PHYSICAL CONDITION Initially the illuminated folios were brought to the lab because severe planar distortions prevented the safe reframing of the works. The folios were framed in a velvet covered, wooden liner in a gilded frame with glass glazing (fig.1). The parchment had completely detached from the backing to which it was once attached, popped forward in the frame, and was touching the glazing. The distortions are related to the inherent nature of parchment, which is cured rather than tanned like leather, making it very sensitive to changes in humidity. Even when stretched, parchment retains a memory of the animal it came from and acts like a hide. Changes in humidity levels induce expansion and contraction of the support resulting in planar distortions. These distortions become more pronounced with each introduction of improper humidity levels. The folios had been displayed in a climate with high and fluctuating humidity in a building without artificial climate control.
St. Christopher folio exhibiting extreme planar distortions in the old, gilded, frame with a decorative velvet-wrapped wooden liner and glass glazing.
Detail of mold damage to parchment and paint layers in the Pentecost folio before treatment.
Surface soil, soot, and grime were present on the rectos and versos of the folios and the high humidity levels instigated mold growth. The mold fed on the parchment, causing red-brown foxing stains which were scattered throughout the parchment and a few areas in the paintings. The mold damaged parchment was spongy and weak (fig. 2). Old attachments, gummed brown paper tapes and tabs of pressure sensitive foam tapes, were attached to the top and bottom verso edges of the folios for mounting the folios onto backing boards. The attachments caused localized staining, locally intensified parchment distortions, and the gummed adhesive provided an additional food source for the mold. The thickly applied media was beginning to crack, flake, and powder in areas and was the most concerning condition issue. In the case of the folios, expansion and contraction of the parchment in response to fluctuating humidity levels, was constantly inflicting stresses on the physical bond between the paint and the parchment. The physical tension induced detachment and minor losses of the paint from the parchment. Powdering of paints, which was also observed in the folios, occurs when there is not enough binder to hold the large pigment particles together or if the binder degrades, no longer providing the necessary cohesion. In the 1400s, paints were made by hand by the artist or their studio which meant that the results were less standardized. Making a paint with enough binder required experience and sensitivity to materials. Improper binder to pigment ratios is a common condition issue for pigments with larger particle sizes. Examples of such pigments used for manuscript illuminations are malachite, azurite, vermillion, and ultramarine. Examples of media damage are shown in the slideshow below.
CHEMICAL CONDITION ISSUES Light and air pollutants interacted chemically with the works, causing fading or darkening of select pigments. Darkening of lead white paint was present in the paintings which altered their appearance. Darkening of lead white paints mixed with water-based binders is caused by a chemical reaction in the lead white when exposed to sulfurous air pollutants. This condition issue was found in all of the folios since lead white was used extensively in the illuminations. The most dramatic, and visually disruptive examples of lead white darkening were found in St. Margaret’s face and St. Pope Urban’s hat and robes (figs. 3-4).
Lead white darkening in St. Margaret’s face.
Lead white darkening in St. Pope Urban’s hat and robes and in the stone architecture above him.
Fading of organic pigments was noted when comparing the rectos and versos of the same folio. Organic pigments are very susceptible to light exposure. Energy from light breaks the chemical bonds in the organic pigment molecules producing a different organic molecule. The new degradation byproduct has different chemical properties that directly affect the color of the pigment. This chemical change is expressed visually as a shift or loss of color—fading. The organic red pigment has been the most severely damaged by light exposure. Organic red paint on the verso of the folios has a richer purple-red color and has much more density than the same pigment used on the rectos (see the comparison in (figs.5-6).
Organic red pigment on the recto of the St. Mark folio exhibiting noticeable fading in the bar spacer and the second tier illuminated letter ‘B’. Evidence of faded iron gall writing ink is also present on the recto of this folio.
High light levels will cause Iron gall ink to fade. Evidence of ink fading is apparent in the folios when comparing the ink on the protected verso side to the ink on the displayed illuminated side (figs. 5-6). Minor to moderate loss has occurred because of cracking, flaking, and powdering of the ink (fig. 7). It has also begun to sink through to the verso side, obstructing the legibility of the text on that side. The ink degradation is also causing the pigments in the illuminations to darken, particularly the lead white. Fortunately, research has shown that collagen and alkaline pH levels slow iron gall ink degradation. The alkaline processing of parchment and the fact that it is composed of collagen has a direct, positive impact on the long-term preservation of manuscripts.
Iron gall writing ink exhibits characteristic degradation which is inherent because of the components used to make the ink. During the medieval era, there were no formalized recipes for making iron gall ink and the process of making the ink was not scientifically precise. Often, the inks have excess, unbound iron ions and acidity present. The un-reacted iron compounds are highly reactive and catalyze a corrosive chemical reaction. The degrading ink will also chemically degrade the support, in this case parchment made up of collagen, causing it to become discolored, acidic, and brittle. The ink will burn through the support eventually causing losses in the support where the ink was once applied. Exposure to improper environmental conditions such as high and cycling humidity, light, and temperature levels also contributed to the degradation.
