Step 6: Anodizing

(Translated by googl-translator)

Since all materials that can be used have poor weather resistance and form oxide layers in contact with oxygen, the sound bars must be anodized. Unfortunately, all of the materials mentioned are largely unsuitable for decorative anodizing.
Before the actual anodizing, the parts are pickled in an alkali. Depending on the length of time it remains in the pickling solution, there is a greater or lesser amount of material removed from the surfaces.

Then the actual anodizing takes place in the electrolytic process in sulfuric acid or oxalic acid electrolytes with the application of a direct voltage. After anodizing, the dyeing and then compacting takes place in a hot water bath. The duration of remaining in the compression bath depends on the anodized layer thickness generated, i.e. on the duration of remaining in the anodized bath.

Since we cannot carry out this process at the university, we did not have 100% control over the process. We tried with the company to make the material pickling and the subsequent anodizing layer as thin as possible in order not to get any sound changes due to the anodizing.

For the most part, this worked very well, only the time in the compression bath was a little too short, so that the paint is still a little bled out in some places.

Overall, however, we were only able to determine small changes in the sound spectrum due to anodizing for the red plates.

Since we were not sure about it at first, we had reserved a lavish subsidy for retuning.
We tried several colors. For example, the color blue had to be anodized significantly longer for an intense color, which resulted in greater changes in the frequency spectrum than with most other colors.