Zinc plated part turning dark after blue chromate

[gplracer]

Thanks for responding to my question. You know how the parts have an irridescence or rainbow look ot them after they have blue chromate applied to them? It is like that but much more intensified. I see yellow and purple. I only put it in the blue chromate for 15 seconds. If my caswell plating solution...

[gplracer]

I got my Caswell zinc plating kit 6 months ago and have had nothing but success! The parts look great. I have not plated anything in around a month or so. Now the parts come out looking great but when I dip them in the blue chromate for 15 seconds they are turning dark. Any ideas on what this could...