Preparing a canvas for oil (or acrylic) painting

Benedito_tela
I got a little help from my studio cat while making this canvas.

Learning how to make your own canvas is really useful, because often store bought canvas don’t seem to be well prepared for painting. Sometimes they have a sparse coat of gesso, or the fabric is too thin. This can compromise the visual final result, or the painting conservation over time. Most importantly: oil paint shouldn’t be applied directly on the fabric, because eventually it will damage the fibers.

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Materials needed to prepare a canvas: fabric (usually cotton or linen), a brush, PVA glue, acrylic gesso, a sandpaper. Besides these, a wooden frame and a stapler, if you want to stretch the fabric before to prepare it.

The fabric may be prepared after it was stretched over a wood frame (what I prefer and recommend) or no. If you are using a wood frame, it’s advisable that the laths have a rounded edge, so the frame wouldn’t rip the cloth where it folds (see in the picture). I’m using here an already built wooden frame, from a canvas previously used for a study. In case I make the frame, I prefer to ask a carpenter to saw the wood, so I’m sure it’s cut in perfectly 45 degrees angle.

canvas_wood-frame
Red arrow: rounded edge (for the side in touch with the fabric); blue arrow: sharp edge (canvas backside)

There are a couple of ways to prepare the fabric. This one, I think is the most practical and useful I’ve learned.

First of all, one needs to choose the fabric. The most used are linen and cotton. There are some others, like polyester and jute. Linen has been used for a longer time. It’s quite more expensive than cotton, and stiffer to stretch. Usually, it offers a delicate woof. Some people argue that linen lasts longer than cotton, because cotton absorbs more moisture. But the better durability of linen is not well proven. From my experience, linen is also somewhat harder to find.

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Cut the fabric at least one inch larger than the frame, to fold the excess in each side.

The fabric texture may be coarse  or more regular and even. This is a matter of personal preference, and it depends greatly upon the final result one wants in the painting. Usually, a delicate surface is desired for realistic paintings. Also, differents textures present differents “feels” for the brushwork. Still talking about the fabric: it’s recommended that the fabric be raw, not dyed. The raw cloth usually has a beige ir brownish tone. Fabrics may be composed by a hundred percent type of fiber, or they may have synthetic fibers on it – for example, 20% polyester and 80% cotton; but it’s not known for sure if this is good, in terms of durability (distinct fibers may behave in an unequal way under climate variations).

tela_gramp
A heavy stapler is needed to fasten the fabric to the frame

A heavy stapler is needed to fasten the fabric to the frame. It’s better to place the first staple of each side in the middle. After fastening one side, do the same with the opposite side.

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A stretched fabric of raw cotton, over the frame.

SIZING – If the cloth is stretched on a frame, ensure that it’s not too tight, because, after the glue is applied, the fabric shrinks, so this will warp the wood.

This is the step when we fill the gaps in the fabric. The simpler way to do this is by applying a layer of PVA (polyvinyl acetate) glue. This process isolates the fabric from the paint, thus protecting it. If the canvas wasn’t well prepared at this stage, over time the fibers will rot, and also stains of oil may emerge on the back of the canvas.

This glue layer also acts by decreasing the flexibility of the cloth, locking its threads, and avoiding them to expand or contract (what happens due to moisture  in the surroundings).

In the old days (and some people still do it) rabbit skin glue was used for sizing. But, besides PVA glue being more convenient, I prefer to use a non-animal origin product. There are also some concerns that rabbit skin glue has conservation issues.

There are other products that can be used for sizing, like some types of acrylic foundations (be sure that the label specifies this purpose).

You may need to add a bit of water to the PVA glue, so it will be easier to spread. But don’t dilute the glue too much, or it will lose its function.

Apply the glue generously with a large brush, until the fabric is soaked in glue. Don’t forget to apply it on the sides. I like to apply the glue also on the back of the canvas, the improve the protection from moisture.

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Applying PVA glue. After the glue is dry, it will be transparent.

I’m showing this process in which glue is applied, and, after this,, the gesso comes. But some people use a single mixture that serves both for sizing and gessoing, at the same time. This mixture usually is made up with PVA glue and latex paint. But there is a risk that wall paint won’t perform well in terms of lighfastness.

PVa glue dries fast, but it’s safer to wait for some hours before jumping to the next step, so we’ll be sure that it’s really dry.

PRIMING – It consists in applying layers of “gesso”, after sizing. The “gesso” that we use today (acrylic gesso) is actually not authentic gesso. Before acrylic gesso was available, a mixture of rabbit skin glue (or another binder), chalk and white pigment was used for priming. Over time, emulsions of acrylic resins have inherited the name “gesso”, as they substitute its function. Usually, the acrylic gesso that we find readily to use at stores are suitable to prepare the canvas for both oil and acrylic paints (but specific oil based primers shouldn’t be used to prepare a canvas for acrylic painting).

The priming creates a coat ready to accept the paint. It also changes the absorbency of the canvas, its texture and color (if you add a tone to the gesso). Most importantly, the priming improves oil painting adherence to the surface.

The gesso should be applied in layers, at least two of them. A more even surface may be obtained with more layers. The acrylic gesso may be thinned with up to 15% water. The first layer consumes more gesso. As the surface becomes less absorbent, the next layers consume gradually less gesso. I spent about 300 to 350 mL of acrylic gesso for printing 10 to 12 square feet of canvas (I applied 3 coats of gesso).

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Applying the first coat of gesso

Use a large brush or a paint roller to apply the gesso, and don’t forget the sides of the canvas. A brush for wall painting tends to drop a few bristles, specially at the beginning, so you may need a tweezer to remove them, and any other lint, while the gesso is still wet. As this process quickly wear out the brush, it’s not worth to use a fancy (and quite more expensive) oil painting brush.

The acrylic gesso dries fast, what can be checked touching the surface (it’s cold if it’s not dry yet). Usually, in up two hours it’s dry, but this may vary with the weather. The second layer should be applied in a perpendicular direction of the first, and so on.

gessoed_canvas
A canvas after the printing with 3 coats of gesso

After the last coat is dry, the canvas should be scuffed. A sandpaper of 320, or with a thinner grit, is fine to sand the canvas. The grit depends upon the final result one wants in the surface. After this, your canvas is ready.

lixandotela
Scuffing the surface, after the last gesso coat is dry, with a 320 grid sandpaper.
texture_canvas
Finished cotton canvas, ready for painting
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