Future look at history

Press, 20 December 1985, Page 18

Future look at history

By

PAUL LASHMAR,

of the

London ‘Observer’

A space-age weapon has joined the ranks at Britain’s National Museum of Arms and Armour, better known as the Royal Armouries, to assist the curators’ battle to conserve the 35,000 antique swords, guns, and pieces of armour in the collection.

The Kevex 0750 A macroanalyser looks as if it would be more at home in President Reagan’s “Star Wars” programme than in the medieval surrounds of the Tower of London.

The macroanalyser uses an Xray beam to identify exactly what and how much of each metal is in an object without — most importantly — causing it any damage. Bob Smith, the Royal Armouries chief conservator, says: “It can be used for spotting forgeries and, to some extent, for dating. But its greatest strength is identifying what a sword, for example, is made of, so we know how exactly

to conserve it.” It has already been used on the Royal Armouries’ prize exhibits, four suits of armour which belonged to Henry VIII. The Kevex macroanalyser at the Royal Armouries is the first in use in Britain. It employs a process called X-ray fluorescence, by which a small area of an object’s surface is bombarded with X-rays. This deflects electrons which are then detected and measured. As different elements give off different energy patterns, the results are analysed in a computer and the quantities of each element present are shown.

Macroanalysers were developed for industrial use where they carry out quality checks on, say, turbine

blades, without needing to isolate a sample of metal for testing. It was this non-destructive method of testing that first made the machine popular in the United States among conservators, art historians, and archaeologists, so Kevex, a Californian company, built this model specifically for museum use. It is precisely because of these non-destructive qualities that X-ray fluorescence was used to show that there are traces of blood on the Shroud of Turin. The New York Metropolitan Museum of Art recently used the Kevex machine to identify what pigments had been used by the artist Rembrandt to achieve certain grey tones in a series of his drawings. The answer enabled the museum to conserve the drawings correctly. During the tests, the machine showed its versatility by also indicating that one drawing had been previously restored this century, by identifying traces of titanium dioxide, a constituent of white paint used only since 1910. The Royal Armouries bought their machine six months ago for $210,000 and have now installed it in a small room in a thirteenthcentury tower. It is freestanding and can be used on an object of any size. Bob Smith says the machine has some limitations. The X-rays only penetrate to the minute depth of 500 microns, so only surface elements can be identified. For instance, if a surface has been gilded, it is not possibe to find out what is underneath unless there is wear or corrosion. It is not much good, either, for identifying elements with atomic weights of less than 15: it cannot easily detect carbon and is most useful for metal analysis.

His first major project is to analyse samples of brass on dated objects over a long period. Old brass tends to be very impure and its components vary greatly according to date and the place of manufacture. He intends to obtain a wide range of samples so that the macroanalyser can help to put a date to brass weapons in the same way tree rings are used to date wood; that is, by comparing

the tree rings of known date with . ” the tree rings of the wood of unknown date. j* The most interesting use to ' which the macroanalyser has been r;’’ put so far is to help solve the '£ controversy over whether Victoria Crosses were cast from cannons captured from the Russians during the Crimean War.

By comparing a selection of a ■ dozen or so V.C.s from different periods, they have come up with *• some intersting new clues. Bob Smith has found that the earlier V. C.s up to the First World War, f were made from bronze from one J gun with, unusually, a small quantity of platinum. They have not yet identified which gun this metal ’>* came from.

However, all V.C.S from the First World War seem to have * been made from bronze taken from two Chinese guns of the seven- . , teenth/eighteenth century which now stand outside the Royal Arse- £ nal. While this points against the original legend, Mr Smith says: “It “ is just possible that the Russians, tJ who regularly fought on the south- ■" ern and eastern ends of their £ country, might have been using f captured Chinese guns at Sebasto- ? pol.” He hopes that the macroanaiyser will eventually clear the matter up once and for all.

The Royal Armouries intend-to make the macroanalyser available f • to other museums and members of the public early next year — the ’• first service of its kind to be .; offered in Britain. ~ “We had a woman in here who “ asked us to tell her whether a pair of medieval spurs were, as the popular family story had it, made of silver. In fact they were covered in lead tin alloy. When we checked we found all our medieval spurs >* were covered in lead tin alloy to •*" stop corrosion," says Mr Smith, y“We will offer the service for F, around $BO an hour, which will £ effectively be the cost of the most , basic check just to establish what.«» something is made of.” Only three other museums in Britain have X-ray fluorescence «> machines. The British Museum and the Scottish Museum in Edinburgh ~ have machines which are virtually home made. The Victoria and Albert Museum £ have had a machine built by the . European subsidiary of a United States company, Tracor. t