Jewellery making often requires repeated heating of workpieces - Soldering, annealing, enamelling. This will result in the metal oxidising - becoming covered in black scale.
Step 1: Make the Pickling Solution
This consists of a solution of about 150 ml of vinegar with a tablespoon of salt dissolved in it. The best kind is cheap clear stuff. Cheaper the better.
Step 2: Heat Up the Mixture and Stir.
Heat up the mixture in a microwave, stir until dissolved.
Be careful - vinegar is a weak acid. An aqueous solution of Ethanoic Acid formerly known as Acetic Acid. If you get it into your eyes wash them out immediately.
Other than that the solution is quite safe - after all you do put it on your fish 'n' chips!
Step 3: How to Use.
Put the objects to pickle in the solution.
I use a clip lock container. Put the lid on and shake. Leave until the scale is removed. Usually half an hour will do the trick.