|
Advantages and disadvantages:
Traditional rabbit skin glue size and oil primer -- The rabbit skin glue is hygroscopic. In simple terms, it tends to absorb humidity, which can swell and shrink the canvas in tiny amounts which, over a LONG time, MAY cause cracking. This is still up for debate as it could also be the result of poorly applied grounds, or misuse of oil paint application.
On the positive side, RSG has a SIGNIFICANTLY improved tightening effect on the canvas. There is nothing quite like painting on a RSG sized linen canvas that is tight as a drum. Additionally, RSG is a TRUE size, whereas Acrylic gesso and even PVA is NOT a real size. A size will be absorbed by the canvas fibers (and/or wood) and will provide a real inside-out protection from oil acids. The greater bloom of the size means the spaced between the fibers are fully sealed in a properly sized canvas. If you DO size with RSG, remember two things: 1) You a OIL ground to prime the canvas. Do NOT follow up an RSG size with acrylic gesso, and 2) RSG sizing is for OIL paintings only.
Acrylic Gesso -- The good? It is cheap and easy. It doesn't require heating or mixing. It does a reasonably good job of protecting the fibers from the linoleic acid in the oil paint which will rot your canvas. However, since acrylic does create a polymer barrier between the fibers and the oil, a size is not absolutely needed, though you can usually still benefit from a PVA size. The bad? Acrylic gesso is NOT a size. It doesn't penetrate the plant fibers and creates an imperfect (but still good enough for most uses) barrier between the canvas and the oil. Worse, it is acrylic and is unacceptable to degradation due to heat and, despite what people might claim, is ALSO hygroscopic (though less so than RSG). While Acrylic can be used under oil (polymerized linseed oil is fairly sticky and generally 'glues' itself quite well to all but the most glossy, impermeable surfaces) doesn't mean that is SHOULD be. Acrylic and linseed oil are two VERY VERY different beasts. The behave differently and are affected differently by atmospheric effects. For so many reasons that I do not have time to detail, you should NEVER paint oil directly over acrylic paint. Acrylic SEALS itself and doesn't allow the oil to penetrate the under-painting. The oil just sits on the top and dries as a weakly bonded film. Over time, it will almost certainly flake off. That said, Acrylic gesso is NOT acrylic paint. The A-Gesso avoids the full barrier issue by containing calcium carbonate and/or calcium silicate (over other calcium compounds) making the A-gesso lightly absorbent. This is a good thing for the oil -- but bad for the canvas as the A-gesso draws into itself small amounts of oil and MAY allow that oil to come into contact with the canvas fibers. Additionally, since the A-gesso is absorbent, it too can absorb humidity that could lead to cracking, especially in poorly stretched canvases (as premade canvases often are), of when using brittle paints (Ivory black, Zinc white, the lower quality cadmiums, etc.) Additionally, the premade canvas are ALWAYS ALWAYS ALWAYS under primed. You've all seen canvases that brag about being double or triple primed. GREAT... almost half way there! A properly primed canvas will be primed 5 to 7 times for a good protective film. Worse still, premade canvases are SPRAY primed which doesn't force the A-Gesso into and in between the fibers of the canvas. Prepared canvases are, imho, ALWAYS crap. This is the store preparation, mass market canvases (even the highest quality 'professional' quality canvases). I know there are a couple merchants and services out there that will provide a hand prepared canvas or panel and those MAY be done to the highest of standards -- but you get what you pay for, and pay for what you get.
For my buck, RSG size and an oil ground on quality (linen preferred) canvas is the way to go. Still, it takes some practice to learn how to properly size and prime a canvas, panel or paper.
Truth is, I don't use stretched canvas all that often. As I prefer a traditionally prepared panel. It has almost all the benefits of canvas (except the lighter weight) and almost none of the problems (with cracking, susceptibility to humidity, limitation of ground materials, etc.)
To create a traditional panel, you'll need, obviously, a wood panel of the appropriate dimensions. Preferable, you want single cut of radial cut hardwood, though you can get by on a properly biscuit and/or finger jointed glue-up panel. Again, radial cuts are preferred. If you want to save a bit of money, or do not have access to good wood or shop tools to plane, joint, and glue wood, you can use MDF/HDF, hardboard/Masonite, or even plywood. Just be aware that and composite wood may contain adhesives and chemicals that can out-gas that damage you painting.
Once you have you wood, I strongly urge you to cradle the panel (that is, strips of wood support around the edge of the panel) and if fairly good in size, consider cross supports. Supports add cost, weight, and are sometime difficult to properly clamp down when the wood glue is drying, so I'd only use them is your panel to very large.
One you have you panel ready and cradled (don't use staples, nails, or other fasteners -- wood glue is all you need and if applied property, is stronger than the wood itself).
