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Hydrogen release, zinc plating heat treated parts

We are currently testing to run zinc plating on fasteners that have undergone heat treatment, specifically sheet metal screws, self drilling screws, etc. We have tested oven baking for hydrogen release but the finish is not as clean and shiny as if we had not gone thru the oven. We are currently going to the zinc plating tank and then rinse, after this we set the zinc with a 0.5% nitric acid and then we go to the oven for 3 hrs. at 400 °F After the parts have cooled we edge them in the 0.5% nitric acid we rinse and seal. With this process we get dull uneven looking parts. How can I get a shiny finish, like what we usually get from large warehouse retailers of fasteners. We tried going back to the zinc bath for 10 min. after baking in the oven and then follow the normal zinc plating process and the parts look very good. Is this normal practice for hydrogen release process. What can be recommended to get a good looking part.

Hector Flores
plating shop - Monterrey, MX, Mexico
2004