Can't get rid of sealing smut

Eugenie

I would suggest you check or adjust the pH of your sealing bath (nickel acetate). We have found that the mfgr's specification for the pH does not always produce a smut-free finish. But don't cut back on your seal time- that is critical with regard to coating thickness.

Follow-up with seal quality testing.

I must ask a few questions to see if I can figure out what you are asking.

1. Are the parts dyed or clear.. I'm thinking dyed.
2. What alloy are you plating? 2XXX series in my experience smuts after dying if there is a deficiency of aluminium in the plating tank.
3. Are you deoxidizing the parts correctly after etching?
after etching the aluminium the parts will come out a grey to black depending on the alloy and duration spent in the etch tank, they will then need to be deoxided/desmutted. the parts should come out a white/silver out of the deox/desmut and then be rinsed thoroughly before insertion into the plating bath.


I hope this helps.

Is this a nickel acetate seal? Smut may be due to a high pH. Adjust the pH to about 5.8 using acetic acid [on eBay or Amazon] or ammonium hydroxide as necessary. Ask your additive supplier for technical support.

For further assistance, there is a chapter on sealing in Mr. Probert's book: ALUMINUM HOW-TO -- The Chromating - Anodizing - Hardcoating Handbook.

Without knowing the additive, and tank parameters, it's hard to answer your question. There are numerous causes for sealing smut.
I would contact the supplier of your additive for advice, especially if the additive is designed to reduce/eliminate smut.