Soft metal Kabutomushi aka Japanese Rhinoceros Beetle menuki.
I am sorry but I am not sure what they are made of. My best guess would be shakudo with parts that lost patina long time ago, and now the patina grows in the previously damaged areas. That is why colour on the surface is shiny black and red with many tones in between.
Made in edo period.
Size:
Omote: 41 mm x 24 mm
Ura: 43 mm x 21 mm
