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

Trying to draw a firm line between "solid" and "liquid" for mixtures is silly, anyhow. If you can't point to a phase transition with an associated energy change (heat of fusion), there's not a firm boundary.

In science class, there's "solid, liquid, gas", then eventually "plasma" gets added 00 but even for pure substances, you go on to crystal phases and allotropes and endless other complications. With mixtures, you get gels, colloids, emulsions...

In the real world, between "solid" and "liquid", there's "gunk".

 

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I spoke with my friend who is a chemist in the lubricants division for Chevron, and he says liquid, so I'll accept that I'm wrong... until I can convince him that it's a solid.

 

Problem is, "common sense" really only gets you so far when it comes to rheology. Newton covered the "common-sense" parts, but there's a reason why so many fluids are called "non-Newtonian".

Since I haven't even taken the classes, never mind worked in the field, I can't help much with those non-common-sense aspects. But taking Doug's point about particles, let me ask this: isn't there a good chance that a trickle of thin, not very viscous liquid, running across machinery where some parts are covered with grease, but others covered with dust, might actually pick up more particles (per unit volume) than the grease has?

The answer, of course, is "who knows?" I don't know where the water would come from, what it would run across to get to the planchet, and how much debris it would pick up along the way. But I have just as much right to speculate as the next guy.

 

Posted something.... decided it wasn't worth my time. Nevermind.

 

We need think about aqueous solutions and suspensions too. Things like coffee, cola, milk, honey, jelly, etc. ... yes, even beer. Good chance these have gotten on planchets or dies. Perhaps these things are confined to the lunchroom today, but in the past, mint workers probably could take their drinks and snacks into the machinery rooms. Not too big a stretch to imagine a bottle of cola or cup of coffee falling into a bin of planchets ... sometimes maybe with a little deliberate help. Having solutes or particles in the water can make a big difference. Evaporation rates can be dramatically lower, the liquid may form a higher-domed bead, viscosity will be increased, particles or crystals may start to precipitate, solutes may react with metal, adhesion of the bead to metal may be greater, etc. Put a drop of pure water and sugared cola on a quarter, and see which lasts longer and which leaves a residue.

Cal

 

I was striking some coins today and performed a test.
With the planchet sitting in the coining chamber, I put a small drop of water on the planchet. The drop was located were there was a recess in the die above it. The recess was a facial portrait. I expected that this recess would trap the water when struck. The result was that the entire coin was fully struck except where the water was trapped. The facial portrait details were missing and there was a smooth shallow depression on the struck coin where the face was supposed to be. This was as I had expected. Water is incompressible, and if it has nowhere to escape, it will make in impression in the planchet. If the drop was near the edge and not in the center, it might squirt out at high velocity before interrupting the striking.

 

Our hero of experimental verification!

Any chance the experimental subject will be offered for sale?

 

Thanks for doing the test. Have you tried oil or grease, and can you post pics? Cal

 

Thanks for confirming, that is exactly what I expected to happen.

Question: did this have the typical appearance that we associate with coins "struck through grease"? That is, if we were looking at a coin from the mint, would there be any significant difference between a "greaser" and a "water" coin? My suspicion is no, probably not.

 

The area where details were obstructed by water had the same surface texture and general appearance of the original planchet. Grease tends to stick to the die face and spread out more after repeated strikes. It also typically has metal particles bound in it. Water would dissipate rather quickly after repeated strikes. The water strike-through area is a little more shiny than the typical grease strike-through.

 

I think what I'm trying to ask (and was implying without saying): planchets at the mint tend to be somewhat rough (from tumbling, handling, etc), with a large amount of contact marks. If you get a blank planchet, or a planchet struck sufficiently off center, you'll see that. When we see a "struck through grease" coin, it tends to have a rough appearance with a lot of tickmarks. Would a "struck through water" coin have the same rough appearance?

My suspicion is that yes, it would. From what you say, that the water struck coins had the same texture as the original planchet, leads me to believe that generally, "struck through anything" will have roughly the same appearance and will thus be virtually indistinguishable to the collector.