Terbium glass is a high refractive index glass used as a coloured gemstone simulant. Dopants are added to the raw Silicon Dioxide to create every colour imaginable.
Glass gemstones are cheap to produce. When added to glass, metals and minerals can create many colours. To date we have access to over 200 colours, with trends often seeing new exciting colours being produced.
Additives, besides giving colour, also have other effects. Lead is added to raise refractive index (sparkle) . It also makes the material more durable by increasing its specific gravity, a feature characteristic of lead crystal glassware.
Since amorphous glasses conduct heat much faster than gems, they will feel warm to the touch, much warmer than most of the gems they may resemble. When viewed under a loupe, bubbles can sometimes be seen inside the gemstone.
