Considering the other thread where you
first posted your problem, I'm not sure now what you're seeing in your "dull grey" parts. Can you post any photos of your parts?
All parts come out of the plating bath w/ a grey/brown film on them. The only way to get rid of it is a post-plate acid "bright" dip. Are you doing that?
Chromates are all acid based, but don't "self-brighten" as much as you'll get w/a separate post-plate dip.
Does your agitation pump have a built-in filter? If so, you're filtering out all the brightener.
Your temperature & current should be just right now, and you
should be getting fine bright parts. But clearly something is still not quite right. You
should not have to manually polish parts after plating to get them bright.
Check the new photos in my photo album.
Zinc Plating Album
I didn't have to do
anything to those parts after plating. The way you see them is the way they came out of the plating bath & chromate.
Of course, preparation is most important. Beyond that, this is the procedure I use:
- acid pickle (10% muriatic acid solution) - I only do this if the freshly cleaned part has been exposed for more than a couple of hours. It activates the steel surface, and etches away any minute rust which might have developed since the part was cleaned/blasted.
- plate - I use .140 ASI & 100-110º, no problems at all
- acid bright dip - depends on final chromate
- for clear or yellow chromate, I use 1% nitric acid, it is far superior to any other acid in "brighteneing" effectiveness. Nitric is difficult to obtain, and much more expensive if it has to be shipped. 5-10% Muriatic acid works good, but the part must be dipped a bit longer.
- for Black chromate I use 5-10% sulphuric acid. Sulphuric is the only type to use w/black chromate.
- Chromate
Sean