By Cathy Silverman

Before treatment

After treatment

When given a new project, I generally begin by consulting books, articles and treatment reports describing the conservation of similar objects or materials. So when I was allocated a shagreen-handled walking stick, I headed to the library to find out how to conserve this peculiar and, for me, previously un-encountered skin. I quickly discovered there was a real paucity of published information on this topic. This blog post describes the process of experimentation undertaken in order to devise an acceptable method of treatment.

But let us take a couple of steps backward: where did the walking stick come from, and what is shagreen?

The term shagreen is used to describe several distinct materials: donkey hide embossed with seeds, shark skin and ray skin. The walking stick is made of ray skin. This has been used across the centuries on a wide range of objects, from samurai sword hilts to Art Deco furniture. For more information about the material and its history, take a look at Abigail's 2012 post.

The walking stick once belonged to Francis Cadell (1883-1937), a Scottish Colourist painter renowned for his depictions of elegant interiors of his native Edinburgh. It is now owned by one of his descendants. When it arrived at West Dean College it was in a sad state-the top section of the handle had been separated from the rest of the stick, and the intervening 4 cm long section was missing. A previous student had already recreated the missing section from limewood, securing it to the original part of the stick internally, using carbon fibre rods. In addition to the new section, which had no shagreen covering, there were several areas where the scales were missing.

The owner wanted damaged areas to be restored, but was keen to preserve the object's patina and integrity. For my part, I wanted to ensure that the treatment adhered, as far as possible given the brief, to the ethical principles of conservation, upholding the key tenet of reversibility/retreatability.

I began to think about how to replace the individual missing scales. Scales were missing along the top of the cane (an area perhaps particularly vulnerable, due to handling) and along the joints, where the maker had evidently inserted scales in an effort to distract the eye from what would otherwise have been very straight lines.

Initially it was thought that these could be replaced using genuine shagreen scales, cut from the skin and glued in place. I experimented, removing scales from a scrap piece of shagreen using a scalpel, and gluing other scales in their place. This method was relatively straightforward and visually effective. Unfortunately, the shagreen available had scales that were significantly smaller than those needed for the object.

Scale shapes hand-modelled in Milliput epoxy putty and glued to MDF.

An impression was taken of the "scales" using Lab-Sil silicone putty to make a mould.

I therefore decided to make artificial scales from coloured resin. A mould was created by hand-modelling scale shapes from Milliput (a plasticine-like epoxy putty that hardens at room temperature). An impression was then taken using Lab-Sil (a kneadable silicone putty made for the dental industry).

Three resins were tested to see which would be the most suitable to use for the artificial scales —HXTAL NY-1 epoxy resin, West System 105 epoxy resin and Taranti GP polyester resin (left to right).

Three different resins were tested: two epoxy resins and one polyester resin. HXTAL NYL-1 epoxy resin was selected. Although it has a very long cure time (approximately 30 hours required for the small scales) and is expensive, the very small quantities needed meant the cost was justifiable. Its main advantages are that it is colourless and non-yellowing (unlike most other epoxy resins), compatible with the dyes available at college, and relatively non-toxic (especially compared to the polyester resin).

Orasol dyes, a range of colours with good light-fastness, were used to colour the resin. Initially dry powder dyes were added directly to the resin, however used in this way, the dyes only partially dissolved. Dyes were therefore mixed in acetone first. Experimentation demonstrated that it was necessary to make a fairly concentrated dye/acetone mix, so that the smallest amount of acetone could be added to the resin, otherwise shrinkage resulted from the evaporation of the solvent.

Left: Orasol dyes added directly to HXTAL NYL-1. Right: Orasol dyes premixed in acetone before being added to HXTAL NYL-1.

Fillers were also added to the resin in order to match the translucency of the original shagreen. Finely ground pumice powder, colloidal silica, whiting and glass microballoons were all tested. The colloidal silica gave the best effect, with the whiting tending to create a less even, grainy mixture with the resin, and the microballoons collecting in the centre of the "scale."

Left: HXTAL NYL-1 with microballoons.
Right: HXTAL NYL-1 with (left to right) colloidal silica, pumice powder, colloidal silica (larger proportion), microballoons, whiting.

