I recently acquired a small antique bronze statue and notice that it is very heavy for its size and has a rich golden color (as opposed to the brassy color other bronzes in my collection have). I have heard that occasionally bronze alloys could have some gold in them and am curious if mine might also. I intend to keep the statue as is, but would just be curious to know if it indeed has any gold. Does anyone know of a way I could determine whether it contains gold, but without destroying the statue?
One thing I thought of doing is calculating the density of the statue and comparing it to the known densities of common bronze component metals: i.e. copper, tin, zinc, and silver. If the measured density is higher than any of these, that would mean that the alloy contains a portion of denser metal, right? I think this might work well except for the possiblity that it contains lead, which would make it extra heavy as well.
Is there any other simple way of testing anyone can think of? Extra points if someone can suggest a way of estimating the actual percentage of gold…
Hmmmm… If it was the presence of some other metal like copper, it would be easier, beause you could swab a small area underneath the base with mild acid to produce salts, but gold is more or less chemically inert.
I think there are too many variables to be able to ascertain the constitutents of the alloy without assaying it, and that’s assuming it’s made of the same stuff all the way through and not, say, a hollow bronze casting cunningly filled with lead. Assaying by mass spectrometry should require only a tiny little scrape of a sample though.
The other thing to consider when calculating the density is that for x volume of metal P and y volume of metal Q, you don’t necessarily get x+y volume of alloy, because of the way the different atoms pack together (or something like that, anyway), so that’s another set of variables for the density estimation process.
So would the failure to produce salts mean that gold is present? And if it was an allow of, say, gold and copper, wouldn’t it still produce copper salts even if the gold didn’t react, or would the gold render everything inert?
Nice one; other practical suggestions include:
calculate the total amount of gold originally existing in the world, then measure the total amount of gold in the world to see if any is missing.
BTW (and off-topic) the acid thing reminded me of an ancient technique for making artifacts that appear to be solid gold; you make them out of an alloy of gold and copper, then etch them in acid, dissolving most of the copper from the surface; this leaves the artifact with a porous and rough surface, but gold is quite malleable, so you just anneal and burnish it and it looks like a solid gold item.
No, if there’s copper in there, you’ll produce copper salts in most cases, unless the particular combination of metals in there happens to form a resistant alloy (like stainless steel, but I’m not sure if similar alloys are known for other metals).
What I meant is that there’s no simple chemical test for gold in the same way as there is for, say, copper or silver.
I pawned a ring years ago. The jewler rubbed it onto something and performed some sort of test to determine the gold content. You may be able to do something like that.
You can look up the density of bronze in a chart, I saw one online that claimed 8.1g/cc. Obviously, that’s an average, not a fixed value, but it should get you in the ballpark, and a lot more easily than trying to deal with the component metals.
In general- no. Gold plating yes, gold alloy- no. It could have some more tin that usual, or even some other metals, but the chance they just threw some gold in there is minute.
I should explain a bit more – it is an 18th C statue of the Hindu goddess Durga used as a household devotional statue (murti). I am confident of the age and that pieces of this size at this time were always solid cast using the lost wax process. It is known that sometimes wealthy families would have the alloy include gold. Gold in this case would make the statue for more valuable literally and also heavier, both of which would increase its devotional value. It was not common, but did happen. This is the first piece in my collection that might have any gold in it.
Like I said- very doubtful. With Gold alloys either there is enough Gold in the alloy to make it obvious, or there is no gold at all. Yes, I have heard of 10k gold alloys, but nothing less than that. Any decent goldsmith or pawnshop has tests that will show if there is gold in it- the take a scratch onto a plate and do an acid test, as Kalhoun had happen. If the statue is 18th century they woudl have added gold leaf or plating if they had wanted a small amount of gold. Making the alloy 10% gold (or so) does nothing.
