Help, Saggin Linen!

[Richard Bingham]

Originally Posted by Thomasin Dewhurst

(. . . pre-primed). Could I used rabbit skin glue for that, or is it different for already painted paintings?

Pre-primed canvas or gluing finished painting to a panel, use acrylic gels, vinyl-acrylic adhesives, PVA or whatever turns your crank.

Gluing raw canvas to a wooden panel, you first tack the canvas to the panel, then saturate it with RSG from the front, this works well, and nothing will "transfer" to the canvas from the wood (?) because it's isolated by the glue. You can't do this with a pre-primed canvas or a finished painting, and while it is theoretically possible to use RSG for that pupose, it isn't the easiest stuff to use this way, and is not an appropriate adhesive to use over aluminum, or sealed wood.

Julie, just curious . . . what elements do you perceive "transfer" from wood to canvas, permeating an adhesive layer ? I know some plywood glues contain formaldehyde and other volatiles which may migrate or "off-gas", possibly reacting with other materials, but any solid woods suitable for the purpose (properly cured cabinet grades)are pretty much inert. Poplar panels were preferred from pre-Renaissance times by reason of several advantages that species presents for this application (broad planks, machineability, fine grain, low resin content, and optimal acceptance of glues and paint coatings.

[Julie Deane]

Richard, I don't know a lot about all this, so I'm just following advice I've read and being extra cautious.

According to the Amien site:

GAC 100 is an acrylic dispersion medium developed to prevent SID ("Support-Induced Discoloration), wherein the application of an acrylic dispersion ground -- around 50% water at the outset -- can dissolve organic materials in the fabric support and cause them to migrate into the drying ground and discolor it.

So I got it backwards: it's not from the wood to the canvas, but vice versa.

[Richard Bingham]

Thanks, Julie. That's interesting. What I gather from this, is that it is possible water-soluble contaminants/colorants inherent in a canvas could come into solution when an acrylic, water-soluble ground is applied, which would present as discoloration, or variegated stains or watermarks in the painting ground. The sealer you recommended (GAC 100) is a product intended to "pre-prime" a suspect canvas before applying an acrylic painting ground, to prevent any such discoloration.

Going back several responses in this thread, I'd say that the best prevention for this fault would be, as noted, wash your raw fabrics before stretching and priming them! .

I don't think one need worry at all about anything on a wooden panel discoloring either pre-primed canvas (especially oil primed) or a finished painting, although the sealer could be useful to control the absorption of PVA or acrylic adhesives by a raw wooden panel. ?? In any case, it sure can't hurt anything . . .