Silver testing kits used to have a sulfer compund in them. It was mixed with a bit of water to make a paste,,only a very small amount was needed to test a single article. The paste was spread onto the item in question in a small area and then heated very slightly, just warm to the touch. The sulfer combines with silver and forms silver sulfide which is black. No black stain,,no silver. You can use some common brands of mustard (Frenchs brand IIRC) that contain a high amount of sulpur and they will work the same trick. The black stain can be removed with little polishing with any common 'silver cream' polish or just some white vinegar on a cloth.
This will not tell you if the item is solid silver,,it may only be silver plated. Check other areas of the item to see if plating has worn off or base metal of another color can be seen. Try a magnet to see if base metal is iron or steel.
Any of the so called 'German Silver' or 'Nickle Silver' alloys will not respond with a black stain mark with this test. None of those alloys have any silver content.
>
The sulfer in rubber from the vulcanizing is the reason a rubber band left stretched around a silver object would leave a black mark over time.
