Exhibition presented by Carole Jeanneret
from the "Open Book" workshop
24 Rue de Lausanne in Fribourg
"The mission of the conservator/restorer: what if your books could last another 100 years?"
From June 3 to 27, 2026 at L'Atelier, Place Notre-Dame 16 in Fribourg
The stains
How can we identify stains on our papers?
Common stains on old documents: foxing, halos, and mold.
Old documents made of paper and parchment frequently exhibit visual alterations that reflect their history, their state of preservation, and the processes of degradation. Among the most common are foxing, staining, and mold. Although these three phenomena can appear simultaneously, they differ in their appearance, origin, and impact on preservation.
Correctly identifying the type of stain is essential for choosing the appropriate conservation strategy:
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It is an age-related alteration, often stable, for which treatment is limited.
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They result from localized liquid contamination and are often indelible.
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They represent a challenge for collections and require urgent intervention and rigorous control of storage conditions.
In all cases, a thorough preliminary analysis and tests are essential before any intervention, as each document reacts differently depending on its composition, condition, and history.
Foxing
Foxing (from English, sometimes translated as "foxing" or "prickling") appears as small yellowish to reddish-brown spots, often irregularly shaped or rounded, scattered across the surface of the document. Foxing appears mainly on old papers (books, archives, engravings, stamps) and worsens over time.
Two origins are possible:
- a mixture of rag pulp and wood pulp in papermaking. The fibers of wood pulp paper contain lignin, which is unevenly distributed throughout the paper sheet. These fibers react to sunlight and oxidize, resulting in very localized yellowing or even browning known as "foxing." This can be compared to freckles on paper.
- The presence of fine metallic particles in paper pulp, which, over time and with exposure to sunlight, oxidize and turn yellow to brown. This produces the same visual result as the case described above. The presence of these metallic particles in paper pulp appeared as soon as paper manufacturing became industrialized. Metal hammer mills were replaced by metal Hollander batteries, leaving metallic residues in the paper pulp.
Can we intervene and remove them?
This visible chemical phenomenon is unfortunately irreversible. However, pH adjustment through treatment and limited sun exposure are very effective techniques for significantly slowing down this phenomenon.
For this, don't hesitate to ask a professional for a suitable treatment. A deacidification bath can be performed to temporarily stop the phenomenon and slightly improve readability.
The halos
Halos are weighted, diffuse spots, often circular or fan-shaped, usually brown or yellowish in color. They typically appear around a localized source of contamination (water droplet, ink, glue, greasy fingerprint, spilled liquid). Unlike foxing, halos are generally more extensive and follow the paths of the liquid's migration through the paper fibers.
Can we intervene and remove them?
The stains are often permanent because the substances have penetrated deep into the fibers. Their treatment is complex and may require localized aqueous cleaning or, in some cases, accepting the alteration to preserve the integrity of the document.
The older the halo, the less it can be reduced; conversely, the more recent it is, the greater the chances of reducing it.
Halos are identified by:
Mold
Molds are colonies of microscopic fungi that grow on paper in the presence of high humidity, favorable temperature and a lack of ventilation.
Unlike biological foxing (which contains fungal elements but remains localized), active fungal contamination by molds is dynamic and can continue to develop as long as humidity conditions are favorable.
Can we intervene and remove them?
Treatment requires quarantine, dry cleaning, sometimes fungicide treatment, and above all, correction of storage conditions (humidity control, ventilation). Unfortunately, mold stains often remain indelible and cannot be removed, but they can perhaps be reduced.
It manifests itself through:
Comparative table of the various possible tasks
