Would coin struck through water look like one struck through oil/grease?

Everyone understands how grease behaves when you smear it around on a surface, and how water behaves when you do the same thing.

I don't think everyone understands how each behaves when pushed against a metal planchet with many tons per square inch of pressure. (I certainly don't.)

What I do know is that both are effectively incompressible at pressures like that, so I'd expect them to behave similarly. They have different viscosities, but I don't think that would make much difference at those pressures and striking speeds.

I don't think I agree that grease is "a solid, not a liquid", but I don't have the material-science background to back it up.

I do have enough chemistry background to know that water's boiling point under tons per square inch of pressure isn't 100C. I'm sure the striking pressure is well above water's critical pressure (around a ton and a half per square inch), so any water on the planchet can't "boil" at all during striking. Supercritical fluids are really interesting, but again, I'm in no position to teach about them.

 

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I see what you did there. And I'm stealing it.

 

If the water has an escape path that allows it to completely run off the die before the coin is struck, then it won't leave a trace. If it doesn't, it will.

Dan Carr could easily demonstrate the effects of a drop of water in the devices or a mist covering the die, should he so choose.

 

Take a look at the 1881 VAM 17 Morgan dollar. The portrait is covered with small, raised rings. These could be due to water droplets being present between hub and die when the die was being made. If this is the case, then water droplets present between die and coin could leave incuse rings on the coin.

 

Thank you very much. Nice to know Leroy himself has something to offer on the topic. Hurrah for VAMmers!

Cal

 

It's a solid unless under sheer stress. In the later case, it acts like a fluid.

 

This is about what I'm thinking too.

But I'd compare it more to a tire that is hydroplaning. This occurs when a thin layer of water exists between the tire and the road; essentially the tire rides up onto the water and loses traction.

I'm picturing the water spreading out fairly well and affecting the luster more than the strike. Of course if there's a lot of water than I'm with Conder101 and think it would look a lot like grease.

It would evaporate almost immediately and affect only a couple coins.

What a question!

 

But from what GDJSMP said, actual tests have shown little heat generated during the process so the main way the water would be removed between strikes would not be evaporation. One would expect some water to be attached to the coin that was struck and some remaining in the die. So the first coin struck would be impacted most.

 

It really depends on which die the water was on, where it was on the die, and the humidity in the air. In Denver or CC, water remaining on a hammer die would be fanned off by the motion of the die while striking. In Philadelphia or New Orleans, not so much. Water sitting in the devices on the anvil die would stick around for a while, and probably be carried away on struck coins rather than evaporating.

 

An interesting experiment for Dan Carr would be to do a strike in a mist of water.

 

The coin doesn't get hot but, I believe, the surface does from pressure and friction. The water would be hot enough to vaporize when the dies separated if it were very thin against this surface.

 

Really, people. Let's use some basic high school science here. We're talking (around) 120 tonnes of pressure.

At that pressure, the temperature would need to be 13500 F to reach saturation.

Yeah, water is going to stay a liquid at these pressures, and it is going to be incompressible. Water is going to behave just like grease (which doesn't act like a solid.... edited?). Water, beer, gatorade... they're all going to be the same.

Now, once the pressure is released, the surface of the coin will be hot and the water will quickly evaporate. But, at the pressures in the striking chamber, the water will not boil.

 

Sorry but being in the water and restoration business, if H20 has an outlet, you can call it gone. The planchets have got to be 70 + degrees before strike, and a mist of water, will not remain after strike.
Maybe a droplet contained in plantchet striations could be trapped in the recess of the die. But a film of water would dissipate.
I do agree with the loss of lustre theory.

 

Grease, like ice cream, is a fluid solid.

 

Grease has at least one more molecule, that, adds Viscosity to the bearing of the liquid.
The equation has more to do with the properties of the so called liquid being struck. And, oil has a bonding agent.

 

What is a fluid solid???

 

Non-Newtonian fluid.

 

Never heard of it called a Fluid Solid. Would that be dilatant? Then I guess a Solid Fluid would be thixotropic.

Still not buying into grease (the type used to lubricate equipment such as a coin press) being a solid. The stuff in a grease gun is going to deform under it's own weight in reasonable period of time. But then, you know the old rheologist expression, "you say thixotropic, I say pseudoplastic" so in the end, it really doesn't matter