The technique: painting a layer of either black or white liquid enamel onto the copper, firing, painting the opposite liquid colour (ie white on black, black on white) and then sifting a third colour over the top.
Scratching out a design, firing, sifting a fourth colour over the top, firing, stoning down to smooth, then firing again to bring back the shine.
I think the colours worked out better when the black layer was the first, with white on top. You can see that they are the brighter ones (the top two, and the bottom two on the right)
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