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
Mold
Where do they come from?
Mold is one of the main biological risks to paper documents. It generally appears when humidity, heat, and poor ventilation create conditions favorable to its growth. It is often recognizable by spots of varying colors—black, green, white, pink, or yellowish—a powdery or fuzzy appearance, and the possible presence of mycelial filaments. It can also give off a characteristic musty odor. On paper, it weakens the fibers, impairs readability, and can cause significant material loss.
In the field of conservation and restoration, paper is particularly vulnerable to fungal attacks, while parchment is generally less susceptible, although it can be affected by high humidity or flooding. When a paper document is contaminated, treatment can be carried out directly or indirectly depending on the condition of the support and the sensitivity of the inks. The use of 70% ethanol is commonly mentioned in disinfection protocols, particularly as a treatment suitable for collections, because it limits fungal activity without systematically resorting to more aggressive processes.
The intervention must be carried out with caution, however, as a moldy document remains fragile and can lose fragments of material with the slightest friction or handling. Before any treatment, it is therefore essential to assess the nature of the substrate, the stability of the inks, and the extent of the contamination in order to choose the most appropriate method.
Good prevention, based on controlling humidity, temperature and air circulation, also remains essential to avoid the recurrence of mold.
How can they be detected?
On paper, mold is most easily distinguished by its surface population, appearing powdery or fluffy, sometimes with visible filaments, while other stains are often more homogeneous, embedded in the paper or linked to a liquid, rust, or dirt. They may also be accompanied by a musty odor and appear as black, pink, yellow, or other colored stains.
Signs that point towards mold:
Powdery, velvety or slightly downy appearance on the surface.
Presence of small filaments or an irregular pattern.
A spot with diffuse outlines, sometimes with a halo, rather than a clear mark.
A musty smell, especially if several documents are affected or if the room is damp.
Which makes one think of something else entirely:
An old water stain is often uniform, brownish, with a sharper edge and no fuzz on the surface.
A rust stain often follows a pattern of dots or halos linked to staples, paper clips, or other metal objects.
"Foxing", or paper pitting, often appears as reddish-brown spots, in small dots or diffuse patches.
A greasy or handling stain is generally smooth, without relief or a spore-like appearance.
These indicators are useful, but staining alone is not always sufficient, as certain biological or chemical alterations can mimic mold.
Useful checks:
Observe with a magnifying glass or under raking light.
Check if the mark is raised or if it remains strictly within the fibers.
Carefully test whether the dust detaches easily on the surface; dust that reactivates may indicate spore contamination.
If there is any doubt about active contamination, have it confirmed by a laboratory or a conservation specialist.
Engraving showing a halo in the upper left corner, and so-called "foxing" marks on the rest of the document.
Painted artwork with a rust stain in its center.
Endpapers of a book showing visible signs of water damage with active mold stains.
Que faire lors de moisissures ?
Les moisissures sur des documents en papier ou en parchemin doivent être traitées avec beaucoup de prudence, car elles fragilisent les matériaux et peuvent se propager rapidement à d’autres pièces. Avant toute intervention, il est indispensable d’isoler les documents contaminés afin d’éviter la dispersion des spores. Le traitement commence généralement par un dépoussiérage très contrôlé, réalisé dans un environnement adapté, avec une protection personnelle appropriée. Cette étape permet d’éliminer les dépôts fongiques secs sans enfoncer les particules dans les fibres du support.
Pour les documents en papier, le nettoyage se fait le plus souvent à sec, à l’aide d’outils doux et adaptés, lorsque l’état du support le permet. Il faut éviter toute humidification tant que la moisissure n’a pas été stabilisée, car l’eau favorise son développement. Si le document est très atteint, un traitement plus poussé peut être envisagé par un professionnel de la conservation, notamment pour retirer les résidus, stabiliser le support et évaluer les dégâts. Dans tous les cas, il faut éviter les gestes brusques, le brossage énergique et les produits ménagers, qui risquent d’aggraver les dommages.
Le parchemin demande encore plus de précaution, car il réagit fortement à l’humidité et à certaines manipulations. Le nettoyage doit rester très léger et contrôlé, car un apport d’eau ou un frottement excessif peut provoquer des déformations, des tensions ou des altérations irréversibles de la matière. Là encore, l’objectif principal est d’arrêter la progression de la contamination, d’éliminer les résidus secs et de stabiliser l’objet avant toute restauration. Après traitement, il est essentiel de revoir les conditions de conservation, car la maîtrise de l’humidité, de la température et de la ventilation est déterminante pour éviter une réapparition des moisissures.
En résumé, le traitement des moisissures repose sur trois principes : isoler, nettoyer avec prudence, puis stabiliser les conditions de conservation. Sur le papier comme sur le parchemin, l’intervention doit toujours viser à protéger le support sans le fragiliser davantage.
Si vous avez des doutes concernant des taches présentes sur vos documents, n'hésitez pas à demander l'avis d'un expert !
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