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Problem with black chrome plating

Q. I manage the buffing room at a gun refinishing shop and I am getting frustrated redoing my work. We started black chroming guns for a well known manufacturer. After doing about 250 guns (before this we were only doing about 2 black chrome guns a week for individuals) we started having a problem getting the chrome to throw into recess areas such as the trigger guards and serrations. We thought that the heat was the problem so we brought the tank temperatures down to the high 70's. When this didn't work we sent off a sample for analysis. We are using a 75 gallon tank for this process, and we were told to add 1.5 gallons of reducer. Upon adding the reducer the solution started to foam and almost bubbled over. After this it got worse and would barely plate at all. We got in touch with our lab/supplier and they told us to add .25 pound of sugar and a .25 pound of barium. This time it would plate but it was not black it was green, and the lab offered no explanation for this. The plater switched over to our big rectifier (the one we use for hard chrome) after turning it up to 300 the gun turned black after 40 minutes of plating, when the tank is right it only takes 10-15 minutes with the small rectifier. If this helps we hard chrome our stainless steel prior to black chrome and nickel plate our carbon steel prior to black chrome.

Thank you in advance for any and all help.

Harold B [last name deleted for privacy by Editor]
gun refinishing - Brooksville, Florida, USA
2003

A. Sorry that you received no help here yet, Harold. I don't know enough about the subject to contribute myself. But if on-site tech service from the supplier is unavailable, there are other suppliers these days, or you could even consider retaining help from a black chromium plating shop outside of your area. Sorry again, and good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey