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spots on back of oil paintings?


  • It could be something from the paint that's coming through the canvas, or it could be black mold spores on the back of the canvas itself (which doesn't look sealed).
  • I used raw canvas and the following formula:
    1/2 cup of water
    1/2 cup of plaster of paris
    1/2 elmers glue
    1 cup of white acrylic paint

    3-4 coats on it.  I think I'm going to buy some dick blick studio canvas pre-made and stretch it so this doesn't happen again. 
  • coated before or after stretching?
  • Have you painted on the canvas, or is this just from your gesso formula?
  • Yes I have painting on the canvas using oils.  Is it safe stretch primed canvas?  It's either do that or buy some GAC 400 and 100
  • sonnystrauss

    Yep. I agree this looks like mold.

    Imperative that you dry out your studio and storage areas asap.  These spores spread through the air with little encouragement. 

    On the back of the painting: It is preferred to attempt mildew removal from the back of the surface so you do not damage the paint. You do not want to saturate a canvas, but lightly mist it with one of these to stop mold growth:

    • Lysol (a brand of anti-germ/bacteria cleaner - the spray and not the liquid form) is recommended by the New Orleans Conservation Guild.
    • Commercial rubbing alcohol (70% alcohol) mixed with water in a fine mist spray bottle is recommended by MOMA.


  • Yes it's OK to stretch canvas and linen after it is primed. Many painters complete their paintings before stretching.
  • dencaldencal -
    edited May 2017

    Looking as close as I can, these spots look more like you have laid this canvas on a wet painting.
    The spots have a greenish cast and the alignment of some spots suggest paint and there are smudges of white. Check it out with a magnifying glass.

    Mold can be green, but damp Mold is usually black.


  • Is it possible, that in the warehouse these canvases were sprayed with gesso with an industrial airbrush and it malfunctioned, spewing out the built up from the inside of the sprayer? Sometimes this happens in airbrushing, often what spews out is something similar to this example. Manufacturing defects! 
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