I have a handguard that I would like to anodize the outer part only, and leave the inner part anodized black.  Is this feasible?  

My idea is to protect the inner surface with foam pipe insulation, then media blast the outer part to strip the black anodization.  Then I will anodize the outer surface a different color.  Will the original black survive my re-anodization?

All thoughts welcome.

Vettepilot

Usually anodize goes through an etch process before the actual anodize to strip and help clean the material. If there is a way to "mask" off the area you don't want anodized, it could be possible. I used to work in the anodize process a long while back. We used to use rubber plugs to mask off holes that we didn't want any anodize to get into, but I don't think that will help you in this case. Things may have changed since I worked in the process.

The anodized part you want to preserve may actually work in your favor - when I've had parts masked off, a coating of iridite/alodine was created on the raw aluminum to allow the masking to adhere better.  I would imagine that the existing anodized coating would act in the same way.

Yeah, maybe I should forget the "partial" idea.  To do it, I would have to leave out the etching step on the handguard, as the etching process would attack the anodized area.  So I would have to rely on just a good cleaning of the handguard, then anodize.  I want to anodize the upper receiver, the lower, and the handguard a copper/bronze color.  If one of the pieces has a different prep procedure, the color and finish might not match.  I think my idea of trying to keep the inside of the handguard black is not a very good one as I think about it more...

Vettepilot

Anodizing is hard to match colors especially colors like gold, copper, or bronze. If you want the upper, lower, and hand guard the same color have all three dripped at the same time in the same batch of anodizing.

I went through this years ago on a large machine a company I worked for was designing. They wanted the trim parts gold, I worked with a friend of mine that owned a plating shop and no matter what he did only way to get the gold to all match was dip all the gold parts at the same time in the same batch of chemicals.

Also, if any of the parts you are trying to anodize are cast aluminum, it will not look very good when its finished.