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Old 02-19-2007, 11:50 AM   #1
Thomasin Dewhurst Thomasin Dewhurst is offline
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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?
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Old 02-19-2007, 11:55 AM   #2
Ilaria Rosselli Del Turco Ilaria Rosselli Del Turco is offline
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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 :-)
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Old 02-19-2007, 01:03 PM   #3
Jean Kelly Jean Kelly is offline
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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!)
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Old 02-19-2007, 03:20 PM   #4
Karine Monaco Karine Monaco is offline
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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 ?

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Old 02-19-2007, 03:40 PM   #5
Richard Bingham Richard Bingham is offline
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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.
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Old 02-19-2007, 04:57 PM   #6
Richard Bingham Richard Bingham is offline
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Quote:
Originally Posted by Karine Monaco
. . . Has anyone tried modern binders that would not cause any problem of slacking? . . . a big canvas . . . started to slack when I was working on it . . . product named RSG . . . was not true RSG . . . Karine
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.
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Old 02-19-2007, 05:13 PM   #7
Carlos Ygoa Carlos Ygoa is offline
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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
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Old 02-20-2007, 11:18 PM   #8
Thomasin Dewhurst Thomasin Dewhurst is offline
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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?
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Old 02-21-2007, 01:05 PM   #9
Claudemir Bonfim Claudemir Bonfim is offline
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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.
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Old 02-21-2007, 01:30 PM   #10
Richard Bingham Richard Bingham is offline
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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.
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