Best anodizing guide?

[Zeeflyboy]

Fusion 360 but can't work out surface area for some reason.

I have 5L tubs. Only 3L of water plus added ingredients.
By weight I have 3000g of water and 400g of 85% acid. So that is 7.5% of 85% acid?

Rarely see suggested ratio by weight, usually by volume.

However, simple enough to figure out an approximation I guess. 3kg of water is 3L, for the sake of simplicity we'll say your 400g of 85% acid is actually 340g (400 * 0.85) and ignore the extra 60g of water, which when considering the specific gravity of sulphuric acid is 1.85 should mean it was about 184ml.

So you have actually got 0.184L acid to 3L water, or roughly a 1:16 ratio which is not too far off what I've seen recommended for 6asf (slightly low perhaps), but more than a little on the low side if using 4.5asf (caswell recommend 1:3 battery acid/water, or around 1:11 acid/water if my maths holds up).

That jives more with what you would expect - too low a concentration will give a smaller pore size which is bad for dying. Were you calculating with 4.5asf or 6asf out of interest?