Will Specific Gravity Test harm a coin

Yikes! I had no idea how many fakes were available on Ali. Most of them look cast, which makes it a bit easier to tell, but some of the fakes are actually die struck. I'm just a beginner collector, and a lot of those fakes looked good at first glance.

As for weighing and measuring them, the 1955 DDO weighs in a little bit heavy (3.15g instead of 3.11g) but definitely not out of the range or possibility, and the diameter and thickness are spot on.

Now I'm even more interested in the Specific Gravity Test.

 

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I'd say the specific gravity test is probably useless for that coin, because there's no reason to think it would be made from the wrong metal.

It makes sense for counterfeiters to use base metals (almost always less dense) for fake silver or gold coins. It would make no sense for them to use anything other than the right alloy for a fake copper cent. It's easy enough to get a bunch of old cents and melt them; it's just as easy to make the alloy from its components.

It's possible that the coin would have the wrong specific gravity, but it's extremely unlikely, IMHO.

The specific-gravity test is also hard to do well -- tiny errors in weight turn into large errors in specific gravity. You'd find it very challenging to measure it within 1%, which is about the weight difference you found.

 

If you look around, you can find perfluoromethyldecalin for $30 per liquid ounce in small quantities. Not much is needed to do specific gravity, and it's reusable for this.

It's an interesting compound. It binds oxygen, so an emulsion of it was developed as a blood replacement and approved by FDA. The main problems were adverse reactions in some patients, need to breath pure oxygen, and it had to be kept frozen for long-term storage. So it went out of production.

You can make fairly dense solutions of highly soluble sugars and salts. These can be bought commercially too from medical lab suppliers. They're used for fecal flotation of parasite eggs!

Cal

 

Guess I'd need to look harder, then.

Why would it need to be kept frozen, I wonder? How would a perfluorocarbon spoil?

I'm looking at tetrabromoethane, density a hair under 3, which is probably cheaper. Could possibly even make it myself with pool chemicals and calcium carbide. I'm not too happy about the toxicity profile, though, and I'm not 100% sure I'd trust a brominated compound on metals. (I know one of the formerly popular coin chems was brominated, so maybe I shouldn't worry.)

There's also sodium polytungstate solution, density up to 3.10, which sounds really interesting -- but it looks like it's even more expensive.

I wonder if the whole "dunk it" approach will die in the face of cheaper and better 3D scanning. If my iPhone 13 can take a short video of each side of a coin, then generate a dimensionally accurate 3D model of it, it would be dead easy to get a volume from that. Hmm!

 

The perfluorocarbon is chemically and biologically stable. The problem was the emulsion separating. In addition, the blood substitute had organic ingredients like albumin and vitamins in it.

Keep us posted on what you find for high density fluids for specific gravity determination.

Cal

 

Oooh -- icky life stuff. Got it.

Chances are poor that I'll pursue it more than I've already posted, but if I do, I'll try to remember to brag about post it here.

 

You just have to punch a hole in the coin to tie the line...

 

I remember reading somewhere about ammonia gas being collected by the downward displacement of mercury!!!

 

In your garage???

 

I've done worse. Sometimes even on purpose. But it's academic right now, as I don't have the carbide or the bromine source.