How do I clean mould off of my cultural artefacts?
Mould can be very damaging to a wide range of objects. Mould grows on organic materials when the relative humidity remains above 65% for a prolonged period. It is disfiguring, can stain and obscure the surface, or even penetrate through the whole structure of an object.
To help prevent mould growth, you should try to keep your valuable objects in rooms with low relative humidity and good airflow. Mould growth is most likely to start in corners and in cupboards where there is little air movement. External wall surfaces in a room are also likely problem areas due to condensation of moisture on the colder surface and also through rising dampness evaporating from the surface of the wall in some buildings. Mould can sometimes be found growing on the back of paintings and textiles hanging on external walls due to the trapped moisture.
Mould growth may be lessened by ensuring good airflow during humid periods with fans and by opening cupboards. Equipment that draw moisture out of the air can also be installed in a room but only work effectively if the room is kept closed. Likewise, the use of silica gel as a desiccant can only work if sufficient is placed the space to cope with the volume of air and any additional air which entering. In reality, this requires a great deal more than a small bowlfull of silica in a wardrobe-sized space.
Prevention of mould is preferable but if mould growth appears it can be cleaned off to some degree. Objects displaying fresh mould growth should first be dried off in a well ventilated area. Sunlight can also be used as the UV light in sunlight may kill some of the mould. Avoid the harshest sunlight in the middle of the day as this could dry and split wood on artefacts or accelerate the fading of dyes on fabrics and watercolour paint
There are sprays available in the shops for killing mould. Those that contain ethanol, water and orthophenylphenol can be used on non-painted surfaces.
The dry mould can then be brushed off the surface into a vacuum cleaner nozzle. A very soft brush should be found which cannot mark the surface.
NB: Killing the mould with sprays or UV light will have only a temporary effect if the artefact is put back into the same unsuitable conditions. There are always mould spores drifting in the air that will colonise suitable environments.
Mould is dangerous to your health - always wear a dust mask when dealing with mould growth
More information about mould can be found at the Library of Congress Website.
Colin Macgregor , Manager, Materials Conservation