The Conservation of Alabaster
|Detail of monument to Thomas Withering (1625) being cleaned in the studio of Taylor Pearce. Thomas Withering was Postmaster General to Charles I.|
Alabaster is a form of gypsum, hydrated calcium sulphate. Gypsum is used extensively in plaster and mortar and is added to Portland cement to inhibit the setting period. During quarrying or mining for this mineral, large compounded blocks would be encountered and these were alabaster. Unfortunately, according to the technical advisor to the Stone Federation Great Britain, John Bysouth, alabaster is no longer extracted in the UK, or if it is it isn’t appearing on any major radar screen. A British Gypsum spokesperson said that as far as their estates are concerned it simply doesn’t exist in large enough quantities to make its continued extraction economically viable. However, there is still a significant mined reserve of British alabaster left in the UK. It is owned by the Nigel Owen Organisation of Northampton. This company, which now quarries soap stone, finds itself the owner of a spectacular ‘bin-end’ of what is probably the last of the UK’s stock above ground. Nigel Owen himself must be the UK’s leading expert on this stone having been involved with alabaster since 1945. He reckons that at the present rate of take up (mostly to sculptors, who won’t thank me for divulging this information) there is a two year supply. It is available in workman-like blocks of around a foot square.
These sculptors who are buying from the Owen bin-end represent the last knocking, or more properly, tappings of a great British tradition that, according to most authorities, really took off in the late Middle Ages, just before the Black Death.
Far too soft for external use, Alabaster is hopelessly vulnerable to the elements, and it is too weak for building. It is so soft that it can be cut with a penknife, making it a ready target for vandals over the ages. The very ease with which it could be carved with finally wrought detail was one of the reasons for its popularity for tomb sculptures and other internal devotional features, like reredoses, triptychs and panels. The other reason, of course, was its spectacular appearance. All alabaster has a unique translucent quality that even the most desensitised individual should be able to distinguish from marble. The colour spectrum ranges from a creamy white (very rare) to a dark honey colour. Whatever the colour, it is made up of dozens of veins. In colour these may be anything from dozens of shades of white to veins of pink and reddish brown.
The discovery of large accessible and workable deposits of alabaster around Nottingham at the end of the 14th century arrived just in time to satisfy the aspirations of all the arrivistes who had prospered in the period that followed the Black Death. They wanted to both demonstrate their gentility in the here-and-now and guarantee their place in the hereafter via an ostentatious contribution to their local church. Easy to carve, easy to work, British alabaster was the ideal stone to cope with needs of the mass affluent. Production from Nottingham reached the sort of proportions that were not to be experienced again until the 18th century in the potteries. It didn’t just stay in England. English alabaster, from small votive statues to the Virgin to large funerary monuments and tombs, was exported from Nottingham all over European Christendom, from Iceland to Spain. It has to be said that the quality of much of this production was very poor, often knocked out in pattern book style, seemingly by the yard. Late Medieval and early modern alabaster does have its great moments, however, and most of it is still highly acceptable when compared to the great Victorian alabaster carving revival when, what Alec Clifton-Taylor memorably referred to as a ‘streaky bacon’ alabaster, stalked the land along with other strange Victorian ecclesiastical enthusiasms. Alabaster is not just confined to churches however, and its use in the so-called ‘Marble Hall’ of Holkham Hall, Norfolk is regarded by some authorities as the way that it should be used to create a spectacular, almost theatrical effect. However, most alabaster encountered by the restorer and conservator is located in churches, more often than not as part of a funerary monument.
CONSERVATION AND REPAIR
There are certain rules of engagement that apply to alabaster, as they do to any stone that is undergoing conservation. Firstly, whatever procedure is employed must, wherever possible, be reversible and secondly, the aim of the exercise is not costume drama, attempting to return the subject to its original form, but rather to stabilise the subject in the present. Fortunately that means the virtual disappearance of alabaster from the scene is not a problem from the conservator’s point of view. Missing heads and extremities do not need to be replaced - that is provided they were lost as the result of several hundred years of wear and tear or even removed by a vandal, if it was a good class of vandal and a long time ago, like one of Edward VI’s or Cromwell’s iconoclasts. However, the activities of modern vandals have to be expunged from the historic record.
All vandalism must be left to specialists to treat. Spray paint for example may be readily removed using acetone or dichloromethane, but tests may be necessary to establish which solvent is required, and skill is required to remove the pigment thoroughly.
Before any work can be undertaken it is absolutely necessary that a condition report and a specification of work be prepared. As often as not all the work required cannot be undertaken on site, and the subject, or portions of it, have to be dismantled and removed to the conservation studio or workshop. Anybody budgeting for an exercise of this kind should bear in mind that a dismantling process may also reveal other problems hitherto unsuspected, that may have to be tackled. Recently conservators from Taylor Pearce encountered a nest of wild bees in a tomb. Clearly aware of their protected status the bees refused all the blandishments of an apiarist to resettle them, and in the end the conservators managed, with the agreement of the client, to strike up a modus vivendi with them, managing to work around them.
Funerary monuments account for the bulk of alabaster encountered by the conservator. However, few of these consist entirely of this material. It is often used in combination with marbles and sandstones, for instance, which require similar but different conservation procedures.
The main problems that alabaster presents to the conservator spring from its softness and susceptibility to the elements, and one of the most common, caused by water penetration, is rusting ferrous fixings and cramps. Besides staining, corroding iron can cause the stone to fracture and ultimately render a complete monument unstable and dangerous. The treatment is to remove all ferrous fixings and replace them with stainless steel fixings and cramps set in resin adhesives. Sometimes the troublesome ferrous material was introduced in 19th century restorations, as the fixings of many monuments down to the 17th century were more usually non-ferrous. Sheep bones were a particularly popular alternative. Indeed probably one of the biggest problems facing the conservator of alabaster, or any other stone, is botched or failed restoration procedures carried out in the past. Even the first epoxy resin repairs are now starting to emerge as subjects for treatment.
Much can be done to correct poor restoration or repair. For instance old repair plaster can be removed from a feature and break joints filled with a matching aggregate combined with a resin fill such as Paraloid, touched in to match the adjacent surface.
The area where alabaster needs the greatest attention, and where the results of a job well done are particularly gratifying, is in the cleaning and finishing processes. It may seem unecessary to observe that this is not a job for amateurs, but there have been a number of well recorded atrocities carried out, particularly against alabaster funerary monuments, by well meaning incumbents and their flocks over the years.
Usually alabaster, however begrimed by the centuries, will clean up beautifully. One great virtue of this stone is that, unlike marble, it rarely stains and if it does, as often as not the stain can pass off as one of its veins. In fact the veins are a kind of staining.
It should be remembered that up until the beginning of the 17th century, alabaster monuments were usually painted in places. Therefore it is important to carry out a careful examination for traces of polychromy so that paint layers can be tested for stability and resistance to solvents prior to cleaning. Subsequently any flaking areas discovered during cleaning need to be consolidated with Paraloid resin.
Alabaster should be cleaned using mild solvents. The type and strength of solvents has to be determined by on-site tests but the most usual is a mix containing white spirit, de-ionised water and a small quantity of non-ionic detergent. The actual cleaning is carried out using cotton wool swabs dampened by the solvent. After cleaning the subject should be protected by the application of a cosmolloid wax. This will restore the magic quality to this most agreeable of stones.