I would like to collage on top of oil paint. I have only ever used acrylic mediums before, and they are not supposed to work on top of oils. Would your MSA varnish and/or gel work? They seem like the best solution, but I wonder if you have any information about it...has anyone tried it?
The MSA Varnish can be applied over cured oil paint films, so there is no problem there. We suggest a couple of coats of MSA Gloss Varnish, and let them dry for at least 24 hours. Once they are dry, you should have adequate adhesion for collaging with waterbased acrylic mediums, such as Matte Medium, Soft Gel Gloss, and most products you have probably used for standard applications. Once the collage is complete, seal the entire piece with Soft Gel Gloss (2:1 with water) and then apply either the MSA Varnish or the Polymer Varnish as the final removable coating. We would suggest you document this procedure somewhere on the backside of the artwork, NOT ON THE CANVAS, but perhaps a small paper tag glued onto the stretcher frame, so future conservation can be attempted with complete knowledge of the procedure.