Help, Saggin Linen!

[Richard Bingham]

Originally Posted by Julie Deane

. . . I recently have glued up to 36 x 48 inches on Dibond panels successfully. Also smaller wood panels. I've used either PVA glue or Liquitex gloss medium. With the wood, one needs to add a protective coat to it before gluing.

Julie, thanks for the vote of confidence. What I recommend is to "do what works", and test to make sure your methods are sound. If I contradict a suggestion, or make one of my own that doesn't "set well" with some readers, the test is the final arbiter.

Gluing raw canvas to a wooden panel, I would use rabbit-skin glue. Hide glues "draw". The easiest way is to temporarily tack the canvas to the edges of a wooden panel (that includes plywood) and saturate the canvas with glue. Some shrinkage is desirable, and the "draw" as the glue sets makes for a flawless interface. I would NOT apply a coat of any kind to raw wood, it's been my experience that a film of anything, shellac, varnish, "sealer", etc. interferes with the glue bond. If it were desirable to apply coatings to glue joints, you can be sure luthiers would do so when building instruments; they do not.

Di-bond and alumalite are faced with aluminum sheet, which makes a glue which becomes brittle (such as PVA) a questionable choice. Currently, conservators are not averse to gluing canvas to such supports with "Beva-Gel" which is also a modern option to traditional maroflage. It's marketed through Kremer pigments, and is mighty "spendy". The material is a vinyl-acrylic adhesive, not chemically dissimilar to construction adhesives used to set tile or hang heavy, fabric wall-coverings at a tenth of the cost. I have used these adhesives and so far in testing, they certainly seem adequate. These substrates would not be ideal for a support under raw canvas, although the adhesives would be suitable for gluing pre-primed canvas to a wooden panel, and in this case, a coat of sealer would be necessary to keep the wood from absorbing too much of the adhesive - I believe this is what Julie had in mind in recommending an isolation coat over wood. RSG would NOT be a good choice for adhering pre-primed canvas to any support material.

Using acrylic medium would be functionally very similar, although with an attendant high cost.

??? Who knows what the likely failure modes and life-span for urethane and styrene foams will be? They are essentially stable, the foam makes for a structural cross-section, and they are not susceptible to decay from organic causes, or attractive to vermin. The only thing that seems to degrade them is UV, and that shouldn't be a problem as a support under a painting. I feel any difficulties the stuff will cause will occur long after they've laid lilies over the current generation of painters.

[Thomasin Dewhurst]

Thank-you Julie and Richard for your advice. My paintings are already painted - but unstretched - so I wanted to glue them to a board. The back of the canvas is raw (ish - it may have rabbit skin glue or something on the back - I bought it pre-primed). Could I used rabbit skin glue for that, or is it different for already painted paintings?

[Julie Deane]

Hi Thomasin,

I am sure Richard and I will have different ways to do this.

I've attached finished paintings as well as not-yet-painted, preprimed canvas to wood using PVA glue. The board was first given a coat of GAC100 to avoid any transfer of anything from the wood to the canvas.
I've not had any problems with the art staying firm to the wood.

Here's a link you might find helpful:
http://www.amien.org/forums/showthre...?t=1626&page=2

[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 . . .