Application of Stammkennzeichen...

[Milos Gazdic]

Hello,

I am wondering if anyone could share some light on application of Stammkennzeichen / STKZ / origin code / ferry code... or how ever it should be translated to English.

Namely, we all know that these letters / codes were applied at the factories, during or after production and were removed by washing, sanding or overpainting on unit level (there seem to be examples of airframes that didn't receive any STKZs on the fuselage and wing's undersurfaces but that is for another discussion I guess).

My question is: What kind of paint was used for Stammkennzeichen?

As mentioned above I have seen fighter airplane where these codes were sanded off and those where they were overpainted and apparently some were washed off, which makes me believe that not all of them were easily washable / temporary but some might have been applied with permanent paint.

Is there an article, book's chapter, site or any other secondary or primary source explaining this part?

Thanks a lot for any info shared.
Best,
Milos Gazdic