I wanted to check something with the experts. I was told a few years ago that an artist was told by a restorer that on very old oil paintings they use acrylic for the repairs. I assume this was done to be a visible repair so as not to pretend to be the original painting. But the artist I was talking to, interpreted this to mean that if the oil is fully dried then you can use acrylic over it.
I wanted to check if a fully dry (2 years or more) oil painting will accept acrylic and create a stable painting. And that leads to someone asking me about putting acrylic primer over an oil painting. She said she thinks it is not a good idea but that all her artist friends assure her it is what they all do to reuse a surface.
Would it make any difference to use the acrylic over a varnish, would it be better or worse?
The acrylic-based colors used for inpainting repair is usually acrylic solution paint (solvent-borne) rather than acrylic dispersion (water based). Similar to the retired product Magna, acrylic solution conservation colors are formulated for reversibility, not permanence. Regardless of the assurances of your associates, I recommend you follow your instincts and prime fresh canvases, instead of risking new work on reclaimed old supports. The savings realized by reusing old oil paintings is very small, and the acrylic primer will not achieve anything like the adhesion it would with new canvas. (For sketches and exercises, I sometimes prime the reverse side of failed paintings, but these are not intended for presentation.)
Matthew is right. Those colors are essintially pigments ground into the same solvent borne acrylic mixtures as MSA varnishes. The adhesion of these is vastly different than acrylic dispersion colors.
