Rabbit Skin Glue - do you need it?
 

I have some stretched but unprimed canvasses waiting to be sealed with Rabbit Skin Glue, but I am put off by the awful smell of it when you heat it. Do you need to use RSG? Or can you just use gesso, which I believe has RSG in it, or am I wrong. What is the longevity of canvasses just primed with gesso?

I am afraid you need that RSG layer to protect and stiffen the linen fibres. You could use an acrylic size, but I tried it and didn't like it. Also I found the canvas would slack once the size was dry.
Just light a scented candle and go ahead :-)
Ilaria

I agree with Ilaria, the RSG tightens up as it dries and the satisfaction comes from the "drum" sound that you will hear when tapping the center of the canvas. Music to your ears! I wouldn't just gesso over raw linen, the fabric needs that protection, and isolating layer. I've never used the newer products but have heard from others the same complaints that Ilaria mentioned re slacking, and have seen it in another artist's beautiful painting. She must now remove it from an elaborate handmade frame and stretch a large painting, and may have to do it again.

Jean

I have an old painting from my college days that still sounds like a drum, over 35 years old (but the painting sucks!)

Thank you Thomasin for bringing this subject on the forum today.

Actually, I just bought raw linen, a binder that is said to be used for sizing canvases, and gesso.

I have not tried it yet, but reading these posts make me worry a bit. Has anyone tried modern binders that would not cause any problem of slacking? I hope so.

I am painting on a big canvas right now (100*140) that I bought a few months ago. It was already primed, and sounding like a drum at first. And it started to slack when I was working on it. I thought that I did something wrong, I didn't imagine that it could have been a problem linked to an acrylic sizing...

Anyway, I read somewhere a few days ago (have to remember where it was), that the product named RSG they were selling was not true RSG but acted as it was. Has anyone heard of it ?

Karine

If a canvas is to be prepared with any type of oil ground, natural fibers (linen, cotton, hemp) must be isolated against the absorption of oil with glue size.

Good quality RSG has no particular odor. High quality glues come in a fine powder best dissolved by pouring boiling water into a clean enamel container while sifting in the glue, just like making "Jell-O".

Coarser grades of hide glues (not necessarily from bunny-wabbits) can be rather malodorous. They come in pellets the size of coarse sand to wheat grains which require soaking overnight in water before heating to liquid and are not the preferred material for preparing a painting ground.

Proper proportions are six tablespoonfuls of dry glue to a quart of water (preps approximately 50-60 square feet of canvas). Cold glue can be returned to liquid by gently heating in a double boiler. It is unnecessary and inadvisable to "cook" hide glues, or to heat them beyond the low temps required to liquify them.

Initially, give the raw canvas a "drink" of half-strength glue. When thoroughly dry, apply full strength glue to the surface of the canvas, preferably just warm enough to be fluid. As it cools and gels, wipe your palm over the surface to equalize the application. Avoid saturating the canvas with full-strength glue solution - the first "drink" helps avoid that.

When the surplus glue cools, it will form a gel which can be frozen for later use, or refrigerated between uses for a couple of days. Do not use glue that is moldy, returned to a liquid while cold, or smells foul.

Some clarification. "Gesso" as we've come to know it in the 50 years or so since acrylic co-polymer artists materials have been commonly marketed bears no resemblance to the "real" gesso of the old masters, which is a compound of whiting, gypsum, and hide glue. It is too brittle for use as a painting ground on stretched canvas.

In general, acrylic primers are adequate to isolate natural fibers from oil absorption. Many painters feel the flexibility of an acrylic layer under oil paint is problematic for the longevity of a painting. (Violates the "fat over lean" rule.) Most preparations are quite abrasive, and really brutal on brushes.

Ah, Karine, we are cross-posting!

Some clarification. "RSG" stands for Rabbit Skin Glue. Yes, sometimes glues are identified as "RSG" and contain hide glues from other sources.

Possible confusion with "PVA" or Poly-Vinyl Acetate, a water-soluble synthetic glue, common brands are "Elmer's" and "Tite-bond". Some folks use it rather than natural hide glue.

In my experience, acrylic primed fabrics will "slack off" when worked on vigorously or otherwise manipulated. Cotton will tend to stretch with work, regardless of the method of preparation, and linen is particularly prone to changes in tension with changes in ambient humidity. Linen is deceptive to prepare because it shrinks so readily when washed, or in the first sizing. The "deception" is that it will draw up drum-tight regardless whether it is evenly tensioned on the chassis. Hemp is the least forgiving of sloppy or irregular stretching, although all stretched canvases will show the defects of initial preparation with age.

Thomasin,
In the past, I have used refined CMC (carboxymethyl cellulose) as an alternative to rabbit skin glue to isolate the raw canvas before applying an oil ground. It is odorless and doesn

Thank-you very much for all this information. It has been very helpful, and gave me the courage to go ahead and stop procrastinating.

I had some RSG from DickBlick which had to be soaked overnight, so I did that and then heated it the next day in the microwave on medium (I don't have a double boiler), stopping and stirring every 10 - 30 seconds to ensure it did not boil. It took about 10 minutes before the crystals were fully dissolved. I used that mixture straight (i.e. didn't dilute it), and a lot of it, for the canvas's first "drink", and found the canvas tightened almost immediately, and made the drum sound. I applied the glue along the sides and a bit on the back of the canvas too so it wouldn't bring raw canvas to the front when it shrank. So now it's drying, waiting for the second coat.

