The opaline series G-160-168, & G-190 employ compounds of phosphorus oxide as the opalising agent. The glass is a little like an emulsion where phosphate enriched droplets are dispersed throughout the glass matrix. With a lot of heatwork of the kind involving solid sculptural work or multiple fusings or even murrine work, the droplets increase in size and number until the matrix changes in expansion and may become incompatible with the base clear glass or other colors. The increase in the size of the droplets or crystallites with much heatwork and time are a natural physical manifestation of these glass structures.
Keeping lip wraps of opaline going all day in a warmer may cause problems.
The opaline series has been developed to offer a simple flashing range with minimal opalescence. It is ideally suited to lighting or blown work that doesn't require very long working times and heat cycles.