10 Gulden 1935 - Environmental Damage

I agree: it does not really matter if the corrosion substances have been removed or not.

The damage has already been caused by the corrosion.
Fortunately, in this case, the damage is only very little.

It is an attractive coin anyway!

My copy of Krause:
KM# 159
Danzig, 1935 10 gulden, nickel (I presume pure nickel).
Mintage: 380,000.
Krause lists value at
XF: $1,259
Unc: $3,750
BU: $7,000.

I have no idea why a coin with such a large mintage should be valued so high, but I notice that all of the Free City coins of Danzig of this period have a high value.
Perhaps? they were not issued, or perhaps? all were withdrawn from circulation, and almost all were melted.
This is one of the survivors.

Two considerations:
1. Careful thought need to be taken, before any action is decided upon.
2. On (my) presumption that the coin is pure nickel, the ability to resist corrosion is important. Is the coin magnetic? (pure nickel IS magnetic, copper nickel is not).

Action to be taken: NONE!
Why?
Especially with a coin of this value. (1.)
Pure nickel is a bit like aluminium. If you scratch it, a fresh atom thick oxide layer instantly forms, which protects the metal underneath. (2.)

Your answer is war. In 1939, Gulden was exchanged for German mark, so it can be assumed that a significant proportion of the coins have been melted. In Kopicki from 1995 (the most extensive and probably the best catalog of Polish coins) this coin has R5 (26-126). Today it is known that there are more of these coins. I think R2 (3001-15000). Of course, I wasn't going to do anything with this coin. I was just wondering if I remove coin from grading, the corrosion would not increase with time.

I will be surprised if this coin does not sell well above the Heritage estimate of $1200-1500, since it just sold in September for $1900, and there are a lot of high selling prices for better grade examples like this one.

Good luck if you are bidding on it.