Acidrain is quite right.
Since Xtal01 is looking to Hardcoat a piece 0.56 sq.ft. (I visit other websites too) I can provide some approximate numbers.
Using Acidrain's ASF figure, figuring on 7075 alloy, and a coating thickness of 3 mils:
DC current; 17A
Peak voltage 29VDC
Anodizing time; 72 min.
Average power dissipaton in the tank; 320W
These figures assume PERFECT electrical connections. The voltage and power can be much higher if they're not.
The cooling problem is not getting the electrolyte cold enough, but its keeping it in a narrow temp range for the full 72 minutes, with the mentioned power dissipation. You will fail if you don't, and we haven't even mentioned the very vigorous agitation required.
Assuming you actually formed a Type III layer, dyeing it will be problematical, you probably want it jet black, right?
Other than true milspec M-16 lowers that have to pass govt. specs for govt. procurement, commercial lowers are more likely a Type II layer grown to 2-3 mils thick. The dyeing is too good for it to be Type III. Yes I know what you have read on the internet. Claims of a Type III coating are easy to make, it takes a well equiped test lab to tell the difference between Type III and Type II grown to the same thickness.
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