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Preserving parchment becomes more difficult when pigments, inks, and illumination are added into the equation. Pigments do not dye parchment; instead, they lie on the surface of the parchment and so are rather fragile. The goal of restoring illuminated manuscripts should be to make them resilient to damage while altering them as little as possible. Each individual manuscript, and even each individual page, must be considered as a separate object with different aspects that must be taken into consideration. This in turn will help determine the best course of preservation or conservation treatment.
One of the best ways to become familiar with the variety of issues caused by various materials is to learn about how such manuscripts were made in the past and how they were subsequently treated in later years.
The best distinction between inks and pigments is that ink is a colored liquid while pigments are colored particles suspended in a liquid. Areas colored by pigments usually have multiple layers of pigments and other mediums. The most important aspect of preserving pigments and inks is to identify their composition. Some techniques are not suitable for certain pigments and will do further harm.
Identifying specific pigments is no easy task. Descriptions may be wrong or misleading and choosing the wrong treatment may cause irreversible damage.
There are two different ways to identify pigments: invasive and non-invasive.
These tests alter the manuscript in some way, usually by removing some pigment to test a sample. They are generally reliable but results are not always clear.
These tests do not alter the manuscript and are much better for conservation purposes than the invasive methods of identification. Some methods include:
Raman spectroscopy analyzes the molecular vibrations of the pigments and uses this data to map out its chemical makeup. This works on the notion that every substance interacts with radiation in different ways, and these differing ways if measured can help identify the substance without having to take a sample. Unlike other non-invasive identification techniques the results of Raman spectroscopy are much more certain. It is even possible to analyze a pigment beneath a glaze or other treatment.
Parchment is hygroscopic. As such, environmental conditions such as humidity must be kept under control. Pigments add another layer to the problem, forcing a preservationist to fit environmental conditions to two different (and possibly conflicting) sets of ideal limits.
These problems are further compounded by the fact that pigments do not dye parchment; instead, they lie on the surface of the parchment and so are rather fragile. Pressing an illuminated manuscript pushes the pigment down, altering the image itself and likely causing damage (such as a relief effect to the other side of the page) so it is very important to not put any pressure upon images on parchment, especially when it is wet. This fact also has to be taken into account when cleaning dirt from the image and when encapsulating or framing illuminated parchment for an exhibition. There must be enough room between the image and the protective surface (such as Perspex) that the image will not be subject to rubbing if the parchment should expand with rising humidity.
Consolidation is a process that can either strengthen the bond between pigment and parchment or add protection to pigments and other finishes from aqueous treatments. Strengthening the bond between pigments and parchment help prevent the pigments from flaking and pulling away. The challenge comes with achieving the best consolidation results while altering the object as little as possible. The material used for consolidation should be appropriate for the pigments, the parchment, and any other aspects that may be affected by the application.
Soluble nylon was used until the mid-1970s when concerns over the material’s stability emerged. Parchment size was then favored until the mid-1990s when leaf gelatin gained popularity. This is not to say that gelatin is always the best consolidant to use; no consolidation technique should be used without first considering the pigments and other materials involved, though. For example, gelatin causes white lead to become friable. This problem is compounded by the flexible nature of parchment. One solution to this particular problem is to use some form of a cellulose ether such as methylcellulose, instead of gelatin. Again, this is not necessarily the right choice for every situation.
There are a few basic requirements for any consolidation agent:
One device recently used in consolidation techniques is the ultrasonic mister. Created in 1991 by Stefan Michalski, this device lends itself well to consolidating materials that react badly with liquids. Gelatin is the preferred consolidant.
The ultrasonic mister is usually used in conjunction with a paper suction table to direct the mist at the media and prevent distortion. This is not the best treatment for illuminated manuscripts that have printing on both sides, though. In this case it is better to forgo the suction table and instead use the lowest setting on the mister and to monitor the process carefully.
Problems may arise if condensed mist falls onto the parchment from the nozzle so it is advisable that the device be placed on the floor or a similarly low level to coax mist to drain back into the mister instead of falling upon the parchment.
Traditional methods of removing creases and flattening parchment through humidifying have been detrimental to the state of any pigments, causing them to come off the parchment slightly. This is because the parchment and pigments take on and give off moisture at different rates, causing them to expand and contract at varying rates and thus loosening the pigment from the surface. This results in flaking, cupping, and cracking.
The question becomes whether flattening creased parchment to some extent will cause more or less damage to the image than would be caused by not removing the crease. Sometimes not flattening the parchment in some respect will lead to the further degradation of an image. In these cases some form of hydration is necessary. Due to the nature of pigments, though, it is desirable to avoid direct contact with liquid water. This can be accomplished with Gore-Tex.
Gore-Tex now has controllable pore size and can block out many liquids, including liquid water and many conservation chemicals. Water vapor can still pass through the pores, though, so it is possible to hydrate the parchment and remove a crease without introducing liquid water to the pigmented image. This can be achieved by sandwiching a manuscript in Gore-Tex in varying ways to achieve the desired results.
Repairing a tear in a parchment with images or text on it is more of a challenge than mending a piece of parchment that does not have any such issues. Care must be taken to not cover up or obscure in any way the image or the text. Materials such as Goldbeater's skin can be made transparent enough to do this but great care still needs to be taken.
The ethics of illuminated manuscript preservation involve the potential for adversely altering the source material during the course of the repair work. In order to ensure the integrity of the manuscript, great care must be taken during any preservation activity. Risk assessments should be made to determine the potential impact of preservation work on the manuscript, and weigh that against the potential benefits of the restoration work itself.