Topic: Cyanide copper tarnishing
Some of our antique copper part are tarnishing after lacquer. sometimes
it take a day or two and doesn't happen all the time. What can i do to
prevent this from happening?
Re: Cyanide copper tarnishing
Are you sure your parts are fullied dried before the laquer is applied? Are you sure your electostatic gun is working properly? Has your laquer been contaminated? My guess is it is one of the above.
Re: Cyanide copper tarnishing
Just a few other thoughts, is your air supply dry? If not you are mixing the condensate water with your laquer. Do your parts come out of a hot D.I. final rinse? Are you unracking barehanded coming out of the plating process? This can be a problem because the ph of the skin contact could be starting this oxidation, it is best to use clean plasticized gloves.
Re: Cyanide copper tarnishing
Assuming that the post treatment are observed religiously why don't you check on the pretreatment side. How about the etchant? Is this strong acid? What base metal your parts have? Please let me know. When you are solving the problem you have to understand where your parts went through.
Staining or tarnishing will show after a couple of days, that's true! When parts are soak in an acid it will simply remove oxides and scale but partly will also create some porosity and tendency of which is to give way to the chemical solution to penetrate deeper on to the small pores thus creating stains even you wash it completely,
So the best thing to do is to make use of a sealant to seal all porosity before processing. Say Loctite Resinol 90C
