Anyone here EVER get a specific gravity over 10.0 for a shipwreck silver coin?

Insider2

In the past decade, I have taken the specific gravity of at least sixty 1883 8 Reales from the El Cazador in all conditions from decent to a corroded lump of metal. Not one coin has had a specific gravity over 9.8. They range from 8.9 to 9.8. These coins are all over the place both raw and certified. Can anyone explain a reason for their LOW specific gravity? Does saltwater "leach" the alloy?

Sapyx

It isn't going to "leach out" the high density silver and leave lower density metals behind. The opposite, if anything.

I can think of several things, chemically, that might affect the specific gravity of a piece of silver submerged in salt water for a prolonged period.

Silver exposed to chloride can form horn silver over time. Horn silver (silver chloride) has a lower density than metallic silver and is notoriously difficult to remove. A thick layer can alter the specific gravity reading.

A shipwreck coin is likely to have marine encrustations, either biological or chemical in origin. These encrustations are going to be lower density than silver.

If horn silver or encrustations are removed by harsh cleaning, then the coin is likely to be covered in pits and holes. The specific gravity testing solution might not penetrate into those pits and holes, leaving bubbles which the specific gravity measurement will think are part of the coin. And air, of course, is much less dense than silver.

MrEureka

@Sapyx said:
It isn't going to "leach out" the high density silver and leave lower density metals behind. The opposite, if anything.

I can think of several things, chemically, that might affect the specific gravity of a piece of silver submerged in salt water for a prolonged period.

Silver exposed to chloride can form horn silver over time. Horn silver (silver chloride) has a lower density than metallic silver and is notoriously difficult to remove. A thick layer can alter the specific gravity reading.

A shipwreck coin is likely to have marine encrustations, either biological or chemical in origin. These encrustations are going to be lower density than silver.

If horn silver or encrustations are removed by harsh cleaning, then the coin is likely to be covered in pits and holes. The specific gravity testing solution might not penetrate into those pits and holes, leaving bubbles which the specific gravity measurement will think are part of the coin. And air, of course, is much less dense than silver.

If the "lower density metals" are leached out, would that leave cavities within the coin, or would silver chloride (or something else) fill in the gaps? Either way, I can see how it would lead to a lower specific gravity reading. Also makes me wonder if the coins ring any differently than non-shipwreck coins.

Also, for those unfamiliar with the El Cazador wreck and who may be wondering why they haven't seen salvaged Cap & Rays 8 Reales, the coins are dated 1783, not 1883.

Insider2

Thanks, I've considered these things. Most of the coins have been stripped "raw" from harsh cleaning. We've all seen them. Microscopically there are no holes but we must assume that is the case and the simplest answer. I have just made the decision to cut one of my pieces in half and have it analyzed. What a dummy, I should have done that years ago.

YQQ

would a XRF machine not be able to tell you? saving yours from being cut?

jgenn

@Insider2 said:
I have just made the decision to cut one of my pieces in half and have it analyzed.

Excellent! Please keep us posted on the results.

Timbuk3

Interesting, yes, please keep us posted !!!

Insider2

I'm taking one over to the ATS to have Rick test the composition. No sense cutting one in half as now I'm sure the metal will be the same throughout the coin. The "normal" 8 Reales have all been over 10.something. Unfortunately, my present equipment is primitive. At ANACS our SpGr balance went to .000 giving an accuracy to the hundredths. At INSAB our balance went to .0000 giving us an accuracy to the thousandth. I'm using one possibly only good to a tenth now. Still, these salvage coins are too low for some reason.

jgenn

XRF of the surface should show high silver results due to the surface leaching effect. It sure would be nice to get a sample from the interior of the coin if you can still be talked into having one cut in half.

Insider2

I agree but I'm going to scrape down a millimeter into the surface. Problem is I can't lay my hands on my coins at the moment and still looking.