Polyester

 

I've started painting on polyester cloth instead of canvas. In many ways it's probably far better than linen.

It's immensely strong and very inelastic; it doesn't expand and contract over time as much as natural fibres can. Even if it's very thin, you can use it on a large scale, as long as you have a really solid, reinforced stretcher frame. Unlike natural fibres, it can't be damaged by the acid in linseed oil. Also, it's sometimes cheaper even than flimsy 9oz crap cotton canvas at an art supply store. If Dow Chemicals had existed in 16th Century Venice instead of a large sailmaking industry, Titian would have used polyester, and I bet many of his paintings would never have had to be relined.

I used to use something called polyester tableing material (presumably somebody uses it for tablecloths?). It was fairly thin, maybe a bit thicker than Oxford cloth, and could be used for a canvas up to 66" in one direction, with no limitation in the other. It was excellent, but then the manufacturer started stainproofing it, rendering it totally unabsorbent. The stuff I use now is much thicker, more like the canvas generally used for painting.

To determine whether any given cloth is suitable, you should look for certain characterisics. It has to be pure polyester, not mixed with anything else. Colour probably doesn't matter, but it has to have a smooth enough texture to be usable for painting. It must have no discernable stretch, and the fibres should be really difficult to break. I bring a tiny dropper bottle of water, and surreptitiously wet the cloth to see whether the water sinks in easily, or beads up and rolls off. Whatever you use, the best place to get it is probably at an ordinary large fabric store, such as Fabric Land. This is a co-op type store; if you get a membership, be prepared to recieve embarrassing and emasculating mail, advertising sales on things like lace and sequins.
Important note on buying polyester at Fabric Land: Always bring an old plastic bag from House of Tools or somewhere. When you leave the store after buying the polyester, immediately place the Fabric Land bag inside the other bag to conceal the fact that you've been shopping there.
If you must have the texture of linen or cotton canvas, then you might not like the stuff I use. But I make it look almost like a panel by scraping on four very thin layers of lead primer over rabbit glue. You may or may not be able to find some other kind of polyester with a thickness and weave a bit more like cotton duck or something.

Polyester has to be stretched very differently from other canvas, because it hardly stretches at all. If polyester cloth is stretched unevenly, rabbit glue won't even out wrinkles and flaws in the surface, because it doesn't shrink very much when sized. I worked out a method which is very effective, though more complicated than the standard tack-in-the-middle, diamond-shaped-wrinkle procedure. But it results in a very evenly tensioned, perfectly aligned canvas, and would probably be a good way to stretch any other kind of canvas as well.

 

How to Stretch Polyester

You will need:
                -Polyester canvas
                -A heavy stretcher frame
                -Flat angle irons (optional)
                -A pencil
                -A thick felt marker
                -A yard stick or tape measure
                -Stretcher pliers
                -A heavy staple gun with 3/8" staples
                -A flat screwdriver
                -About a million plastic push-pins

Except for very small canvases, maybe 16" being the maximum dimension, polyester has to be stretched on a heavy stretcher, the kind that's about 1 1/2" deep. It should be totally flat, with robust corners.

The cloth should be large enough to wrap around the back of the frame at least 1" on all sides, so for a 1 1/2' deep stretcher frame, there should be 2 1/2" of overlap on each side. Cut the piece of cloth to the right dimensions, and then make sure all the size is gone by putting it through a washing machine. When it's finished, don't dry it, iron it while it's wet. The wrinkles should come out fairly easily, but don't worry if you can still see faint traces of them when you're finished. Hang the cloth over a dowel or something, in such a way that it won't get wrinkled again while it finishes drying.

The following instructions may look complicated, but the process is simpler than it seems. Just follow the steps and don't panic. Once you grasp the principles involved you will realize that it isn't horribly complicated, but that it is horribly tedious.

 

Step 1

Assemble the stretcher, and square it by measuring the diagonals. They should be the same to within less than 1/8". If you want, fix the corners temporarily by attaching the angle irons to the back of the frame. Don't butt them up to the corners--make sure there is still exposed wood for the staples to go into.

