The paper restorers at the National Gallery of Denmark have begun restoring and preserving the museum’s unique and previously inaccessible Gottorfer Codex: a four-volume flower book dating from the 1600s, from Gottorp Castle in South Schleswig.
A brief description of the work.
The Gottorfer Codex consists of 4 books with paintings of flowers and useful plants. It was created using gouache on parchment and measures 50.5 x 38.5 cm.
The entire work contains a total of 365 painted leaves with more than 1,200 illustrated plants, spanning species and varieties of ornamental and useful plants from the entire world, such as: asparagus, stinging nettles, sage, tulips, irises and fig.
The books are covered with brown leather, and the first and last pages feature the Gottorfer Castle coat of arms printed in gold. The books have a gilded spine and gold-leaf on the covers.
The sheets are bound on 8 raised double strings and all bindings have hand-stitched headbands. The bands have a dual purpose. They serve both to strengthen the top and bottom of the books' spines whilst also serving as a decorative function.
A protective paper sheet is inset between every painted parchment leaf. As the name indicates, protective insets can serve to protect the paint layer against wear, but are now used primarily for aesthetic reasons. All protective inserts will be stored together with the other material "left over" once the books are taken apart.
Floral works – not mere book illustrations
Dissembling the Gottorfer Codex (initially volume 1) has presented a dilemma to the restorers. The work has existed in book format for more than 300 years, but to preserve the floral paintings it has been necessary to remove the leaves.
Once the restoration is complete, several of the leaves will remain as individual works that will not be bound. Meanwhile this means that the book binding, protective inserts, parchment strips and binding string will not be discarded. All material is being archived because it provides extensive information on book binding techniques and use of materials at the end of the 1600s.
Opening a secret treasure
The book bindings are very worn, but have protected the painted parchment leaves from light damage. The flower materials have been closed inside the books for more than 300 years, and so opening the books today is like uncovering hidden treasure. The flower materials are from 1649-1659 yet appear with a clarity of colour as though they were from 1959. If these works had been exhibited during the same period, the colours would have faded and the balance between the different colours would be compromised, or in the worst case, completely erased.
The binding has protected the leaves from wear and light, but at the same time it has created the very damage that the restorers now hope to repair. The leaves are cockled, folded, roughly cut, have spots from colouring of the edge and a colour layer that is crackled.
Difficult to open
The books are difficult to open because the spine is glued with an animal glue that makes the book binding open very stiffly. To be able to use animal glue, one has to warm it up in a water bath (glue pot) and when the glue dries it is very stiff and extremely strong. Animal glue was used in the bookbinding trade all the way up until the introduction of synthetic glues in the middle of the 20th century, as there were no other alternatives, except for rubber cement, which was not particularly strong.
The leaves have been assembled into their bound form, two by two, using one strip of parchment. Gluing along the edges means that after drying, the parchment settles in a cockled state. It is these cockles that the restorers hope to straighten out. Before this can take place, the leaves need to be loosened from the book block, and the parchment strip and animal glue must be carefully removed from each individual leaf.
Grinding the edges
After having looked into various methods of removing the animal glue, the restorers found that the most gentle method was to remove the glue in a dry state using a small grinding tool and a scalpel.
In the greenhouse
Once the glue is removed, the conservator can start straightening the parchment out. The parchment especially needs to be straightened along the left edge. This is done by placing a slightly damp piece of paper under the left edge, and then setting up a “greenhouse” over this so that the moisture does not evaporate too quickly. Once the edge is moistened, one can begin carefully pulling the parchment using a clamp attached to a Velcro band and a stretcher that the Velcro can be attached to.
Crackling in the colour layer
The leaves cockle and twist when trying to turn the pages. The stiff binding and poor adhesion between the parchment and the paint layer means that the books cannot be used without risk of the paint layer cracking and flaking as the pages are spread. The paint layer is therefore cracked in many places and has completely fallen off in some areas due to previous use. These areas shall be secured with an adhesive (methylcellulose in ethanol) so the paint layer is consolidated on the parchment.
The crackling is not necessarily a problem if the paint layer is still attached to the parchment. It will only be consolidated if it has come loose.
Wear prior to binding
Several of the leaves show signs of wear that could not have occurred whilst the leaves were bound. According to the Gottorp accounting archives, it also appears that the paintings were first bound considerably later than their time of creation. One account from the archive in particular shows that the Schleswig bookbinder Paul Winter was paid for binding these leaves in 1690. This presumably means that the leaves had been lying loose on top of one another and therefore could have caused wear to the paint layer in several places. In most cases the restorers have elected to let this wear remain as part of the work’s life history.
The bookbinder also caused damage to the paintings in several areas. This can be seen in the form of stains from the colouring of the cut edge on the book blocks. The restorers have considered scraping the colour spots off with a scalpel and then trying to bleach the parchment, but bleaching can entail risk, as the colour has sunk down into the parchment. It was therefore decided not to remove the spots in these areas.
The bookbinder cut the leaves in such a way that they would fit into the same format. As a result of this, one can see several leaves where the motifs are missing along the edges. Others were folded, because the motifs were too large for the format chosen by the bookbinder, and in the folds where the parchment was bent the paint layer has come off.
It is not known why the bookbinder chose to cut the parchment leaves so drastically, but some of the leaves have been exposed to water damage and show signs typical of discolouration caused by mildew growth. It may have thus been necessary to cut the areas affected by mildew off.
The parchment leaves are very sensitive to fluctuations in relative humidity (RH) in the environment in which they are stored. This means that the restorers are very careful when exposing the works to moisture. The leaves must therefore be moistened slowly so that the parchment and the paint layer can react to the moisture at the same rate. It is especially rapid changes in RH that can cause the colour layer to crack and flake off the parchment. The preservation workshop is therefore climate-controlled and has a temperature of 22 degrees Celsius and a RH of 50%. The books must also be kept in the same climate conditions when exhibited, studied in a reading room or kept in the storage facility.
The parchment reacts relatively quickly to changes in RH, which is why showing the works will always entail a degree of risk. Access to the Gottorfer Codex has therefore been strictly limited over the last 15-20 years. Because of their fragile condition, the books in their current condition can no longer be used for either research or exhibition purposes. The National Gallery of Denmark has therefore set about to restore and preserve this work.