Casein: fish scale pearlized, England, sew-through

Background/Story

This button is a press-molded wafer. Back marks are uncommon in casein buttons.

Casein identification guide: casein is a thermoset semi-synthetic polymer made from milk, hardened in formaldehyde

7. Many pearlized caseins, made by mixing fish scales into the plastic batch.

source: Button Materials A-Z: Identification Guide
by Jocelyn Howells