art guide

Conservation and Treatment of Oil Paintings

C. Fungus/Mold

The mold that grows on pictures is no different from the mold that grows on other things. The growth may be noticed as light or dark spots.

In oil paintings mold spots are likely to appear first along the cracks, but by that time the back of the canvas will usually be found to have heavy growth. Mold feeds on the materials in the pictures that it infests destroying some of it. This results in the paint getting pitted or otherwise marked. Ground and support are also weakened.


  • Mold is usually caused by excessive moisture, either in the atmosphere or from flooding. Mold will usually not grow unless the relative humidity in a room exceeds 60% during a long period and usually 70% for a shorter period.
  • Dust is another cause for mold growth. The mold spore is a common one that thrives in the atmosphere. Most surfaces that are not constantly scrubbed are apt to hold them.
  • Fungi or mold frequently feed on the binding medium, the sizing in canvas, or the paste in a lining. Treatment A painting affected by mold should be removed immediately from its damp environment. A conservator must first clean off the mold and then fumigate the picture with an antifungal agent. In order that the fungus does not recur, it is important that the paintings bekept dust free and in a dry environment.


In treating flaking paint, a conservator must infuse a consolidant into the flaking areas and then apply pressure/weight during drying. Certain adhesives may be thermoplastic in which case heat must also be applied to activate it. In cases where the paint is totally missing the conservator must first consolidate the surrounding paint and then fill the missing area with a filter.

The final stage would be to inpaint that area in order that the painting appear complete.

fig 1. Mold growing in an oil painting. In this case it appears as light spots.
 fig 2. Dark mold growth
 fig 3. Painting
 attacked by fungus.
 fig 4. After treatment.