Organic red pigment on the verso of the St. Mark folio has significantly less fading compared to the same pigment applied to the recto. Evidence of faded iron gall writing ink is also present on the verso of this folio.
Detail of cracking, flaking, and losses in the iron gall ink.
TREATMENT AND PRESERVATION Consolidation Treatment of the folios began with stabilizing the cracking, flaking, and powdering of the media to prevent further losses. Funori, a carbohydrate seaweed extract, was selected as the ideal adhesive for consolidation (fig. 8). Funori forms a matte flexible film of moderate strength that has been used for centuries by Japanese scroll mounters to consolidate powdering pigments. The matte finish of the funori was ideal because it matched the matte finish of the paints in the illuminations and would not change the appearance of the consolidated areas. Flexibility of the funori film is important for maintaining cohesion of the treated areas if the parchment is flexed or during any dynamic dimensional changes caused from improper humidity levels. The two-brush consolidation method was used to treat the unstable paint films (fig. 9). This step was done with the aid of a microscope for optimal control. A minimal amount of ethanol was applied to the damaged media to reduce surface tension followed by a second brush charged with a small amount of funori applied to cracks and edges of flaking pigment. Reducing surface tension allows the funori to penetrate more effectively into cracks, under flakes, and around powdering pigment particles. Gentle pressure was applied to the consolidated area to encourage contact between the paint and the parchment as the funori dried. The consolidated areas were checked for stability during the process applying funori several times before the detaching area was secured. Degraded iron gall writing ink was consolidated with the same procedure but using a 0.5% (w/v) solution of gelatin instead of funori; the added benefit of collagen protein in gelatin slows the degradation of the corrosive iron(II) ions in the ink.
Funori was used to consolidate flaking and powdering paints. Slightly processed funori is on the left and fully processed funori is on the right. The fully processed funori may be rehydrated upon use for treatment.
Associate Paper Conservator, Brook Prestowitz consolidating flaking media using the two-brush method under magnification. Photo taken by Rebecca Johnston.
Surface Cleaning and Structural Repairs Surface soil and mold residues on the parchment rectos and versos were reduced with a kneadable eraser, avoiding all media. A microscope was also used in this step for accuracy. Accretions, which are surface deposits of foreign materials, were reduced mechanically with a scalpel. Old paper attachments were removed from the versos of the folios using a heated spatula to remove the foam tapes. A 4% (w/v) methylcellulose aqueous poultice was used to remove paper tapes. This was followed with a gentle enzymatic solution applied by cotton swab to reduce gum adhesive as best as possible without introducing too much moisture to the parchment. Small tears in the parchment were mended with Japanese Kozo (paper mulberry) tissue paper adhered with 5% (w/v) gelatin or wheat starch paste.
Reduction of Planar Distortions The distortions in the folios prevented safe matting and framing of the works because the surface of the paintings would touch the glazing. Contact with the glazing could cause further media damage and loss. Planar distortions in paper and parchment supports are reduced by relaxing the fibers and slightly expanding the hygroscopic supports with controlled introduction of moisture followed by drying under pressure or tension. Exposure time and the methods for introducing moisture are also important for success. Parchment supports pose an additional challenge because of their extreme reactivity to moisture. If parchment becomes too wet, it can easily revert to raw flesh. Most importantly, humidification and flattening should not cause damage to the support and media, so the conservator must choose techniques keeping the vulnerabilities of the artwork in mind. The goal of this treatment step was not to completely flatten the folios but to reduce the distortions enough to safely mat and frame the folios. The humidification of the folios needed to be done very gradually to avoid disturbing the fragile attachment of the paint layers to the parchment. A humidity chamber was used to humidify each folio because it offers the most control over the introduction of moisture and allows the work to be monitored during the process. The folio was supported by a screen over a reservoir of deionized water in a tray. Plexiglas was placed over the tray to seal it and allow humidity levels to rise. Tension drying was chosen to flatten distortions. Linen threads were attached at even intervals along the verso edges of the folios using 8% (w/v) gelatin. Threads would also be used in a later step to mount the works for display. After a brief thirty minutes of humidification, the folios were removed from the chamber and dried under tension. The free ends of the threads were secured with masking tape to an 8-ply window mat ‘stretcher’ to relax distortions (fig.10 a-b) as the parchment dried. The threads were examined periodically as the parchment dried, adjusting the tensions as needed.
FIGURE 10a .
Paper Conservation Department Head, Rebecca Johnston preparing the humidified folio for tension drying on the 8-ply window mat ‘strainer’. The open humidity chamber is to the left of Rebecca. Photo taken by Brook Prestowitz.

