Hi MITRA,
I’ve had several people ask me about mold issues on egg tempera paintings. I understand that the porous, high PVC surface of an unvarnished tempera is more prone to mold (since moisture more readily enters in). My questions are:
– How detrimental is mold on top of a paint surfaces (both on other mediums generally, and egg tempera specifically)?
– Aside from taking the work to a professional conservator to clean, what can a person do? I’ve known people to wipe the surface with alcohol, which seems to work well in removing the mold; however I’m concerned it may compromise the paint film if applied to liberally (abrade with applicaiton, or sink in and lead to embrittlement). What about using Phenol?
– A person recently wrote me with this question and wondered how consequential mold was for past painters, given that they did not have climate controlled spaces. Do you know if mold was historically a big problem?
Koo Schadler
I do know that mold was a problem for fresco painters, including Michelangelo who is reported to have modified his plaster composition to help avoid such issues. Since Northern painters also were aware of these problems in fresco, I would have to assume that there were strategies employed in the tempera painter’s studio to reduce the chance of work being spoiled. Pigments themselves can provide a growth medium, if enough organic material is present. I have personally seen Ivory Black attract some really nasty spoilage in water-based paints.
Koo, I would worry about mold on tempera paintings both in the medium and the glue in the ground as they could easily become food for the mold and other organisms. This also invariable involved discoloration as well. Diluted ethanol is often recommended to be strrayed on the reverse of canvas to abate mold contamination but I would not advise adding it to egg tempera paintings, mainly because of the water content. I am not especially worried about the ethanol component so much.
Koo, I know in the past that you varnished your works with shellac, assumedly diluted in ethanol. Did you see any adverse issues due to the ethanol? I would not expect it to. I would not use diluted ethanol on any work that had a varnish as the water component could become incorporated into the varnish film and cause sever bloom.
Really, mold is a result of too high humidity. It cannot grow at moderate RH, although if it is already on the piece, lowering the RH will not remove the mold, only stop it from growing. Any rise in RH above something like 65% would reactivate the mold.
I have had major mold growth issues with aqueous pigment pastes containing bone black, and some yellow ochres, and green earths to the point where they stink to a high degree. The yellow ochre and green earths in question also grew so much mold that the their hue was displaced by the black of the mold.
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