Museum tries to stem disease affecting glass: Chemists are being used to combat a disease that is shattering exhibits. Steve Connor reports

HUNDREDS of precious goblets and vases in the glass collection at the Victoria and Albert Museum are showing signs of an irreversible 'sickness' that ends with the objects collapsing under their own weight.

The glass disease is known as 'crizzling' and begins with the surface of the objects appearing to weep droplets of water or small deposits of salt. Eventually, cobwebs of tiny fractures develop and weaken the glass until it begins to flake. Most glass consists of silica mixed with alkaline compounds. It is the amount and proportion of these alkalis that determine the susceptibility of the glass to crizzling. As the alkalis react with water vapour, the outer surface of the glass begins to shrink, to produce eventually the cobwebs of fractures.

Conservationists have completed a survey of the ceramic collection that shows the problem is worse than curators had expected. They have called in chemists from Imperial College to help stem the crizzling process.

Four years ago, a preliminary survey showed that about 400 of the museum's 7,000 glass objects were affected by crizzling. A more detailed survey this year revealed that 821 objects showed weeping and salt deposition, and 25 were severely crizzled.

Vicky Oakley, a researcher in the museum's conservation department, said: 'It's quite alarming that it is such a high proportion.' The museum is trying to raise pounds 1m to build a new exhibition hall to house its glass collection in environmentally-controlled display cabinets that should stem the deterioration.

'There are pieces in the collection that have got to the point that there is nothing that can be done. When they are in that condition you can't even stick them back together,' Ms Oakley said. At least two items are believed to have collapsed from crizzling.

'Obviously it is worrying that some have reached a stage where they are beyond hope. That's why we're anxious to do something to stem the problem,' she said.

Glass sickness has affected a variety of exhibits from different eras - it can take decades or centuries for an object to disintegrate.

Among the affected exhibits at the V & A are 16th and 17th-century Venetian and Spanish vases and goblets. But crizzling has also taken its toll on 20th-century pieces of Scandinavian and Italian glass.

Oliver Watson, the curator of ceramics, said: 'We are more aware of this problem than many museums. Our collection is particularly rich in those pieces of glass where there is a risk of crizzling.' Until recently it was thought that the problem was restricted to a narrow range of objects, 'but the survey has made it quite clear that we are dealing with a large number of objects that are spread throughout the collection'.

Philip Rogers, a chemist at London University's Imperial College, said that the effects of crizzling depended on the composition of the glass. It could be slowed by carefully controlling the humidity of the air around the affected objects.

'Crizzling occurs as a result of the glass reacting with water vapour in the air,' he said. Using X-rays and electron microscopy, he analysed the chemical changes that took place in a crizzled Venetian glass goblet to understand the process better.

'It is a progressive problem and once it starts it is difficult to see how to reverse it,' Dr Rogers said.

Although polishing the glass with a hot flame, or covering the surface with a plastic film and putting the object in a dry environment, would stop crizzling, such severe treatment could not be contemplated by the museum because it would irreversibly alter the object. If susceptible glass had been exposed to water vapour, then putting it in a dry atmosphere would make it worse because the surface would shrink faster, Dr Rogers said.

Conservationists at the Victoria and Albert Museum agree that the best treatment for arresting the sickness seems to be to put the glass in a display case where the humidity and temperature are then both carefully controlled.

(Photographs omitted)