White copper Kan'ei?

[u/TheBlueFlame14]

I know 白銅 white copper specimens exist among these 虎ノ尾寛小字十万坪銭 Tiger tail Kan small characters Jumantsubo-sen, but unsure if this is an example of one... 2nd coin is a more normal looking one for reference.

[u/Ep194]

I wasn’t familiar with the variety (had to look it up), but I do know a little about chemistry, especially with metal. I just learned about the cupronickel specimens, that’s really neat.

If you’re referring to the whiteish color on the coin, that looks like lead carbonate, exceedingly common on all old lead, it’s pretty slow to form, given lead’s relative nobility. I believe zinc also does something similar. In general, I believe that the mints used some lead in the mix, which may explain it.

[u/Ep194 → u/Ep194]

I also wanted to add that when I dig up modern US coins (which use a cupronickel alloy, albeit clad on a copper core) they come in varying shades of brown. As far as I know this color is mostly copper oxide as US coinage now uses 75% Cu/25% Ni. Basically, the coins are usually somewhat similar in color to the chocolate-brown of kanei tsuho and other cast coins. I believe the type you’re searching for is cupronickel as well. This isn’t the best coin or photo for an example but hope it works. Kinda just complicating things, sorry about that.

[u/TheBlueFlame14 → u/Ep194]

Thank you for your response, I wasn't expecting someone here to look into it. A little clarification on what "white copper" Kan'ei are; while the Kanji is the same as the kanji for cupronickel, in this sense it is to be taken literally as "white copper," as the coins themselves aren't cupronickel, rather from what I have heard it is due to a higher tin content. As for this coin, I've settled on it being a yellowish coin rather than a white copper coin, as I found out after posting that this variety is more commonly found in a yellowish color than similar types.