Q. I need to determine if all the chrome has been stripped from a large part that we are going to salt bath nitrate, I remember a chemical we used to instantly detect if spots were missed. I think it was copper sulfate liquid. Is that correct? If so where do I find it? If not what can I use.
A. Purchase dry crushed copper sulfate crystal from a chemical supplier, mix about 1/4 oz. by wt. crystal (large tablespoon size) in a beaker of 200 ml of water. Mixes best on a warming plate with a stir bar. Slowly add 5-10 drops (10 mils) of sulfuric acid until the crystal is totally dissolved and the solution is a pale blue. Keep it in a sealed bottle out of direct sunlight. Label according to regulations.
Swab it on with a q-tip in the area you want to verify chrome removal. Bare metal will turn copper color, chrome or other coatings will not. Wipe off any access with a tissue. This technique works on most ferrous alloys. It won't work on CRES..