Gold leather wall hangings were highly coveted and extremely valuable among princesses and princes in the 18th century. Only a few of these luxurious Baroque wall hangings have survived to this day. It is therefore all the more remarkable that one has survived at the World Heritage Site of Augustusburg Palace and Falkenlust Palace in Brühl – in the Knights’ Parlor at Augustusburg Palace. RESTAURO visited the two restorers Kristin Krupa and Inken Süß in their workshop. […]

In the 18th century, gold leather wall hangings were highly coveted and extremely valuable among princesses and princes. Only a few of these luxurious Baroque wall hangings have survived to this day. It is therefore all the more remarkable that one has survived at the World Heritage Site of Augustusburg Palace and Falkenlust Palace in Brühl – in the Knights’ Parlor at Augustusburg Palace. RESTAURO visited the two restorers Kristin Krupa and Inken Süß in their workshop.

The “Corduan leather” or “Peau d’Espagne”, as the gold leather wallpaper was also called, which emerged in the 16th century, goes back to the Moors in Cordoba, Andalusia. It was they who brought the technique of making gold leather to Spain, from where it spread across Europe. It found its way into the royal palaces of the Baroque period, as gold leather wallpaper had the advantage over the widespread tapestries that it was more resistant to moisture. And vermin also attacked woven tapestries much more frequently than gold-leather wallpaper. The production of peau d’Espagne was costly, time-consuming and laborious, which also explains why only the nobility could afford such a luxury item. Auguste Denis Fougeroux de Bondaroy described the process of making gold leather wallpaper in 1763. The skin of sheep, goats and calves was used, which had to be young and healthy. The rough steps of the production process were as follows: First, the hide was cleaned and tanned, then workers cut it into rectangles. In the next step, parchment glue was applied to fix wafer-thin sheets of silver leaf, which were later polished. This was followed by a further application of parchment glue or egg white – at least according to various sources. However, this step can only be verified for very few objects. In the next step, the leather was coated with gold lacquer. The leather was then punched or embossed with a model. There are leather tapestries that were only embossed or punched, but there are also cases where both embossing and punching were used. In the case of the gold leather wallpaper in Augustusburg Castle, it is possible to speak of embossing. Opaque or translucent colors were applied as a final touch. After these elaborate processes, the gold-leather wallpaper squares were ready to be sewn or glued together. If they were glued together, they were overlapped; if they were sewn together, this was done by folding the seam edges back. The gold-leather wallpapers were probably not permanently attached to the walls. There were various ways of attaching them, for example, some wallpapers had loops sewn to the top edges on which they were hung so that they hung down. Another option was to attach them to wooden strips using nails. The first type of attachment was naturally more temporary than the second. With both types, however, it was possible to change the gold leather wallpaper according to the season or fashion.

The Cologne Elector and Archbishop Clemens August (1700-1761) had a summer residence planned in Brühl from 1725. After he had the architect Johann Conrad Schlaun replaced by François de Cuvilliés, the extensive work began in 1728. Clemens August had exquisite taste and spared neither expense nor effort in decorating his palace buildings. He engaged renowned artists such as Carlo Carlone and the architect Balthasar Neumann. Clemens August chose a valuable gold leather wallpaper for the so-called Knight’s Room at Augustusburg Palace. The room was used from 1730 and served as the entrance to the so-called Winter Apartment. It is disputed whether the gold leather wallpaper in the room today is the original wall covering. However, research clearly shows that the Brühl gold-leather wall covering consists of two wallpapers with different motifs. While all the field squares show the same motif, the upper, final frieze consists of panels of another motif cut in two. However, the motifs can be dated to roughly the same period. The 18th century inventories report a leather wallpaper, a billiard table and three supraport paintings depicting hunting and armistice scenes. In the 19th century, these three paintings above the doors were replaced by depictions of children from a Wittelsbach collateral line.

The gold leather wallpaper was treated back in the 1950s, but according to current knowledge, this must be classified as improper. The restorers Kristin Krupa and Inken Süß have been entrusted with the task of reversing these measures since 2003. The craftsmen entrusted with the work in the 1950s had backed the wallpaper with mattress fabric, which they glued to the reverse sides. The individual squares were also firmly sewn together. The disadvantage of this approach is that the leather reacts to fluctuations in temperature and humidity, but this was no longer possible due to the rigid bonding with the fabric and the fixed seams. It could no longer expand or contract, which resulted in considerable damage. In addition, the restorers of the 1950s carried out retouching, which was not only limited to the damaged areas, but also extended to the often still well-preserved gold lacquer application.
The two restorers are working wall by wall and began with the south wall in 2003. The first step is to remove the gold-leather wallpaper from the wall and divide it into segments for transportation. The most practical solution turned out to be to work on two strips. As soon as the wallpaper is in the workshop, Krupa and Süß document the front and back using photography, and the seams, damage and changes are mapped. In addition, each panel is numbered and the wall on which the piece was located is also noted. This ensures that the gold leather wallpaper is sewn back in the correct order and returned to its original position on the wall. The restorers then carefully undo the seams that were sewn through the mattress fabric by the craftsmen in the 1950s. The aim is to preserve the original seams as much as possible.

