Confused about "acid test" for silver and other precious metals

how to test if a coin is silver

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Q. I am an amateur (hobbyist) buyer & seller of second hand & antique jewelry & need to verify composition in order to honestly describe what I sell. Recently bought a testing kit on eBay. The silver testing bottle is dark amber in color. As a trial run, I scratched the stone with various silver-colored metals--anything from steel to marked sterling to "mystery" metal. I observe no reaction whatever with any of them. Does the reaction occur instantly? Can I use another type of stone instead of the dark gray one that came with the kit? Or could the liquid in the bottle be defective? Instructions with kit were very sparse. Would appreciate any suggestions.

Jane Bagg

hobbyist - Punta Gorda, Florida

A. I've never used a jewelry test kit, but I am a chemical engineer, so I'll make an educated guess at your problem. My first guess is that the liquid in the bottle is some sort of acid, either nitric acid or a 75% nitric acid/25% hydrochloric acid mix also known as aqua regia. I know you will get a reaction from either silver or gold if they come in contact with either acid, although off the top of my head I don't recall what color you'd get. But there would definitely be a change, or else the metal would completely dissolve. You should see a reaction right away, in under 30 seconds. And yes, it's possible that the acids could go bad over time (say a year or longer) or if the bottle wasn't sealed.

My second guess is that the purpose of the stone is to scrape off enough metal to get a reaction to the acid without doing too much damage to the object you're testing. So the stone just needs to be sharp and resistant to acid. Is it possible that you didn't scrape off enough of a sample on the stone to get a reaction?

If you have an item that you know is silver and don't mind it getting damaged, you could take a drop from the bottle and apply it directly to the silver and see if you get a reaction. No reaction means the liquid is bad, any reaction means you didn't get enough sample on the stone. Or you can write off your e-bay purchase and buy a new test kit with instructions; try typing "silver test kit" into Google. If you have access to a local junior high or high school with a chemistry lab you might be able to sweet talk a teacher into testing your liquid or some of your objects, especially if it could be worked into a classroom lab practical and/or demonstration.

Hope that helped. Good luck with your hobby.

Linda Corrie

- Orland Park, Illinois

A. HI,

I bought a similar test kit off of ebay from a guy who sells many such kits. It included 3 bottles for different purities of gold and one bottle of solution for testing silver. I believe the gold solutions would be the aqua regia and the silver solution is most likely just nitric. Anyway, when I first used the solution it worked very well. Anything made of sterling or purer would immediately turn the solution a blood red color and the silver (if I had put a piece in directly)would turn very dull. The solution also bubbles as it is reaction

with the metal. I often would get bubbles with other metals, but the solution would turn blue (copper indicator I believe)or yellow. I have now had this same bottle for well over a year and it does not appear to be working any longer. In fact, that is why I was on the internet searching "Does silver testing acid go bed?" I am guessing from your experience and mine, and the other persons comments that the solution does, in fact, go bad over time. ( Guess I need to buy a new bottle myself. The first one did work a good long time, though.

Lisa Ferreira

- Sioux Falls, South Dakota

May 4, 2008

A. I have done a bit of testing on various silver colored objects I have. With my NEW bottle of silver test solution (My previous problem was that my solution had gone bad, I would get a reaction just as you describe with any item that was silver plated. I tried this on some old silverware that was marked as silver plate and got the same reaction. My best guess is that what you have is fairly heavily plated with pure silver, hence the initial reaction of the bright red. My guess as to why it stays dark red even after a long time, is that the plating is heavy enough that the solution is used up before it eats through the heavy plating. Your test after the deep cutting shows that the metal underneath is not greater than 75% silver, though my guess would be it is not silver at all. You are getting some reaction as there is still some of the silver plate touched by the test solution. You could try putting more solution on the first area you did to see if you can get thru the plating. It may take a couple of tries depending on the thickness of the plating. I believe your deep cut test already gives you your answer that it is a silver plated item, and reapply solution to the previously tested (but not scratched)area will merely confirm those results.

Herbert Fellows

- new york, new york

March 1, 2010

Q. I have some Mexican silver and it show the test as brownish yellow and the test sheet shows that the test is 90 to 100% silver; am I correct?

ray robey

hobby - temecula California

May 28, 2010

A. The test colors for silver that you have posted appear to show silver content at 80% silver but the yellow reaction indicates a base of tin which would be common in Mexican silver.

Kerry McGee

- Prescott Arizona USA

Q. I am totally new to silver and color blind LOL. I am only interested in purchasing .999 rounds and bars for investment sake. What are my best choices for testing in this situation? Is acid the only way to determine quality? Would appreciate any help!

Ron Cox

March 31, 2011

A. If at odds for testing silver, with acid try using any gold acid to the silver; it'll turn milk white and stay milk white. If silver is plated the gold acid (10 kt--up) will eat through the silver plate and start eating the base metal, by bubbling and acid will turn green. it's a foolproof method, and you clean the acid spot with jewelry rouge.

Source: www.finishing.com

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