Mold spores are everywhere. They grow rapidly in warm, humid, dark surroundings and feed on a variety of materials often found in close association with paper artifacts—starches, glues, vegetable gums, even the cellulose itself. The results are all too familiar: patches of fuzzy growth, unsightly stains, and sometimes even partial loss of medium. The pastel portrait shown here is a case in point. A mold organism has consumed the gum tragacanth binder which holds the powdery pigment particles in place, leaving them loosely seated on the surface of the paper.
When mold growth is present in an artifact, a conservator should deactivate it as soon as possible. Afterwards, it can often be aspirated or vacuumed from the surface. Where appropriate, a carefully selected bleach may be employed to decolorize stains. After treatment, the conservator may recommend that displaying or storing the artifact in an area with controlled temperature and humidity to minimize the potential for future mold growth. Sealed, climate-controlled housings are another alternative, especially in cases where environmental control is not available or not dependable.
The intaglio print of a horse shown here exhibits another consequence of high relative humidity, known as "foxing." The cause of these amorphous spots is not yet fully understood. One theory is that metal particles in the paper begin to corrode, thereby creating voids that attract moisture, ultimately resulting in mold growth. What we do know for certain is that a controlled environment will slow or halt foxing, so the same sorts of measures used to discourage ordinary mold outbreaks are advised.
NEXT PROBLEM