Best Precious Metal Testing Stones: Upgrade Your Testing Kit

Question
I currently have an economy stone that came with my testing kit. I definitely want to upgrade but don't know what to upgrade to. I test a lot of silver and find that it is very difficult to get a decent scratch on pure silver and nearly impossible to get deep enough in some thicker items. I also notice that the more i use the stone the worse this gets.  I am looking for a stone that will work well on the harder metals and thicker pieces so that i can actually get a decent scratch and also not wear down too quickly. I also have read that some stones work better with the acids than others but not sure if this is true. Please help me find the right stone so i don't end up having to try them all!

Answer
Ali, thank you for this question.

Generally the stones provided with acid gold testing kits work well enough. Sure, some stones are softer than others and I personally do not like the soft ones nearly as well as harder test stones.  I am not aware of where to purchase the stone only and not the entire kit.

I suggest you buy a geologists scratch plate, a piece of unglazed ceramic tile used in the field to see the scratch color of mineral specimens.  These are available in black and black does make it easier to "read" the reactions to acid. The ceramic is certainly hard enough.  An inexpensive knife sharpening stone will work if of the medium grade and a solid stone, not a composite which might absorb the acid. (Any knife sharpening stone should be dry and not come oiled.)

If you can find a scrap piece of unglazed ceramic tile with a solid surface, rub some metal on that to see how it works.  All you really need is a flat surface to  hard enough and gritty enough to take a streak from metal rubbed against the stone. A solid stone or ceramic is needed to withstand the acid.

I suggest you get a sharp awl, small fine file or perhaps a basic jewelers engraving tool with a fine point. Often the test must go through a surface which is too much for a stone without badly damaging the item.  An old watch case suspected of being gold is an example. Rolled gold plate is often thick and the best test is inside the case in a hidden place with a scratch through the surface with the file or graver and acid applied gently to the scratch to look for tell tale greenish residue from base metal.

Ali, I do hope this helps and God Bless and Peace.   Thomas.