Black Anodize Residue ?

A. I would tell the anodizer that this smut is unacceptable and that if he considers it normal he should wipe down the parts before he ships them to you so that when you test them there is no residue. In the worst case he will wipe them down; in the best case he will fix his operation so that he doesn't need to. Regards.

A. It is probably smut, but if the cloth has any solvent on it, some dye will come out on it.

A. If it's wrought material there should be no solution bleeding, if its a casting material, no matter how hard you might try, there is going to be some (you can minimize as much as possible) but there will still be some entrapment of the dyes and or the sulfuric. Basically if its not a colored film that is coming off its more than likely a seal bloom that also can and should be wiped off before shipment.

A. It is not normal with well processed parts, other than potentially castings as Mr. Stiltner pointed out. There are potentially a couple things at work; an amorphous coating caused by anodize solution temperatures being too warm, too fast of a ramp, etc., this would occur prior to the dyeing step, dyeing/seal solutions not being rinsed properly, or the dye not being completely sealed in. Perhaps a cold seal that requires some curing time such as NiF is being used for example which is a popular commercial seal, versus hot NiOAc which I personally think is best for dyed articles. I have seen fishing reels and parts at one shop I worked, which exhibited what you are describing and it turned out to be the anodize parameters, both temperature,ramp rate and voltage/amperage cycles. Until we figured it out, we were paying racker/packers to wipe every part. Expensive! One note, sealing bloom does not wipe off. I would start with insuring that the parts are completely sealed first using a dye stain test or some such.

A. The seal test is ASTM B136. We need to know the alloy, free acid, dissolved aluminum, temp, current density etc Meanwhile, try a 5% nitric acid dip between anodizing and the dye like anodize, rinse, 5% Nitric, rinse, dye. Try it in a bucket first, let us know.

Q. In this case of smut appearing after sealing (but possibly caused by one of the previous steps), how should a 5% Nitric solution prevent the smut? I.e., why could that solve the problem?

A. Following anodizing, the pores are filled with sulfuric acid and "white" aluminum sulphate. The mere rinse only dilutes off the surface, not the pores. 5% Nitric Acid helps flush the aluminum sulphate out of the deep pores, otherwise, when you hit the HOT seal the aluminum sulphate pops out as a smut (it may be dyed black).