I grabbed this on eBay a while back for $20 or so, and I've been a little worried about the authenticity about it, since the seller didn't normally sell these sorts of coins, they didn't have much information on it, and I got it for what seemed to be reasonably cheap. Unfortunately, I don't have a scale to weigh it at the moment, but I was wondering if anything about it looks fake to anyone here.
I don't collect pre-Meiji coinage, and deny any expertise in authenticating them. That said, both sides of your coin appear to match the Kaei Isshugin listed as #09-53 in the Japanese Numismatic Dealers Association Catalog. That 1.89g .968 silver coin was produced from 1853-65, late in the Tokugawa Shogunate period. The catalog picture (stated to be actual size) measures ~9.5x17mm. In the Japanese grading system I would call it a "naka" ("middle") grade, valued at ¥2,500-17,000 (~$26-178) depending upon which of 7 slightly different varieties it may be. Total mintage is given as 159,244,800, without any breakdown of the types. Both Japanese Coinage by Jacobs & Vermuele and Coins of Japan by Munro, agree on the initial issue dates. Jacobs only describes two varieties, differing slightly in the shape of some of the stroke endings, without stating the end of the issue period. Munro doesn't mention any differences, but gives the same start/finish dates as the JNDA. I see nothing to question its authenticity. Edited to add: Big surprise! Krause disagrees to some extent with the Japanese authorities. C#12 has the same specs I've quoted above, but a C#12a is listed with a reduced silver content and gross weight - 1.88g of .880 silver. Values in the 19th Century 3rd Ed. (2001) are much less with F/VF at $8-12 for C#12, and $15-22.50 for C#12a.
