The anodizing is apt to be damaged, especially on edges, if you were to tumble them. The only instance where a tumbler can be of use on anodized part that I know of is in removing smut. I am assuming this is why you are asking about tumbling. If the parts can be gently tumbled for a short time, it can be successful in doing that. You would be more likely to achieve this with small, light parts, rather than larger and heavier parts that will be hard to do without damage.
In general, if the parts are smutty after the cleaning, anodizing, dying, and sealing process is complete, it means something is not quite right in one or more of those steps. Often the smut can be wiped off and the appearance is ok, but it's a lot nicer to give them a simple final rinse and end up with a clean bright part when dried. Here are a few things we have found will help, if not eliminate dirty and unattractive parts:
1) Rinse very well between every step. Don't allow cleaners and other solutions to dry on the part, this takes careful attention with heated solutions like the main degreaser-cleaner and de-smut.
2) Many smut problems stem from the anodizing process. If the acid concentration is too high for the current density, it will leave a less than perfect surface. If the tank temp is too high, smut is often worse. If the parts are anodized for to long, smut can become a problem. Good connections are very important to achieve good and consistent results. Don’t ignore the cathode connections. All of these problems can also cause uneven colors when dyed.
3) If left for to long in the dye tank, smut tends to be worse. Some colors do seem to need more time to dye to reach the desired color depth. Other colors are capable of reaching a dark rich depth in as little as 2 minutes, with 3-6 minutes being common. Agitation of either the part or the dye solution speeds up the dye process and helps to reduce smut. Dye solutions that are mixed too strong (not enough water) will aggravate smut troubles. One would think a strong dye concentration would dye faster and darker and help, but that hasn’t been what we have found. We have rather found that you only want the dye strong enough to reach the desired color in a reasonable time. If the parts are not dying well in 2-40 minutes, suspect the anodizing layer as being inadequate in some form.
4) When sealer is old, or parts are left in the seal bath for too long, smut problems worsen. When using nickel acetate as a sealer additive, don’t mix it too strong.
If it isn’t smut that you are concerned with, but rather the basic texture or appearance of the part, then different preparation prior to anodizing is the only way to correct that. That can mean either mechanical means such as sanding, polishing, or machining to produce a pleasing appearance. Also, the way it is prepped in the cleaning, and etching solution if used, can influence appearance. Usually when done correctly, the part surface qualities should look the same after anodizing as it did when fully prepped and just beginning the anodize process, except for the color change. It can get uglier if something goes wrong, but it won’t get better.
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