When you have you panel, time to get it ready. Since you read on the directions that RSG should be soaked overnight, you were smart enough to prepare your RSG last night, or at least several hours ago.
Heat up your RSG in a double boiler to it is all melted and somewhat thickened watery solution. Do not boil RSG ever. Boiling destroys it.
Apply a thin coat of RSG to the panel. After about an hour, the first coat should look somewhat wet still, but should be reasonably dry to the touch. You can apply a second coat of this size to the wood. If you did not cradle your panel, you may start to see why I suggested the added support. RSG, once soaked into the wood, can warp it as it dries. If you do not notice it yet, you almost certainly would by tomorrow when it is fully dry. You can limit this by sizing the back side sufficiently as well.
Now, with two coats of RSG size down on the panel and when dry enough that it should not longer be wet to the touch, or slimy in any way, it is time to apply a fiber layer. I tend to use canvas because I always have it around, but you can use another COURSE fabric such as muslin. Cut a piece of material so it is an inch or two large than you panel. Depending on the dimensions, you cansoak the material in the RSG or paint it on heavily, soaking it though and through. The fibers should be fully wetted. Not, take that wet, sticky material, and cover the front of the panel. Spread it out evenly, making sure there are not wrinkles or bubbles. Some tiny bumps or imperfect textures don't matter too much.
At this point, I've had just about enough of sizing and gluing, and set the panel and the canvas facade out to dry fully -- usually ready the next day.
The next day I trim the canvas flush to the panel front. I do NOT wrap the material down the sides or around the edges like normal stretched canvas. This canvas is glued to the board and short of conservation solvents, is not coming off. Just go ahead and trim tot he edge, cleanly. Put some more RSG in the double boiler to liquefy. While waiting for it to be ready, inspect the panel to make sure the canvas is glued down 100% on every square millimeter of panel surface. If any corners are coming up, I'm take care to apply more glue to those corners to glue them down again.
Once the glue is ready, apply another coat of RSG to the canvas panel front. If you soaked the material well when you glue it on, you probably only need to size the material with one more coat. Once that coat is dry enough to not be slimy or overly tacky, it's time for the next step (my favorite). Make gesso. NOT acrylic gesso as we were talking about previously (which is not gesso at all). Gesso is made by mixing RSG with slaked plaster of paris, gypsum, whiting or marble powder. Shoot for roughly 3:1 RSG:Marble, though your exact proper mix will be learned with time and experience. Your Gesso will look and feel a bit like heavy cream.
We are going to be adding a BUNCH of coats of this gesso to the panel -- 7 or 9 perhaps, though I've added as much as 15 if I'm sanding heavily. Apply a coat in a single direction only and additional coats should be applied perpendicular to the previous. Every 3 or 4 coats, it is often a fairly good idea to sand the DRY gesso panels with a very fine grit sandpaper (320+). As you build up the gesso, you'll cover up the material completely, as well as any defects in the panel. When I think I'm getting down to the last 2 or 3 layers of gesso, I'll add a dry pigment to the gesso. Titanium or lead white (use a mask any time you are dealing with powdered pigment, but failure to do so with lead can eventually lead to your death.) creates a bright white ground, but I tend to use colored grounds, preferring Raw or Burnt Umber (defending on whether I want a yellow/green brown tone or a red/brown tone.
Paint those layers on -- this time, try to sand between each DRY layer. When you are done, you can finish the gesso panel off with a fine steel wool if your color is not reactive to irons. The end product to a flawless, amasing surface that is a true joy to paint on. It is suitable for egg tempera, casein tempra, gouache, watercolor, silverpoint, pastel/charcoal. However it is too absorbent for oil just yet, so the last thing you want to do to apply on more clean layer of RSG size WITHOUT any calcium. This will seal off the ground to a large degree and will keep the gesso from drinking up your oil.
Traditional gesso panels are VERY stable and long lasting. When done properly, and when you paint with quality paints, being careful to follow rules from drying times and fat contents, your painting will last for many, many hundreds of years.
Is the prep a pain in the butt? Absolutely! But, if you enjoy material, especially those of the Old Masters half as much as I do, it can really be fun. And, though I spoke as if doing a single panel, when I do this process, I usually do it on perhaps two dozen panels at a time, so I'm not wasting too much time and glue between coats. I usually have 5 or 6 individual quarts of glue gelled and ready to be heated. So, unless I'm prepping panels for other people (I sell my panels to fellow local artists who love the panels but do not wish to go through the preparation process), two dozen panels, will usually last me personally a few months, though I admit that I do tend to have to prep panels every couple weeks, due to my sales.
Ok, it is 2:36am and I need to go to bed. I'm reasonable sure that my exhaustion has made the above and unreadable mess.
|
