Gold-bearing Colours

2720, 2740, 2745, 2755, 2810, 2820, 2825, 2830, 2835, 2837, 2838 & 2839 are gold-bearing colours which, if used directly on copper, frequently turn opaque, The colour red is created by colloidal gold. The copper oxides which are taken into the solution of the glass collects on the colloidal gold. Several firing are required to dissolve those oxides back into the glass. There must be sufficient glass for this to occur. This is why a second coat may be required after the first firing. If the colour shows no sign of clearing after two firings, increase the time, NOT the temperature.
All of the gold-bearing colours are clear on gilding metal. When used over another enamel they tend to be more pastel and less intense as a colour except for 2755 and 2835.

Note: working with transparent reds may bring you some unexpected results and may leave you with more questions. That is why an extensive article on this subject appeared in GLASS on METAL, the journal of the ENAMELIST'S SOCIETY, in the April 1994 issue.