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The art of producing appealing alloys is as rich as the evolution of metals.

Byline: JEFFERY MUSE

BRASS can alter in colour depending on how much zinc and copper is used in its manufacture.

If up to 8pc is zinc, the alloy produces a copper colour while between 8pc and 14pc it becomes a reddishgold, known as "Tombac" or "red brass".

A purer golden colour is obtained between 14pc and 17pc and a pale gold colour is achieved between 17pc and 30pc.

But between 30pc and 40pc of zinc the Victorian metal known as pinchbeck is produced, which was greatly favoured by many Victorians who wanted watches and jewellery that looked as much like gold as possible.

Christopher Pinchbeck (16701832) was a famous London watch and clock maker who invented an alloy of five parts copper to one part zinc, which looked extremely like gold. For jewellery and watches the proportions were more likely to be 4 parts copper and 3 of zinc, as this was more likely to produce a better colour to the finished piece.

Between 40pc and 53pc of zinc, produces a reddish-white tone in the alloy, and from 53pc to 56pc a more yellowish white pigment emerges.

However from 56pc to 67pc the alloy shows a definite blue white colour. And adding just another 3pc of zinc makes a lead coloured brass, thereafter, to 80pc the zinc dominates and produces its own distinct colour.

As zinc varies in quality the eventual colour in the final metal will depend upon the original ore's purity, which must have proved extremely irksome to William Champion who discovered how to distil pure zinc from the ore in the late 1730s.

The difficulty lay in securing a satisfactory mix of zinc and copper because the former melts more easily.

In 1781, however, James Emerson discovered how to make brass by direct fusion, whereby he introduced pure metallic zinc into molten copper, but the zinc was still difficult to handle at the temperatures needed to succeed. Increasing the amount of zinc had many drawbacks, not least of which was that the resulting alloy was very brittle and unappealing.

To mix 16 parts copper and 41/2 parts zinc makes Bath Metal, which is also known as Prince's Metal or Rupert's Metal. The mix of six parts copper and two parts zinc has a wonderful golden hue, which was invented by Prince Rupert in the 1670s, cousin of Charles II and Governor of the United Societies.

The mixture was heated until red and then immersed in a solution of diluted spirit of vitriol, or sulphuric acid, to eradicate any impurities from the surface, which could then be polished to a good shine.

After the cleansing dip it was necessary to scrape or wash the dirt off before a quick plunge in aqua fortis, then buffed with an agate or bloodstone. The resulting alloy was mainly used for button making, which is why so many old buttons easily tarnish.

Brass was manufactured by the cementation method until the end of the 18th Century, whereby the molten mix was heated in a crucible until the quantity of natural carbonate of zinc, or lapis calaminaris, copper and charcoal had fused.

The quantities were about 3:3:2 and although the results varied greatly, this is still a very popular alloy and widely used today.

It followed on from bronze, thought to be the first alloy made by man, being an alloy of copper and tin and like brass more red than yellow.

In a ratio of 9:1 the alloy is friable but cannot be worked in sheet and is only suitable for casting purposes.

Bronze remains the popular choice for sculptors, being robust, heavy and relative inexpensive.

Adrien Etienne Gaudez (18451902) studied at the Ecole des Beaux Arts in Paris, where he began at the Salon in 1870. A popular opera at the time was Mignon by Ambroise Thomas, in which a young girl is snatched from her parents as a child.

This prompted innumerable figures of young maidens being created for the French market by artists and sculptors, in a variety of forms.

Contact Jeffery Muse at Phillips in Wales. Tel: 029 2072 7980.
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Title Annotation:Features
Publication:Western Mail (Cardiff, Wales)
Date:Oct 20, 2001
Words:686
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