Travelling altar: Investigating an object

The travelling altar, museum number M.54-1930,was acquired by the Victoria and Albert Museum in 1930 for the sum of £1500. It was made in 1574 for the Delgado family in Milan and would have formed part of the fittings of a nobleman’s private chapel. At this time a wealthy man with large estates would have spent a lot of time moving from one house to another and this altar would have travelled with him. The altar has its own case painted with the arms of the family, and it is lined inside with red velvet embroidered with gold and silver thread. It is currently being treated for display as part of the redevelopment of the Silver Galleries, due to open in November 2002.

 The altar itself is made of steel damascened or inlaid with gold and silver, the bare steel then blackened to provide contrast. The steel provides a framework for the display of four verre eglomisé panels depicting the life of Christ. Verre eglomisé is a decorative technique where a thin sheet of gold is applied to the back of a glass panel with isinglass. A design is scratched through the gold, other areas are scraped away and colours are then applied in a transparent oil medium. The whole is backed with silver foil to add lustre. The panels of our altar are also backed with lead foil for extra protection.

Prior to any work being carried out the altar was photographed by the Museum photographic section in addition to the record shots taken by the Conservation Section. It was also examined by x-radiography to see if its construction could be more easily understood. The images revealed that the altar was made of several small panels held together with mortice and tenon joints.

Figure 1. Travelling altar before conservation, Museum No M.54-1930 (click image for larger version)

The altar had previously been examined in 1977, when the condition of the verre eglomisé panels had been of concern. They were deemed ‘untreatable’ at that time, and re-examination during the current treatment proved that diagnosis to be correct for the following reasons. The lead foil on the back of the paintings is firmly adhered to the paint layer, the paint has also become detached in places from the glass leading to an opaque look in areas. Removal of the lead foil and attempting to re-adhere the paint layer would probably do more harm than good, as the paint layer would probably come away with the foil. The best course of action is to leave well alone, in the hope that, in the future, a treatment may be developed to re-adhere the paint layer.

The 1977 conservation report makes no mention of the condition of the metalwork, or any treatment carried out on it. Traditionally, the final surface finish for armour and damascened ware was a coat of oil applied with bread. Subsequent cleaning was also carried out by rubbing with bread. Although this may appear odd it would be quite effective, as the slightly sticky bread would remove dust and being soft there would be no danger of scratching the decorated surface. Any crumbs left behind could be brushed off. Examination of the metal surfaces under a low magnification stereo microscope showed that the surface was covered with a brown tar-like coating. A sample analysed by the V&A’s Science Section revealed the presence of shellac. Shellac is a secretion from scale insects (Laccifer Lacca) cultivated mostly in India and Thailand. The secretion is produced primarily as a protective coating against predators and it takes approximately 300,000 insects to produce 1 kilo of shellac.

The presence of shellac in the brown coating would not be consistent with the original oil protection, since shellac itself is not mentioned in western literature until the late 16th century (when it was used for its colouring properties) at least 20 years after the altar was made. It was not used as a liquid protective coating (it was dissolved in alcohol), until the end of the 18th century.

It is reasonable therefore to assume that the brown shellac containing coating was applied well after the altar was made and before the altar was acquired by the museum, sometime in the 19th century.We do not know the precise makeup of the coating but an example of a typical 19th century lacquer recipe is shown in the box.

Figure 2. Detail of the altar, before conservation. Photography by Donna Stevens (click image for larger version)

Plain Lacquer Varnish

4oz sandrach, 12oz button shellac, 2 quarts alcohol (methylated spirits) Churn for twelve hours, then strain and settle. Decant the clear liquid into jars and cork or secure them soundly. Spon’s Workshop Recipes for Manufacturers and Scientific Amateurs, vol. III page 35, Pub E & F N Spon, London 1909.

A coat of shellac would have brightened the look of the altar and, as it dulled down over the years, it could have been ‘revived’ by another coat of shellac. This scenario would explain the quite thick layer of coating which was found in some of the crevices on the object.

As the coating was not original and was obscuring surface detail it was removed. This was completed in small areas under magnification using small swabs of Industrial Methylated Spirit (IMS) and acetone, taking great care that the solvent did not go near the remaining verre eglomisé panel which could not be removed. Removal of the coating revealed the presence of extensive silver inlay. This silver which had tarnished black and been hidden under the shellac is not mentioned in the 1930 original acquisition description in the museum files. This is another indication that the coating was applied and had darkened prior to the object being acquired by the V&A.

Figure 3. Detail of the altar, after conservation, showing silver inlay. Photography by Donna Stevens (click image for larger version)

Removing the obscuring coating revealed the manufacturing process more clearly. The object was decorated with gold and silver patterns and figures, a process known as damascening. There are two main methods of achieving this effect. One called inlay, is to cut the pattern into the iron or steel surface, and then to push gold or silver wires or pieces of sheet into the cuts. The cuts were made at an angle to the surface, to create an undercut, so that the sheet or wire, once pushed in, would be held in place. The other method, used on the altar, is called overlay. Here, the iron or steel surface is first hatched with criss-cross lines and the gold or silver is then hammered onto the surface. The hatched lines provide a key to hold the precious metal in place; no solder or adhesive is used. The gold used in the case of the altar was a wire made of two strands twined around each other.

Unfortunately it was not possible to get to the back of the repousséed sections. However some copper corrosion products in the crevices indicates the presence of copper alloy solder compounds. These may show that the iron was not repousséed from several large sheets but may have been assembled from smaller sections joined together.

After treatment the metal was waxed with ‘Renaissance’ microcrystalline wax. However, as the work took several weeks, it was noted that the newly revealed silver areas treated first were beginning to tarnish again, so it was decided to lacquer the silver areas only using ‘Frigilene’ cellulose nitrate lacquer to provide a more protective coating.

At the time of writing, the object is still undergoing conservation treatment. It is hoped that future advances in conservation techniques will enable the verre eglomisé panels to be restored to their former appearance.

I am grateful to Raymond White of the National Gallery for information on shellac, and to Ceramics Conservation at the V&A for the re-examination of the glass panels.