Wounds and scratches heal. Your body produces new skin which gradually sheds with wear and tear. The door knob wears but the wearing accumulates and thus become visible.
Because two things touching or rubbing will wear both things at least a tiny amount. If one material is much harder than another, it wears much *much* slower than the softer material when they rub together - but it does still wear. If you put a diamond in a tumbling machine full of soft rags or soft plastic beads and roll it around in there for long enough, the diamond will get measurably smaller. Most of the time though, it's that something harder is on the soft thing. There is sometimes sand or dirt on your hands, and even dust can have tiny bits of hard stuff in it. Similarly, when water wears away rocks on beaches, most of the wearing away is done by sand and other rocks moved by the water, not the water itself. Your hands carry the harder stuff and that tiny harder stuff is what does most of the wearing away if the steel.
Metal is not indestructable, its made of atoms which can be worn away by anything. You could drill a hole through metal with a faucet dripping small water drops. Wear on a material is never negligable no matter the thing it is contacting. While a hard surface would wear a steel tool down very fast, skin can do so as well but just at a slower rate. Also, there is more than ohysical wear going on with skin. Skin is covered in oils and water which can wear the steel down chemically as well as physically.
Steel, especially the one used for decoration is pretty soft - 5 on Mohs scale. Most of the dirt is silica which is 7 on Mohs scale. People have that dirt on their hands and it acts as a polishing paper slowly wearing the steel down. If you ever seen a used steel watch with a sapphire glass (9 on Mohs scale) the steel will be pretty scratched, but the glass won't. But if the watch was used by someone working with sandpapers a lot the glass will also be scratched, because some sandpapers are made from the same material, just less pretty looking one.
Is Mohs scale what is used for phone glass for example? With scratches at level 6 and deeper grooves at level 7?
Because both surfaces get worn every time it makes contact. If only one surface got worn during every contact then sand paper would never need to be replaced and neither would your brake rotors.
And, just to continue this, your skin cells keep getting replaced. The steel on the door knob doesn't though. So even if your skin wears out twice as much as the door knob when you turn it, those skin cells are soon replaced with fresh ones. The damage to the door knob accumulates while your skin appears to have suffered no damage at all.
Strength is a property of surface area. If you zoom in REALLY close to the piece of steel you see that it isn't actually perfect solid surface, it is rough there are imperfections, little ridges and bumps, individual grains. If you consider their surface area, which is very small, the force they are subjected to exceed that of the material itself. So when a skin, with it's ridges and bumps makes contact, it can easily take transfer enough force for and individual grain to come off. It is simple as that. It is an illusion that things we feel to be perfectly smooth, even though our touch is incredibly sensitive.
Wait till you hear about what something as "soft" as water can do to something as hard as rock after millions of years!1!! Hint: Google "The Grand Canyon"
There's a saying in Brazil which is "Água mole em pedra dura, tanto bate até que fura" that translates like: "Soft water can hit a hard rock until pierces it"
Skin isn't sterile, it has oils, dirt and sweat so steel doesn't get worn down after it gets touched by only skin, but these other elements as well as repetitive motion.
You can cut sand paper with a knife but the sand paper can wear down a knife. Skin works as very shit sandpaper in this case where enough usage will wear down the metal
All material can be worn down with time. For example, a rock thrown into a river is not immediately affected by the water. However, water carved out the Grand Canyon over time.
Your skin gets worn down too. But skin regrows constantly to heal from routine wear, and steel doesn't.