Glass that made to look as precious natural gemstone

Glass production involves melting acidic oxides, commonly silica in the form of sand, and cooling the melt rapidly to prevent visible crystal formation. Various oxides like boron, antimony, phosphorus, soda, and lime can be used to alter the properties and composition of glass. Opal glass is produced by adding compounds like calcium fluoride and aluminium fluoride, among others.
Glass's composition and properties vary widely, and its color is influenced by impurities such as iron, which can be countered by adding decolorizing agents like manganese or arsenic salts. Glass can also be intentionally colored using metal oxides-iron oxides for brown and red, copper for blue, cobalt for blue, and others for a range of hues. Gold can be used to achieve a ruby-red color.
Imitation precious stones are often made from glass or other materials. "Doublets" combine a quartz or mineral crown with a glass base, while "triplets" may include painted layers for color. Modern composites use combinations like weakly colored beryl with colored paste or transparent cement to imitate real stones.
Synthetic stones, due to advancements in production, are now high quality and reduce the need for complex imitations. Plastics such as methacrylic and aminoplastic resins are used for imitation due to their ease of molding and sharp edges, though they are distinguishable by their lower density, hardness, and thermal conductivity compared to real stones. Imitations of opaque gems like turquoise and jade are less lucrative but still practiced, often involving chemical growth methods or layering techniques.
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