Opaline #300 is a striking colour much like Gold Ruby #221, except that instead of developing larger metallic gold agglomerations when heat treated at a certain temperature range, the particles created are lead phosphate droplets. As they grow in size and number they interfere with transparency. The outcome is varying degrees of a white semi-translucency or dense opacity.
We provide the raw material in a transparent state where the opacity potential is latent. It is doped with a very small amount of Neodymium oxide so that we can differentiate it from Clear #210. It requires heat treatment at a certain time and temperature to develop degrees of opacity.
Run the glass into the mold at the usual temperature as the rest of the casting range i.e. 800-850°C (1470-1580°F). Then lower the temperature to 620-650°C (1150-1200°F). Hold at that temperature for at least 15-30 minutes. It is difficult to give an exact prescription of holding times and temperatures because of the individual parameters of the kiln, thermocouple position, thermocouple accuracy, and mold thickness. It is a good idea to experiment on a small scale to begin with –ideally with samples that can be withdrawn from the kiln at striking temperatures and visually examined. Opaline effects can be achieved ranging from translucence (much like the look of Lalique) through to a dense white opal, depending on time and temperature. There will be different response times depending on whether you are using billets or frit.
There will be a limit at which the Opaline/Opal phenomenon can be achieved by watering down the glass with other colours. Try no more than 3 parts Opaline to one with any other colour when mixing in a reservoir.