Belgium1 Franc 1942- Léopold III BELGIE-BELGIQUE with bumps [solved]

Belgium1 Franc 1942- Léopold III BELGIE-BELGIQUE with bumps
4.4 g weight (a little heavy)– 21.5 mm dia. -2.0 mm thickness ( a little thick)
My thoughts: Gas bubbles (only one side)? Pattern coin? Morris code?
What be your thoughts?
Photos with different light shots:

I've seen a similar Romanian zinc coin once. No clue what's with it.

Any raised areas or bumps would have been pressed smooth at the mint when the design was stamped into the coins top and bottom at the same time. Maybe I am wrong? Ed

Rusted Dies
Dies which have been damaged (pitted) through corrosion. The "rusted" areas of a die create raised bumps on the coin during the striking process, thus giving the coin a flat or dull appearance.

http://amhistory.si.edu/coins/glossary.cfm

Other examples of something like this happening to zinc coins:

https://en.numista.com/forum/topic25447.html
https://en.numista.com/forum/topic35507.html

Quote: "g00n"​Other examples of something like this happening to zinc coins:
​
​https://en.numista.com/forum/topic25447.html
​https://en.numista.com/forum/topic35507.html

Close pattern - but - my coin has the bumps only on one side? Interesting. Ed

​

It seems to me more some kind of corrosion working its way from the inside out. The similarity between the bubbles on your coin and on the coins in the threads cited by g00n is striking.
Rusted dies are unlikely to yield such nice details on the one hand and such strange bubbles on the other.
It's also peculiar that all examples we have are zinc coins.

Just found this - opposite of the one I have

Zinc-pest works on the inside normaly seen from the outside as white spots and expands the crystal structure enormously. Don't know why only one side has those bumps maybe a pruction process were one side gets through more stress then the other and got micro fissures as a result were the "pest" could get in more easily.

Zinc pest, is a destructive, inter crystalline corrosion process of zinc alloys containing lead impurities. It was first discovered to be a problem in 1923. Zinc pest affects primarily die-cast zinc articles that were manufactured during the 1930s, 1940s, and early 1950s. In Germany, articles made from Zamak during World War II and several years thereafter may be affected. Purer alloys were not available to the manufacturers as they were used for the war effort, or were just not on the market after the war. While impurities of the alloy seem to be the cause of the problem, environmental conditions such as high humidity may accelerate the process. Also, significant temperature changes can be damaging. Affected objects may show surface irregularities such as blisters or pitting. They expand, buckle, tear, and in the end, crumble. The irreversible process will eventually destroy the object. Due to the expansion process, attached normal material may be damaged secondarily. Zinc pest is different from a superficial white oxidation process that may affect some zinc articles. Zinc pest is dreaded by collectors of old model trains, toys, or radios where the zinc die-cast process was used.

Hm ... I thought the oxidation/corrosion was also called that ... then its not the same or I got my facts mangled.

Quote: "Idolenz"​Hm ... I thought the oxidation/corrosion was also called that ... then its not the same or I got my facts mangled.

​From my research I believe Zinc Pest is the corrosion from within and White Rust is corrosion from exterior.

Zinc when exposed to the elements will form its own natural self patina layer, and even when scratched will self heal; this process will vary from location to location and can take many years.
For zinc to form its own patina it needs to be able to get regularly wet and then dry, if however, it gets wet and the water is allowed to rest on the zinc, White Rust will form. The first sign of White Rust occurring on the surface is a white stain which may increase to a white powder. If this situation persists the White Rust will eventually corrode through the zinc and holes will appear.