Q: I have a dry (painted 3 yrs ago) oil painting on stretched canvas. Can I use acrylic paints and mediums over the top? I know that technically it is recommended not to paint acrylic over oil, but I wondered if I used a medium instead of water whether that would get around the problem of cracking.
A: I am afraid we do not have any good news as far as painting acrylics over oils (even well dried ones!!!) It still is not recommended as the two systems are just not compatible over the long term.
It is simply a question or, due to, different drying ratios. Oils dry by oxidisation and continue to expand and contract as they dry. Acrylic media does not, it dries very quickly and quits flexing immediately afterward. This would manifest in your acrylic layer cracking and peeling (delaminate) over time since it cannot keep up with the oxidisation process under it.
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