Talk Report: 2016-10-12

Stained glass conservation by Steve Clare

Steve Clare set up Holywell Glass in Wells 20 years ago and he and his team were responsible for the amazingly impressive and complex restoration of the great Jesse Window in Wells Cathedral. On Wednesday October 12th Steve came to talk to us about his work, entitling the lecture ‘Stained Glass - Art, Craft and Conservation.’

The work done by the conservators at Holywell Glass covers a wide range of challenges: from medieval through to contemporary work in private collections, to churches and cathedrals all over the country. His team consists of twelve conservators, including two apprentices. They work with a mix of many skills with the challenge always to work in a manner that is both sensitive and authentic. As well as being artists and craftsmen, the conservators have to have a grasp of the science of glass and to understand the different materials that they will handle including adhesives, stone and lead.

We were told about the various ways that the lead-work is formed: in medieval times the strips were cast but they are now mostly milled. At one time it was thought that lead work in stained glass windows needed replacing every 50 years. Now we know that the lead strips can last for well over 100 years so that usually only minor repair work is necessary. The leading in the windows of Kings College chapel in Cambridge, has lasted very well for 140 years.

We were taken through the various ways that traditional stained glass is made by the, often German, manufacturer. It can be blown into flutes and spun into great flat discs, or blown into cylinders which are flattened into sheets of glass at high temperature or moulded into square wood forms. The resulting sheets of glass are then cut into flat pieces, for use by the conservators and we saw an image of the range of test pieces which are made to find the exact colours required. Surface decoration in the form of lines and texture painted on the glass has been used since mediaeval times. Ground glass with iron or copper oxide is mixed with water or vinegar (traditionally urine) and painted onto the glass in the style of the original piece that is being replaced and fired in a kiln at 660 degrees.

Steve showed us a photo of the head of the crucified Jesus in the Jesse Window. This head is the focal point of the whole window and a complete piece of glass was missing; for both theological and aesthetic reasons it was decided that this must be replaced. We saw where the missing cheek and eye were being painted in ground glass by a conservator: the replaced glass when finished blended perfectly with the mediaeval original. A very detailed plan is followed when working with these priceless windows and alterations such as this are carefully recorded for posterity. Details can also be added on an extra thin piece of glass, which is glued on the outside of the damaged glass.

Condensation on the old glass in cathedrals has caused great damage over the years. The amount of potash in early glass meant it was easily attacked and the acid in the lichens, which grow affects the surface. The coke used in the Gurney stoves found in almost all cathedrals in the late 19th and early 20th centuries “made the air reek with brimstone”! This made the glass dim and much colour was lost. With conservators’ knowledge and skills these damaged areas of glass are cleaned and, with new techniques are evolving all the time, pieces can be reclaimed, that in the past would have been considered beyond repair.

In addition, the weather attacks the glass from the outside. The modern approach is to protect restored windows by adding another layer of glass to protect the outside surface. At Wells this is carefully hinged so access to different areas of the window is easy. We were surprised to learn that the glass on the outside of the Jesse Window is divided with leads into a criss-cross diamond pattern. This successful idea was the contribution of Peter Bird, the cathedral architect at the time: it makes the glass much stronger and prevents it glittering disconcertingly when seen from afar in sun light.

Before work on a project like the Jesse Window can start many different bodies have to be involved. The clients (in this case the Church), the architects, experts in different disciplines and external advisory groups must all be consulted and checks have to be made constantly throughout the restoration. But it is Steve and his team who are the artists and craftsmen who do the work with such skill and patience. We should be proud that Holywell Glass, based in Wells, has restored the wonderful golden Jesse Window to its former glory and that they continue to do magnificent work all over the country. Steve was thanked enthusiastically for sparing the time to give members such a fascinating and informative talk.