Acid testing is used to confirm the stamped purity of the gold we sorted in step 1 and to determine the purity of un-stamped items. We use pre-mixed strengths of nitric acid, one for each karat of gold. We start by taking a small sample of gold by rubbing the item onto a hard testing stone. This sample does not harm the appearance of the piece and the amount of gold it removes is microscopic.
Next we place a drop of 10K acid on the sample, if the sample disappears then the item is not gold. If it does not disappear then we use 14K acid on the sample, if it disappears then the item greater than 10K but less than 14K. It it does not disappear we move on to the next karat of test acid and so on until we determine the correct purity. For silver, acid is also used but normally applied directly to the piece itself. The acid will turn different colours. For example a creamy colour for silver 90 to 100% . A gray colour indicates 77-90% silver and a light green colour means the item is 65 to 75% silver.
The use of testing acids can be dangerous and proper safety equipment should be worn and manufacturers safety data observed. We encourage you to watch the testing process, but please do not touch the acids or get to close to the test stone.