Casein identification guide: casein is a thermoset semi-synthetic polymer made from milk, hardened in formaldehyde
13. Hot needle test: slow to burn, heat aura appears around point, sizzles, smokes, smells like burned milk, usually leaves a hard ridge around test point.
source: Button Materials A-Z: Identification Guide
by Jocelyn Howells
The above is based on the National Button Society's Classification System.
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