20 Francs 1953 B - Damage?

In the process to check some coins to add them later to my swap list, i found this one.

First, what called my atention was the damage in the portait, but for what i come here is for the damage in words"Liberte Egalite".

I tend to think that the overall damage in the coin was done with some kind of corrosive product (?) but that doesnt explain (for me) why several letters from the leyend are like in two "levels".

In other words, becasue that corrosive product, ¿letters just should have been "deleted" like if the coin was worn?



Some detailled photos about the damage in the leyend i told before (you can also see thoose 2 "levels"):

the top of the letters look like reduced in height the same as the field is. not deleted entirely but reduced.

it is some interesting damage, and maybe two different mechanisms. one made the many tiny pits on the obverse (and some few on the reverse), and another made the lower level under EGALITE

Thank you for your input Mr. Midnight.

I am going to keep it with me as a curiosity, maybe in the future i will try to search more about this.