I HAD SOME MATERIALS WHICH IS COATED OVER WITH SOME METAL SULFIDES, WHICH BECOME A BLACK COATING-LAYER AS COATING AND IT COULD NOT BE REMOVED. 1. I WAS ADVISED TO USE SODIUM THIOSULFIDE -NO RESULT
2. THEN, BY SIVER NITRATE SOLUTION, SO THAT THE SULFIDE WILL BECOME SILVER SULFIDE AND METAL WITH NITRATE TO GET CLEANED- BUT NO RESULT....!
3. I WAS TOLD TO USED CORBONIC ACID TREATMENT BEFORE USING THIS SILVER NITRATE SOLUTION - NO RESULT...
4.THEN, FIRST WITH SODIUM BICORBONATE, THEN WITH AMMONIA LIQUID BEFORE TREATING WITH SILVER NITRATE - NO RESULT.......
CAN ANYONE SUGGEST ME HOW TO BALANCE THESE MATALIC ION OF SULFIDE TO BE REMOVED WITH HELP OF OTHER IONIC EXCHANGE PROCESS. AND FURTHER ANY OTHER METAL NITRATE OR COMPOUND WILL BE HELPFUL TO ME IN REMOVING THIS BLACK STRAINS...