FIGURE 10b .
Adjusting the tension on the linen threads as they parchment dries. Photo taken by Brook Prestowitz.
Cosmetic Treatment Once the chemical and physical stability of the folios was ensured, cosmetic treatment steps were completed to address issues that were disrupting the aesthetic appreciation of the work.. Darkened lead white was converted from lead sulfide to lead sulfate using a 3% (w/v) solution of hydrogen peroxide at pH 8. The solution was brush-applied in very small quantities using a microscope to ensure accurate application and to monitor the reaction. The shift of the darkened lead white from black or dark gray to pale gray or white, significantly improves the appearance of the image and, most importantly, honors the artist’s original intent. The most notable results are seen in St. Margaret of Antioch and St. Pope Urban (fig. 11 a-b, fig.12).
FIGURE 11a .
A detailed comparison of St Margaret of Antioch’s face before treatment (11a) and after (11b) applications of 3% hydrogen peroxide at pH 8 to convert darkened lead white.
FIGURE 11b .
A detailed comparison of St Margaret of Antioch’s face before (11a) and after (11b) applications of 3% hydrogen peroxide at pH 8 to convert darkened lead white.
St. Pope Urban folio after applications of 3% hydrogen peroxide at pH 8 to convert darkened lead white.
Another cosmetic step addressed the most prominent and distracting mold-related foxing stains within the paintings. The stains were masked with powdered pastels applied with a dry brush. The goal of toning the stains was not to make them disappear but to mute the staining to a point that they were less visually disruptive (fig. 13 a-b). Pastels were an ideal media for masking the stains because they emulated the matte finish of the original paints. They also remain easily removable if necessary.
FIGURE 13a .
Comparison of mold staining in the painted image before cosmetic treatment (13a) and after applying pastel to reduce the appearance of staining (13b).
FIGURE 13b .
Comparison of mold staining in the painted image before cosmetic treatment (13a) and after applying pastel to reduce the appearance of staining (13b).
Matting and Framing The folios were matted and framed after treatment in preparation for display by the client. Each folio was humidified for a second time in the humidity chamber then secured onto a 100% cotton rag, buffered, 8-ply mat board by adhering the opposite, detached ends of the linen threads to the mat board with Jade® R PVA adhesive. This unique mounting system was selected because the linen threads will help to mitigate any moisture-related dimensional changes in the parchment (fig. 14). Linen threads shrink in the presence of high humidity unlike parchment, which expands in the same conditions and vice versa in drier conditions. The reciprocal responses to humidity levels of the two materials will help maintain the proper tension on the parchment to prevent planar distortions from developing in the future. This dynamic mounting technique will also prevent splitting or tearing of the parchment if extreme changes in moisture occur.
St. Pope Urban folio mounted with the linen thread technique and ready for matting and framing. Photography by Stephanie Gold and Lila Reed
A decorative window mat was created using preservation quality materials to retain some of the more decorative aesthetic of the previous matting and framing. The mats were built up to a depth that created a protective amount of space between the folios and the glazing. Each matted work was placed onto Coroplast™, corrugated polyester, backing board and TruVue’s Museum Optium Acrylic® glazing was placed over the mat. Next, the edges of the frame contents were sealed with 3M™ 850 silver tape which has a polyester carrier lined with aluminum foil and coated with acrylic pressure sensitive adhesive. This is called a sealed package which creates a protective microclimate that will buffer changes in environmental humidity and temperature (fig. 15). The seal created by the tape will prevent or slow infiltration of water into the folios in the event of floods or pipe bursts. Since parchment is so reactive to moisture, the sealed package is a key asset in long-term preservation.
The recto and verso of two sealed packages. The corresponding text on the folio’s verso was printed and attached to the frame verso for reference.
The folios are also protected from dust and air pollutants in the microclimate. This is beneficial for preventing further darkening of lead white pigments extensively used in the artworks. Finally, Museum Optium Acrylic® is the most advanced technology for glazing framed works of art. It is scratch resistant, glare resistant, does not build up static charge, and filters UV light. Mindful display of the works will also help with the long-term preservation of the works. It is important to note that even visible light will cause damage to light sensitive pigments and degrade parchment over time. The sealed packages were installed into beautiful custom, hand-gilded, wooden frames that interact sympathetically with the illuminated works (fig. 16).
The St. Ives folio after treatment, mounted, sealed, and secured into their gilded wood frames.
The folios were displayed in a room with year-round climate control. Artificial lights are turned off and window blinds are closed when the room is not in use to manage light exposure. The next slideshow shows all the folios after treatment and before matting and framing.
Photography Credit | Brook Prestowitz, Rebecca Johnston, Matthew Hamilton, Maggie Barkovic.