Michael Ng
35
The 5131 and 5231 are actually different kind of enamel,
if you use a good loupe to look into the enamel of 5131 or 5231, you will see some little bubbles...

This won't happen in the traditional mineral or glass enamel. But since the last enamel material mining factory in Geneva closed in the late 70's, most of the traditional enamel material/colors can't be found anymore...