how can you tell when old anodic coating is completely gone?

[Chunkstyle]

hey --

i'm going to try a home-brew red anodizing job on some aluminum bmx brakes. i used sodium hydroxide (drano) to strip off the old gold ano. worked well -- a bit slower than i'd expected. however, when trying to polish the bare alum in prep for the new anodizing, it's not polishing up real easily -- like there may still be some hard alum oxide present from the old coating (i'm assuming that all needs to go before re-anodizing). usually, when i'm polishing alum, it "mirrors up" pretty fast. in this case, it's kinda slow going. how can you tell if the old oxide coating is completely gone? does the old dye coming off signify that, or is there more to it than just that?

i'm leery of soaking the parts in the caustic bath for too long.

i'd appreciate any info anyone could offer.

thanks!

[sswee]

The color goes before all of the anodize. The easiest way to check is with a multimeter set to ohms and check for continuity around the part. If you get continuity without having to scratch into the part with a probe point, you should have the old coating off. With some experience, you usually will be able to tell by the look of the part when it comes out of the stripper and is rinsed off.
SS

[destroyer125]

if it isnt all completely gone, I would just strip it some more.