Questions to a metals conservator
Read more about the metals conservation department on this website.
What's the oldest thing you have worked on?
I have worked on a copper alloy sheet with carbonised textile adhering to it, from Ur in Mesopotamia from approximately 2,600BC.
What's the biggest thing you have worked on?
I worked on the Statue of Quan Yin on display in the World Cultures gallery at World Museum.
What is your favourite object of those you have worked on?
The pair of ‘flageolots’ in the World Cultures Gallery in World Museum. I like them so much because they were made in the Potala Palace workshops in Lhasa for the 13th Dhalai Lhama.
Tibetan flageolot and a Spanish or Portuguese pendant brooch of the early 17th century
Also,a pendant brooch made of gold with rose quartz and garnets in cabochon settings and enamel inlays. The enamels are very delicately applied with a wide range of colours. There is a turquoise green, an emerald green and a pale blue whilst the white has been enhanced with fine lines of pink and black. The black on the outer rim has largely been lost but the remaining inner ring shows how it would have looked. Much of the detail can only be seen with very close inspection and some of it is not seen at all unless the object is dismantled.
Bronze sculpture of the Buddha of compassion, currently on display in the World Cultures gallery
How do I know if my sculpture is made of brass or bronze?
Brass and bronze are both alloys of copper. Bronze was first produced in antiquity and the rich brown patination it develops has therefore always been associated with classical statuary. This has continued through to today. Brass has only been mass-produced since the late 18th century, but it is a much cheaper material than bronze, so most cast objects produced since 1800 have been brass. Brass can be patinated in very similar browns as bronze. Because there was a desire for 'bronze' sculpture, many small domestic sculptural pieces cast in the 19th century were made in a cheaper 'white' metal (eg lead, tin or zinc based alloys) and coloured with pigments to appear the same as a bronze piece.
The alloy in brass is zinc and in bronze is tin, with a range of percentage present being possible. The bare metal of both bronze and brass have a golden yellow colour which can be darker, lighter or pinker with the varying amounts of the alloying metal present. This makes categorically identifying one from the other just on a visual basis very difficult. An educated guess can be made based on the age of an object, its place of origin, the maker (if known), and the hue of the metal. Brass is usually a brighter yellow than bronze and bronze is usually pinker then brass. To be categorically sure, a sample would need to be analysed in the SEM/EDX, which would reveal the presence of either zinc or tin. Very few of the objects in the collections have been analysed in this way and their classification is based on the information as we have outlined above.
The Benin Bronzes are given that name as a group, though few of them are necessarily bronze. Only some of the Benin Bronzes in the collection have been analysed which showed they had varying amounts of the alloying metals present and whilst some had tin most had zinc. It is thought that the Benin metal smiths were re-using other brass objects, possibly from a European source, as material to re-use in their castings.