In order to create a paler background and to allow the artificial scales to sit flush with the surface, the void was lined with Japanese tissue paper. The colour of the scale was then adjusted to the better match the surrounding scales both by painting the back of the scale and the Japanese tissue paper with watercolours and acrylics, before being glued in place using a spot of superglue. Although irreversible, the glue was being applied to the tissue paper, which, if necessary could be mechanically removed in the future. The artificial scale was then sanded and polished in situ to ensure it was flush with and of a similar sheen to surrounding scales. A stopping wax mixed to match the fill between the scales was rubbed into the area surrounding the scale.

Before voids were filled with artificial resin scales.

After adding scales

It would have been impractically time consuming to make individual scales to fill larger areas of loss in the shagreen. A technique commonly used for the conservation of leather was therefore employed. Layers of Japanese tissue coloured with Selladerm dyes were built up using poly(vinyl acetate) emulsion. By tearing the tissue instead of cutting, a very soft and unobtrusive edge can be created. The paper also creates a slightly mottled, translucent effect, which blends better than other fill materials. Watercolours were used to paint small circles and add further variation in colour to replicate the pattern of surrounding scales.

For the new section of handle, a real piece of shagreen was sourced. The trade in exotic skins is governed by The Convention of International Trade in Endangered Species. Shagreen falls into Appendix II which covers "species not necessarily threatened with extinction, but in which trade must be controlled". According to the regulations, skins must be imported into the EU accompanied by the export certificate issued by the government of the country of origin. It is therefore legal and relatively easy to source shagreen-it can even be bought from Ebay.

CAVEAT: Although it can be bought legally, there are ethical implications. There is an assumption that because rays are farmed as a food source in South East Asia, the fish are not being plundered from the wild, and their skins are a sustainable by-product. However, farming does not always relieve pressure on wild populations. Further, a recent report from the International Union for Conservation of Nature suggests that a quarter of chondrichthyans (including sharks and rays) are actually threatened with extinction.

Once a skin had been procured, a piece of shagreen was carefully selected in order to match the original shagreen as closely as possible. Rayskin has its largest placoid scales down the middle of the back, with the other scales gradually diminishing in size towards the edges. The maker has utilised this feature for decorative effect, with the largest scales running along the top edge of the handle. The surprisingly tough scales were ground down using a random orbital sander. Even with the coarsest paper available it took around 20 minutes to abrade a piece measuring just 12cm by 12cm. Selladerm leather dyes were used to colour the shagreen.

Shagreen handle with new piece of shagreen glued into position—before second stage of colouring and filling joint lines.

The shagreen piece was then cut approximately to size using a scalpel. In order for the shagreen to wrap smoothly round the compound curve of the new section it was necessary to dampen the piece of skin. Water was applied to the underside using a paintbrush, and blotted dry using kitchen roll. The shagreen expands and stretches significantly when wet, so it was important the shagreen was securely bonded whilst under tension, before it shrank back to its dry dimension. A fast-acting glue that would cure in the presence of considerable moisture was therefore required. Superglue was found to be very effective. Although irreversible, this is ethically justifiable, as the glue will only be applied to the new spliced in section, rather than to the original object. The shagreen piece was then filed and sanded so that it better followed the contour of the rest of the shagreen handle.

The dye had achieved a quite consistent colour across the new piece, which was very noticeable when compared to the surrounding shagreen which exhibited much greater variation in colour. A range of watercolours and acrylics were used to match the variation.

More detail and colour was added using watercolours, acrylics and dyes.

Although a reasonably tight join had been achieved, the joint lines disrupted the pattern of scales and were distracting to the eye. Japanese tissue paper was once again used to disguise the cracks. The gaps between the scales were again filled with a coloured wax.

The colour and wax used on the handle were sealed in with layers of Paraloid B-72 in xylene (5% w/v) and the the whole thing was given a light coating of microcrystalline wax.

All in all this was a challenging and valuable learning experience. Including all the testing, the treatment took an extremely long time, but I am pleased with the outcome.

There are some considerations that may be worth noting if you ever find yourself conserving a shagreen object. Firstly, the use of superglue, whilst acceptable in this situation, would be difficult to justify if one needed to glue the shagreen to a substrate that was an original part of the object. Secondly, a lot of the colour, particularly on the new piece of shagreen, is only surface-deep. If the walking stick were intended for use, it would inevitably wear off with time.