The RSG didn't have any odour at all, and I was marketed as true RSG. All very easy and enjoyable to do.

Two more questions: How many coats would you put on? And would you use ordinary house paint PVC on top? Would that be harmful?

You guys won't save a lot of money doing that in the U.S. it is much better to buy from Fredrix or Classens, but if you want, go for it!

Any acrylic base can substitute RSG, but this last one is the best.

Claudemir, the common objections of cost, and expenditures of time (better spendi it painting, instead of making supports) are certainly valid.

Anyone who preps their own supports simply to save money is definitely barking up the wrong tree, but I assure you that for my own purposes, neither Claessens nor Fredrix provide what I make up in my own studio. As they say on TV, "Not sold in stores!!"How important is that ? Not very in the long haul, probably, but it assuages my need to be totally in control of the process.

The unfortunate thing is that discussing the process online is bound to annoy some folks who prefer certain approaches or materials over others, and will not be thoroughly helpful to those trying to learn how, because although it's not rocket science, it's involved enough that the only good way to instruct a sound method for stretching and priming canvas is to see it done beginning to end.

Thomasin, the variables you indicate make it a real problem to answer your questions. That said, making the linen "drum tight" is not the purpose of sizing, and glue in too heavy a concentration, improperly applied is likely to cause problems. Not having ever used a microwave to warm glue size, I can only speculate that as microwave is known to change the consistency and character of many foods, it may or may not be advisable to use making glue.

Tensioning of the fabric through shrinking or stretching is an issue entirely aside from sizing. Coating or saturating the fabric with a heavy concentration of glue size is inadvisable. Think of the glue as being like a sheet of glass between the paint (and its oils) and the fabric. It is a barrier. The half-strength "drink" is applied to make it so a full-strength application will not saturate the linen, but remain on the painting surface as a barrier coating. One application is adequate if properly applied.

Now I'm confused. "PVC" may be understood to stand for Poly Vinyl Chloride, which is a plastic. House paints of any species have no place in the preparation of a fine-art painting support.

If you intend to use a water-reducible acrylic co-polymer "gesso" to prime a canvas, there is no need to use RSG at all.

Thomasin,
I don't know what is a double boiler, but here is the traditional way I learned to heat the RSG : in french it's called " au bain-marie". You don't need to make the water boil, the RSG souldn't exceed 60 celsius degres, or it will loose it's qualitys.

Marina, thanks for posting that picture. That's exactly the kind of "high-tech" double boiler I've always used . . . If hot water from the tap is at least 150F, that's adequately hot to liquify RSG that has cooled to a gel, using the "system" pictured.

RSG question
 

Hello everyone,

I have been using modern acrylic gesso up until now, but decided that I should try the older methods. So I made a mixture of RSG for several recent canvases. Not having done this before, I realized (too late) that I had made the mixture too rich. The canvases look fine now. But I am concerned that the glue might run into problems this summer when the humidity is higher. I wonder if there is a danger of mold. Is this something I should be concerned about? Is there anything I could do at this point to prevent future problems? I am wondering how forgiving the mixture is if you don't do it perfectly. Does anyone have previous experience with working with glue.

P.S.
I plan to use a lead based ground (Holbein) before I start painting.

Mary, future problems with RSG have less to do with mold or varmints than what a too-thick application to raw canvas does. Too much glue is brittle, and that's not good under oil paint.

The primary purpose of the size is to isolate canvas fibers from absorbing oil, solvents, and vehicles in the paint. Ideally, a solution is about eleven tbsp. of dry glue to a quart of water. The quality and fineness of the dry glue is a factor.

First, cut that glue solution by half, to give the canvas a "drink". When that's dry, apply full-strength glue to the painting surface only. Hopefully the "drink" will keep the canvas from becoming saturated through and through with full-strength glue. When the solution starts to cool and gel on the surface, smooth it out with the palm of your hand. When dry, you may wish to lightly sand it with fine (220) sandpaper before applying the oil prime.

At this point, you'd be better off to wash the glue you've applied from the canvas (that can only improve things) and start over, so as not to have "overdone" the glue application. Hope this helps.

Thanks so much, Richard. I put the canvas under a stream of water and used a small scrub brush to remove as much glue as possible. I plan to let it sit awhile to soak the glue and repeat the process. How will I know when I have gotten enough off? I would imagine that the glue is inside the fibers and somewhat resistant.

Mary, if you use warm water, a couple of thorough washings should pretty well eliminate the glue. Really no way to tell if all the glue has been washed out, unless the canvas feels tacky when damp-dry.

Thanks Richard, You are a life saver.

Some but not all RSG is rotted and smells bad - no matter the brand. It happens.

Fortunately, you do not need it anymore. Modern acrylic gesso can be applied directly to your canvas fibers - either cotton or linen. As long as you seal the fibers so the oil paint does not touch the fibers, you're good to go.

It is better to apply several thin coats of gesso than one thick one. Sand between coats.

Historical note: Some painters used RSG (water soluble) to seal the surface of the canvas - and then painted directly on top of the RSG. The color of the RSG and the canvas surface was used as the imprimatura.