Copper, silver and gold have been used to create lustres - a metallic sheen - on or within ceramic glazes from the earliest beginnings of the technique.
Lustred ceramic making began in the Middle East over a thousand years ago. It would appear from the earliest known pieces that the initial intention was to give ceramic objects the appearance of solid gold or silver. It would seem likely that finely powdered metals would be incorporated into the unfired glaze mixture to be fused into the molten glaze during firing. This could work if precisely the right conditions were met during the firing. However, these conditions are pretty exacting. If a glaze containing the metals were fired to maturing point and merely allowed to cool naturally then a disappointing whitish or grey stain would result, or green in the case of copper. The metals would have been oxidized in the fire and to be converted back to the desired shiny metallic state `reduction `would be necessary – ie the atmosphere within the kiln…