It is hard to say if the problem you are experiencing is the same as ones I have seen or not, but it sounds like it may be. If you can post a good picture or two, it might help.
I’ll start by asking some questions that could help diagnose the problem.
1) What current density are you using, and are you sure of the surface area and how to calculate the required current?
2) What is the surface area?
3) What kind of power supply?
4) What acid concentration?
5) How are you prepping the part before anodizing?
6) How are you connecting the part to the current?
7) What is the starting anodizing tank temperature and ending temperature?
8 ) What temperature is the dye?
9) Did you use distilled water to mix with the dye?
10) You first said the discoloration wiped off, is it always like that, and does it wipe off easily, or does it take some effort?
11) When you are finished dying, and you rinse the part off with clean water, does it look like a brown-black, or a blue-black, or a deep dark black while it is still wet? Be sure to look at it in good light, and compare it side by side with other blacks to be sure, as a lot of tones look black until you compare it to a real black.
12) Is the whole part evenly rust colored, or are there patches or patterns that follow the shape of edges, etc.?
If the part simply wipes clean, it could still be an anodizing problem rather than a dying/sealing problem. If some of the important parameters are off, the anodize layer can be “wrong”. It could be the pore size is too large or small, and it could be the outer portion of the anodize layer is too soft and the top of it wipes off, leaving an underlying portion of it that is better. You could probably liken it too polishing old deteriorating chalky paint up to restore the proper color. If the anodize isn’t “right”, you can get rust tones (or reddish, brownish, etc.) from the black. I believe that is because some of the colors in the black are more readily held by certain pore conditions.
One possible cause is that the anodize layer is marginal because the actual current density is out of range, perhaps too low. So, you should be certain that the electrical connections are excellent. If that doesn’t help, you might try doing some tests with 15-25% more current.
I you are using tap water for your mixes, that is a possible problem. I’m sure some tap water is good enough, but a lot of it isn’t.
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