[acidrain]

I've never had foamy black dye, but I have had the bubbles leave un-dyed areas. I don't have agitation in my dye tanks, but I manually swish the parts around in the dye, and that has cured the bubbles/un-even dyeing. I'm thinking of adding agitation.
Could it be a math mistake? The surface area is actually more than calculated?
A good base line to go by is to run an exact size of a known alloy plate, and observe the volts for a given CD.
Then, while anodizing, if you see the volts higher or lower, it will be a clue.
Actually, I've done this with 4 alloy types, and as long as you know the alloy of the parts you are anodizing, you can ano in CV mode. I haven't measured surface area in over a year, and have very consistant results. This also cures the problem of different colors on different alloys.
I wouldn't recommend this without good temperature control, base-line experiments, and knowing what alloy your parts are.
If you did this experiment with some 6061, and dyed it as well, it may help determining if the dye is still good.
If you want more info on this method, PM me.