American coin silver - what is it really?

[Jag]

Two basic questions about American coin silver. I'm starting to try to measure specific gravity and finding some surprising results. Some of this is undoubtedly due to poor technique, but it led me to wonder whether there is some variation in the specific gravity due to variations in the metal itself.

My first question then, is whether copper was the only alloy mixed with the silver, or were other metals (such as tin) were sometimes used?

Secondly, the oft-quoted percentage of silver in coin silver is 90% - and presumably silver from the mid-19th century on that is marked "Coin" will meet this standard. I also gather there can sometimes be more than this amount - for example if Pound sterling was melted for use. But was American coin silver sometimes made with less than this amount of silver in the mid-19th century and before? Especially since there was no legal requirement on American silversmiths to meet any particular standard? If so, has anyone published any scientific observations of the range of alloys found?

[dragonflywink]

American coin does vary, there have been some studies done, with fineness ranging from below .750 to over .950 - there wasn't really a legal requirement that silver marked as 'Coin' be of at least .900 fineness until the National Stamping Act of 1906. Coins from different countries weren't the only source of silver (even the commonly used Spanish dollars varied, depending on when minted), damaged or out-dated silver items, often in the different standards of the 'old countries', were also melted down; bullion and sheet silver were also available. Not too long ago, had a set of twelve unmarked early to mid 19th century coin spoons checked with an XRF spectrometer, they were .837 silver with mostly copper, and like most of the pieces I've had tested, traces of some other metals, zinc, tin, nickel, and iron are some that I recall from the results on various pieces.

~Cheryl

[Jag]

Thank you very much for your detailed answer. That wide a variation in percentage would cause the specific gravity to vary by a lot from the quoted figure of 10.3 g/cm3, which is reassuring since it means my weighing technique may not be as bad as I thought. I found some of the marked pieces I have to be less than this (though well above the measurements I made of silver-plated objects).

Specific gravity testing has been kind of fun since it allows me to go through some of the "questionable" pieces I have and determine that most of them were indeed silver-plated. It's nice to have a non-destructive test - the main limitation is being unable to test pieces with wood or hollow handles.

A spectrometer test would be even better - can I ask how much it cost to have a spectrometer test done, and where you found a place to do it?

[dragonflywink]

My friendly scrap buyer has a top of the line spectrometer, try not to abuse his generosity in testing whatever I bring with me when I visit his office...

~Cheryl