For many years Bright Gold & Platinum have been used for decorating glass and glazed ceramics. The application and firing of bright gold is reasonably simple. The ware should be perfectly clean and dry. Dust and dirt should be avoided as much as possible to pre¬vent impurities on the fired film.
Use the gold as supplied - it is not necessary to shake the bottle before use. The most popular way of applying gold and platinum is with a soft brush and the decorator thus has the opportunity to apply lines, bands or freehand patterns. The brushing properties of the liquid metals are such that the correct deposit is obtained without undue spreading. At the same time it should not be applied so thickly that there is a tendency for the film to run down during the firing. It applied too heavily the gold or platinum will tend to fire out with a scummed finish and may even blister on. If applied too thinly it will have a purple tint after firing. It is often worth keeping an unfired sample for reference so that it can be compared with the fired results.
In firing, it is essential to have good ventilation which is best obtained by leaving the kiln door open slightly until the gold has "smoked off", and this will be achieved by the time the kiln approaches a dull red heat. Without adequate ventilation the metallic film will fire out giving a finish which is neither attractive nor durable. This is particularly evident when large quantities of pieces are fired close together. If difficulties of this type are experienced then the rate of firing should be slowed down and the ventilation increased. Earthenware, china and porcelain should be given a firing corresponding with the hardness of the glaze. If under-fired the metallic film will wipe off and if over-fired it will sink into the glaze and look dull or cracked.
The ideal firing method and temperature for gold and platinum in any particular kiln is the same as for hanovia Lustres and is best determined by experience. The following temperature ranges will be useful as an initial guide.
Bone China 680-760°C