Borax

## Borax Borax

**Borax** (sodium borate, Na₂B₄O₇·10H₂O; Lat. *borax* or *chrysocolla*) is a white crystalline salt that played an important role in metallurgy, alchemy, and the preparation of glazes and enamels. Known since antiquity and imported from Central Asia and Tibet, borax was prized for its use as a flux in soldering and in the assaying of precious metals—its ability to dissolve metal oxides and facilitate the fusion of metals made it indispensable in goldsmithing and silver working. Medieval Latin texts sometimes confused borax with other substances (particularly *chrysocolla*, a copper mineral used in soldering), but by the early modern period its identity and properties were well established. The *Probierbüchlein* and other assaying manuals describe the use of borax in cupellation and in testing the purity of gold and silver.

In alchemical practice, borax was used to prepare various metallic compounds and to facilitate reactions involving metals. Its ability to form glassy, vitreous substances when heated made it useful in the preparation of artificial gems and colored glasses, practices that overlapped with alchemy's interest in imitation and transformation. Paracelsian iatrochemists employed borax in the preparation of certain medicines, and it was used externally as an antiseptic and astringent. The substance's name derives from Arabic *būraq*, itself borrowed from Persian, reflecting the long-distance trade networks that brought borax from its sources in Central Asia to Mediterranean and European markets.

Modern chemistry recognizes borax as a hydrated sodium borate with distinctive properties: it forms a glassy bead when heated (the "borax bead test" used in analytical chemistry), it acts as a mild alkali in solution, and it forms complexes with various metal ions. The substance's practical applications in metallurgy and glassmaking were genuine chemical insights, even if the theoretical understanding was limited. Pamela Smith's research on artisanal knowledge has shown how craftsmen's expertise with substances like borax informed alchemical practice, creating a productive exchange between workshop techniques and laboratory experimentation. Borax thus represents the intersection of craft knowledge, commercial trade, and alchemical investigation, a substance whose practical utility made it valuable across multiple domains of early modern material culture.

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