Kozuka made of hiiro-doo, it is rarely used alloy of very pure copper. Its literal meaning is "scarlet copper", also know as shudoo. Produced only from a second half of Edo period untill Meiji period. It was made by specialised shops in a time consuming way. That is why it was rather expensive. (Alloy description from "Tosogu Classroom" vol. 1, by Fukushi Shigeo, translated by Markus Sesko)
Nanako ground, carved in takabori and decorated with shakudo inlay and gilded elements.
According to certification theme of the kozuka is shrimp from Ise bay, which english name is spiny Japanese lobster.
https://en.wiktionary.org/wiki/%E4%BC%8A%E5%8B%A2%E6%B5%B7%E8%80%81
Kozuka is signed "Masayoshi" with Kao. Based on the material used we know that it was made in second half of Edo period, however I do not know which "Masayoshi" made this piece.
When I got this kozuka it was in very poor condition. That is why it has been cleaned and some conservation work has been done. Pictures of the kozuka before repairs are at the bottom of the page.
Size: 98 mm x 15 mm x 5 mm