[acidrain]

RedRiver, I agree with your explanation, except if it is a mixed alloy batch. Mixed batches will always have variations of color depth, and even hue to a degree. You would have the same variations if they were ano'd separately, so it's not worth worrying over. You'll simply have to adjust the color with dye times as discussed in previous threads. I digress.

To answer your question, there is a way around measuring surface area... I haven't measured surface area for quite some time using a modified CV ano method. Caswell has suggested I write a procedure for this, but I've been reluctant to go outside of the CC method as I suspect there will be many questions or problems associated with tank variables, but here it is in a nut shell:

First and foremost, you absolutely have to maintain repeatable ano conditions. This means exact tank temperature, known alloys, good agitation, and use a CC/CV power source.

With your tank temp exactly as you wish (I use 68F), ano a known alloy sample (same as the parts to be ano'd) of exact dimensions. I use a 6x6x1/4in piece of 6061, since I ano mostly 6061. Calculate the required amps at the CD you wish to ano at. Run the part in CC, and carefully graph the volts curve.
Study the volts curve, and note the beginning volts, and how long it takes to stabilize. Mine stabilize fully within 5min at 13.1 volts.
Now you can start your odd shaped parts run in CV (amps knob all the way up, Volts knob slowly adjusted to volts) at your "normal" volts (keeping the tank temp exact, and using good agitation). Continue the run in CV just for the beginning time period (so the current stabilizes), then note the amps at the end of the stabilization period.
Here is the modified part... start out in CV, but switch to CC for the remainder of the run after the current stabilization period:
With the power still on, slowly turn down the amps knob until voltage just begins to drop (or CC power light comes on).
Now turn the volts knob all the way up. Final adjustment of the amps knob to get your "normal" volts may be required after messing with it.
This adjustment method will seamlessly switch from CV to CV.
Finish the run in CC without further adjustment of the power for the time calculated to give you the millage at the CD you calculated in your beginning experiments.
The volts curves can be graphed for all of your alloys, then the appropriate beginning volts for each alloy can be used.
Periodic re-checking your numbers may be necessary, as tank condition changes.
Make sense?