For most of history, the opal was one of the world's rarest gemstones. The stone's rarity meant that the opal was accessible only for the elite, so when an opaque milky white glass was developed, opal fans were eager to get the look. It was a complex process where glass containing tin, arsenic or phosphorus oxides were carefully cooled and minute particles separated out giving the glass a milky appearance. This Victorian opaline glass and white paste cluster collar is an outstanding example of the style.