It took several attempts before they found the best method for removing the mattress fabric. The problem is that the front side, especially the gold lacquer, is very sensitive to solvents. Only non-polar solvents can be used, but these do not dissolve the PVA in the adhesive. Kristin Krupa and Inken Süß therefore decided to modify the water and make the reaction time more controllable by thickening it. The restorers opted for an aqueous gel based on Tylose. The gel also had to be solvent-free to prevent damage to the gold leather wallpaper. The gel offers the advantage of being able to control how much moisture is absorbed into the structure, as leather is extremely sensitive to moisture. In addition, the relatively viscous gel is heated, but great care is taken to ensure that not too much heat is generated, as this would damage the leather. Leather has a shrinkage temperature and would contract if too much heat is combined with moisture, which would be irreversible. After applying the gel, the treated area is covered with a film to allow the gel to take effect. This treatment causes the PVA adhesive to swell, which enables the restorers to remove the mattress fabric, which can then be peeled off properly. Although a small amount of the leather fibers is also lost in the process, this can be ignored in this case. Kristin Krupa and Inken Süß have observed that in some places the fabric comes off very easily, whereas in other places the mattress fabric is more difficult to remove. The restorers say: “This is particularly the case on original inlays, for example, which were applied to weak areas of the leather during the production of the gold leather or to a rectangular shape to complete the shape.” In such cases, the two have no choice but to carefully remove the fabric piece by piece with a scalpel. The next step is to re-map and clean the front and back. Tears in the back that were covered by the fabric are then closed and missing areas filled in. To do this, the restorers use a calfskin specially produced for the restoration of the gold leather wallpaper. They are working together with the Research Institute for Leather and Synthetic Materials (FILK) in Freiberg. They opted for a certified leather that is very close to the leather of the gold leather wallpaper in terms of the type of tanning and other parameters, such as fat and moisture content as well as pH value. Once the work on the back of the gold leather wallpaper has been completed, Krupa and Süß turn their attention to the front. There, the large areas of overpainting and incorrect colors are corrected. The original paint layer remains intact. A solvent is used to remove the retouching, which requires extreme caution. You limit yourself to the colored areas of the wallpaper and leave out the areas where the gold paint has been painted over and only make very slight corrections. In doing so, they repeatedly discover that the imperfections are very small, but the overpainting carried out in the 1950s was very rough and extensive. The restorers, on the other hand, only apply their retouching to the areas where the silver leaf layer is exposed.

In the final step, before the gold leather wallpaper can be reattached to the wall, the squares are sewn together using the saddle stitch technique with a double linen thread. A total of twelve squares form a composite, to the outer sides of which leather edgings are glued with parchment glue. The leather pieces are used to attach the gold leather wallpaper to wooden stretcher frames so that it can be reattached to the wall. The frames are built by a wood restorer. A system has been developed in collaboration with the monument conservator in which the lower leg of the wooden frame is movable so that the frame can also work with fluctuations in temperature or humidity. There are springs on the sides so that the frame can still move. This means that the leather can still move, as the castle does not have museum-like conditions and the climate often fluctuates greatly. A humidifier set up in the knight’s chamber helps, but the conditions are still not ideal from a conservation point of view. The conservators therefore opted for an installation that meets conservation requirements and at the same time meets the wishes of the castle administration for a simple solution for dismantling. This desire for a way to remove the gold leather wallpaper arose from the idea that they wanted to be able to act quickly and flexibly in the event of maintenance or renovation work, as well as rescue measures.
In their work, it was important to the restorers that it was still possible to see where the leather had flaws. They therefore neither embossed the leather used nor applied any paint. Only in the green areas of the gold leather wallpaper did they make a slight color adjustment so that the overall appearance meets aesthetic requirements. In doing so, they are following a path that has become standard practice for most other restorers. Inken Süß emphasizes: “We not only want to preserve the object, but are also obliged to preserve the history of the object.” She goes on to explain that intervention is only necessary if the work is in danger of being damaged. But the work should be carried out as carefully as possible, as the objects’ age can certainly be seen.

The work will probably be completed in around three to four years. However, it is sometimes difficult to set a timetable, according to the two restorers, as there are many factors that influence the work. For example, the COVID-19 pandemic has led to supply bottlenecks for certain cardboard, and other materials were also unavailable due to the war in Ukraine. However, production errors can also occur, as is currently the case with leather. Now we have to wait for slaughtering to take place. At the moment, Krupa and Süß are waiting for the leather, which is only produced in small batches, so that they can then reattach a section to the wall next winter. In addition, the restorers emphasize that each leather panel is also a surprise package, because you can never predict what to expect. Some pieces of wallpaper have only a small amount of paste over, while others are much more heavily pasted. In addition, you never know what will be revealed under the mattress fabric. But adversities in the castle building itself can also cause problems, for example the west wall had to be replastered first due to a bulge on the outside. As a final step, the restorers then plan to restore the area around the faience mantelpiece, but they cannot work with the frame system there. This is because the gold leather wallpaper around the fireplace is particularly intricate and the frames will not work in this area. The restorers have also come across new findings: they were able to prove that, at least on the west wall, the arrangement of the squares was originally different from the current state. Using a particularly striking panel, they determined that the piece was originally positioned further down. However, they were unable to draw any precise conclusions about the arrangement and put the gold leather wallpaper back on the wall as it had been removed. With the new method of application, the gold leather wallpaper will also have a similar effect as it probably had in the 18th century. The wallpaper was not fixed smoothly to the wall, but instead was wavy, which, in combination with the silver leaf and gold lacquer, certainly created magical light reflections in the candlelight.

By the way: the Louvre is due to be renovated due to many defects.