Tombac


Tombac, or tombak, is a brass alloy with high copper content and 5–20% zinc content. Tin, lead or arsenic may be added for colouration.
It is a cheap malleable alloy mainly used for medals, ornament, decoration and some munitions.
In older use, the term may apply to brass alloy with a zinc content as high as 28–35%.

Etymology

The term tombak is derived from tembaga, an Indonesian/Malay word of Javanese origin meaning 'copper'. Tembaga entered Dutch usage concurrent with their colonisation of Indonesia. Likely, the term was used generically to describe Indonesian high-copper brass items, including gamelan gongs. It is one of the very few Indonesian loan words used in English or German.

Common types

  • Modern CuZn15 – tombak with a gold colour, very good for cold forming, suitable for pressing, hammering, or embossing
  • modern CuZn12 – same characteristics and applications as CuZn15, slightly different colour
  • modern CuZn10 – similar characteristics and applications as CuZn15 and CuZn12, noticeable reddish colour
  • modern white tombac – CuZn10 that is zinc content 10%, with trace arsenic
  • modern enamel tombac or emailler tombak – an alloy of 95% copper and 5% zinc, suitable for enamelling, therefore the name.
Ure notes the following forms of tombak in widespread use during the time the text was published :
  • "Gilting tombac":
  • *Copper 82%, zinc 18%, lead 1.5%, tin 3%
  • *Copper 82%, zinc 18%, lead 3%, tin 1%
  • *Copper 82%, zinc 18%, lead, tin 0.2%
  • "French tombac for sword handles", pommels and fittings: copper 80%, zinc 17%, 3% tin
  • "Yellow tombac of Paris" for gilt ornaments: copper 85%, zinc 15%, trace% tin
  • "Hanover tombac": copper 85.3%, zinc 14.7%
  • Chrysochalk: copper 86%, zinc 14%
  • Alkeizatlee: copper 66.4%, zinc 16.6%, lead 5.7%, tin 10%, magnesium 1.3%
  • "Red tombac of Paris": copper 90%, zinc 7.9%, 1.5% lead
  • "Red tombac of Vienna": copper 97.8%, zinc 2.2%
Piggot states the brass used for machinery and locomotives in England was composed of copper 74.5%, zinc 25%, and lead 0.5%, which would make it a tombac according to Ure.
Piggot's own definition of tombak is problematic at best: "red brass, or tombak, as it is called by some, has a great preponderance of copper, from 5 ounces of zinc down to 1/4 ounce of zinc to the pound ."

Tempers

Typical tempers are soft annealed and rolled hard.

Applications

Tombac is soft and easy to work by hand: hand tools can easily punch, cut, enamel, repousse, engrave, gild, or etch it. It has a higher sheen than most brasses or copper, and does not easily tarnish.
Historically, it was used by the Javanese as a faux gold finish for objects d'art and ornaments.