I'm nearly at the end of my wits. I have been anodizing using the LCD method for about 2 months now. When I first started, I had no problems with consistency. Parts that were anodized took color well and were great. When I first converted, I used my existing electrolyte and just watered it down to get close to the LCD concentration. After about 10 batches without problems, I decided it was time to get a larger tank (which I had been wanting) and make a fresh electrolyte bath. I used a 30 gallon rubbermaid tote as the tank and prepared 15 gallons of electrolyte solution according to the LCD instructions.
My power supply is a 5A, 30V lab power supply that can run in CC or CV mode. Obviously, I use CC for anodizing.
So, with the new setup, I'm getting about 50% of my parts to turn out correctly, and I'm getting really tired of stripping and re-anodizing parts. When parts are good, they're great. Here's a pic:
However, when parts do not turn out well, they always have spots on them that do not dye properly, as in the pic below: (you may notice that there is some etching on the part... that's not the problem, the problem lies in the large discolored areas...)
I don't have this tank set up to measure PAR, so I'm anodizing according to the LCD instructions, 4.5 A/ft^2 for 90 minutes. Dyeing is done in Stainless Steel pots on the stovetop. Sealing is done in boiling distilled water in a SS pot.
Initially I thought these problems might be caused by bubbles sticking to the surface, so I tried adding an agitation system to the tank. It does not appear to help, as I'm still having the same problems with or without agitation. Here's a pic of the agitation system in action:
My last possible idea is that this may be something left on the surface, some sort of grease or something. I do not use Caswell desmut, I simply wash the parts in hot water/dish detergent. Does anyone else have any ideas to help me out? I'm stumped here.