What is the easiest and safest way to test metal analysis on gold coinage? I am needing to determine the carats of a gold Hyperpyron, the only way to differentiate the coin from imitations is 20 1/2 carats or 18 carats. I know the local jewelers would have some sort of test but would it damage the coin? What other options are their available?
Water displacement/volume(milliliters) and grams will give you density. 19.32 grams per cubic centimeter for pure gold-24 carat https://www.convert-me.com/en/convert/density/ EUREKA!
I use this method for determining specific gravity (density). It’s very simple. Use distilled water if you can. http://www.johnbetts-fineminerals.com/jhbnyc/articles/specific_gravity.htm
Here is the method, you may lower the coin carefully in a graduated cylinder with a plastic forceps/tweezers. It will tell you the relative density(D=M/V) if it is not pure gold. If it comes out as pure gold than you may need the further jewelry test because that density could be faked but I would think that is kind of rare. https://sciencing.com/tell-pure-using-water-displacement-8109592.html
Indeed it would be. I use a paper clip bent into a small loop with a handle and I lay the coin on the loop. Then I lower it into the water until covered. It works surprisingly well.
I think Kentucky has the best idea. That said, I bought a Brutium Punic 3/8th Shekel and wanted to confirm it was electrum. The coin looked too silver to me. I did a SpGr test. I think the test confirmed gold in the mix. It is hard to say without XRF analysis what is in the coin. You can see my results here: http://rrdenarius.blogspot.com/2018/06/spgr-to-estimate-gold-content-of.html and in cointalk here: https://www.cointalk.com/threads/spgr-to-estimate-the-gold-content-of-an-electrum-coin.317989/ Light source changes the yellow tint of my electrum coin.
I'll pick a couple of nits here...first the method does not tell you the density, and I'm not sure what the "relative density" is. It tells you the specific gravity, the ratio of the density of the object to a standard, usually water. Since water is usually close to 1.0, the specific gravity is very close to the density. Secondly, the weight of a submerged object is the weight of the water it displaces. If your tweezers, paper clips, etc. don't displace any water, you are accurate, otherwise, not so much. Maybe "close enough for government work".
I always tare the scale with the paper clip submerged to the point where the coin will be. I then lift the paper clip, place the coin on it, and lower it to that point. An analytical balance would be more accurate, but as long as the coin is clean and no bubbles form, the results are reliably diagnostic for most purposes. It’s fun and easy to do. I use the same technique to check for meteorites.
Yes, this method(the one I linked to) does tell you the density. This is not the same as the specific gravity test. You use the tweezers to lower the coin into the graduated cylinder and let it the coin only rest on the bottom pulling the forceps out completely to measure the water displacement only of the COIN = VOLUME. DENSITY = MASS/VOLUME. The method I have shown and given links to is density, NOT the SPECIFIC GRAVITY test. Yes their results are close. What I meant by calling it "relative" is that it can be undermined with a careful alloy to mimic the density of gold but this is rare. over the top with nitpicking folks. I guess it goes with the territory?
I use a Kee Gold Tester... they are pricey, but, like said earlier... go to a Jewelry or Coin Shop, and they probably have a gold tester. The only issue is that Accuracy would be a little hard to determine within only a couple of carats... at least on the Kee Tester, as it doesn't have a digital display or anything... a better tester may, though.
If you do not know the alloy material and percentage the rest of the coin is made from, you have a mess. For example ( quote) : Different alloying elements have different SG's, e.g., 8.90 for cobalt and nickel, 8.94 g/cc for copper, 10.49 for silver, 12.0 for palladium, 12.4 for rhodium, 21.45 for platinum, etc. It is possible for alloys of different gold concentrations to have same SG, and for alloys of same SG to have different gold content. An alloy of 83 vol.% platinum and 17 vol. % copper will have roughly the same SG as 100% gold. Even knowing the composition (wt.% or at.%) of a multi-component alloy, it is difficult to accurately calculate the exact SG because non-ideal thermodynamic interaction of atoms will affect the volume. Porosity is another problem." you can find data for simple alloys such as gold-silver and gold-copper. But because of multicomponent effects noted above, 9 carat gold has SG range 10.9-12.7, 18 carat yellow gold 15.2-15.9, 18 carat white gold 14.7-16.9, 22 carat 17.7-17.8, sterling silver 10.2-10.3. https://www.finishing.com/189/07.shtml You need to have a component analysis before the s.g. is calculated and compared. Maybe someplace there is an analysis of mining sites where the gold for the coin came from, but often that is not possible. If you can find the process that the author in post 1 used to determine the part on carats of hyperpyrons used to do sp.gr. and repeat it , would be a fair guess. IMO , Jim
You can't possibly have meant to write this. Here's a table of various metals' different weight per cubic meter, all of which will sink in (and thus displace the same amount of) water:
Actually I do mean that a suspended submerged object will be the weight of the water it displaces. BTW, in the United States density is usually given in g/cubic centimeter or g/mL. Even with that, the density of aluminum is 2700 kg/cubic meter or 2.700 g/mL
