But for a Smut

Q. We do hard chrome plating (conventional). What is the best chemical pre-treatment for hard chrome plating? We currently use an aluminum oxide blast and a reverse sulfuric etch. We are concerned about the smut created by the reverse sulfuric etch. We manually scrub the smut off with Scotch-Brite. Is there a chemical desmut that may work? We run mostly carbon steels and some stainless steels. —H.R.

A. Over the years I have seen many different approaches to removing smut from carbon steel parts prior to plating. Sadly, I am not aware of any “silver bullets” for desmutting of parts. Some people suggest a cyanide-based formulation while others talk about using acid/surfactant formulations to do the job. I suggest that, as a start, you should consider using a chromic acid reverse etch for your carbon steel parts. One formulation for chromic acid reverse etch bath is 26 to 30 ounces per gallon and an operating temperature close to that of the plating bath temperature. Typically, an etch of 15 to 30 seconds at one amp should be adequate.
If you want to investigate various other types of formulations for desmutting, try a Google search using the terms “desmutting carbon steel” or “desmutting stainless steel.”