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Cranberry glass or'Gold Ruby' glass is a red glass made by addinggoldsalts orcolloidal gold to molten glass.Tin, in the form ofstannous chloride, is sometimes added in tiny amounts as areducing agent. The glass is used primarily in expensive decorations.[citation needed]
Cranberry glass is made incraft production rather than in large quantities, due to the high cost of the gold.[1] The gold chloride is made by dissolving gold in a solution of nitric acid andhydrochloric acid (aqua regia). The glass is typically hand blown or molded. The finished, hardened glass is a type ofcolloid, a solid phase (gold) dispersed inside another solid phase (glass).[citation needed]
The origins of cranberry glass making are unknown, but many historians believe a form of this glass was first made in the lateRoman Empire. This is evidenced by theBritish Museum's collectionLycurgus Cup, a 4th-centuryRoman glasscage cup made of adichroic glass, which shows a different colour depending on whether light is passing through it or reflecting from it; red (gold salts) when lit from behind and green (silver salts) when lit from in front.[2][3]Kitab al-Asrar, an Arabic work attributed toAbu Bakr al-Razi contains one of the earliest descriptions of the preparation of gold ruby glass.[4][5]
The craft was then lost and rediscovered in the 17th centuryBohemian period by eitherJohann Kunckel inPotsdam or by theFlorentine glassmaker Antonio Neri.[citation needed] Neither of them knew the mechanism which yielded the colour, however. Chemist and winner of the 1925Nobel Prize in ChemistryRichard Adolf Zsigmondy was able to understand and explain that smallcolloids of gold were responsible for the red colour.
The most famous period of cranberry glass production was the baroque era.[6] Later, cranberry glass was produced for example in 19th centuryBritain during theVictorian Era.
Cranberry glass creations were most popular as a table display, often holdingcandy orflowers.[citation needed] Cranberry glass was also frequently used for wine glasses,decanters, andfinger bowls. Cranberry glass was also well known for its use in "Mary Gregory" glass.[citation needed] This glass had a whiteenamel fired onto the glass in a design, usually with a romantic theme.
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