 

Step 2

If you were stretching cotton or linen, you would want to coat the frame with a thin coat of acrylic medium or white glue, to prevent acid from the wood leaching into the fabric. But you're using polyester, and all you really need to do is rub a very thin layer of vaseline onto the frame, so that any rabbit glue soaking through the cloth will not glue them together.

 

Step 3

On the inner edge of the back of the frame, mark off every inch on each side with the felt marker. Each one of these marks will correspond to a push pin, and later to a staple which will replace it.

 

Step 4

Clear a space on the floor, and make sure it's not grubby, because you then lay the cloth down on it. If the canvas isn't big, you can use a table instead, assuming you have a table that isn't completely covered in junk. Position the stretcher frame as symmetrically as possible on the cloth, bevel side down.



The frame on top of the cloth

 

Step 5

Using a push-pin, pin the cloth in the middle of one side. Go to the opposite side, pull it medium tight with only your fingers, and pin it as well. Pin the other two sides in the same way. You have now approximately detemined the eventual tension of the cloth.



Mark along the edge

 

Now make a small pencil mark along the back outer edge just above one of the pins. Do the same for the other three sides.

 

Step 6

Unpin the cloth and put aside the stretcher. Extend each mark all the way along its edge. The weave of the cloth will probably have a direction to it--on one axis you can simply run the pencil along the weave, while on the other axis you should measure the distance of the mark from the edge, make other marks the same distance in, and then join them with a yardstick. If you can't follow that last sentence, just look at the pictures.



Measure from edge, then make other
marks the same distance in




The marks extended into lines

 

Step 7

Now turn the cloth so that the side with the pencil marks is face down on the floor. Put the frame back on it, and pin the corners as shown, making sure the lines you drew correspond to the proper edges. You will need the stretcher pliers for this. Make sure you are pinning into the sides and not into the back of the frame.



Pinning the corners

 

Get it? Matching the line to the edge of the frame every time you put in a pin will ensure that the tension is even across the face of the canvas, while pinning the corners first will ensure that the tension is even along the edges.

 

Step 8

Start pinning one side. Pin in the middle first, pulling the cloth to align the the pencil line to the edge, as you will for every pin. Then put in another pin at an inch mark about half way between the center and corner pins. Keep putting in pins at inch marks roughly half way between other pins; don't just start at one end and work your way to the other.










Putting in push pins by halves (approximately)

 

Sometimes you'll want to stand the frame/canvas up on edge for this, but be careful. It will be standing on push pins; if you're not careful you can bend or break them, and they can easily pop out. They can also make the whole thing skate around on the floor.

Keep putting in pins until you have entirely filled in all four sides with pins at 1" intervals. This will be very boring.

 

Step 9

Adjust the pencil lines anywhere they might be out of alignment--remove the pin, adjust the tension, and replace the pin. You can do this to a whole side if you have stretched it too tight.

 

Step 10

Put the canvas back on the floor, and put in a staple for each pin/inch. Grasp the edge of the canvas with your fingers, and pull as hard as possible as you put the staple into the back of the canvas, near the edge. You pull this hard because for each pin on the side that you replace with a staple on the back, you lose a bit of tension. Put in a staple for every single push pin, except for two at each end of the top and the bottom of the canvas, where you will fold in the corners.

When you get to stapling down the corners, make sure the folds are pointing outwards, not inwards along the side of the canvas. Again, look at the pictures if that's confusing. Folding them this way is supposed to make the corners more resistant to wear and tear--I don't see how, but I do it anyway, partly because it looks better. Pull them tight with the pliers and staple them down.


Wrong way

Right way

 

Notice how the pencil line is about 1/8th" away from the edge, rather than precisely aligned to it. That's because I stretched it a little too tightly in that direction at the beginning, before I made the little pencil marks. When this happens, you usually have to unpin one side and redo it--that's why you start with push pins instead of staples. The important thing is that the pencil line ends up parallel with the edge.

Remove all the push pins and the angle irons, and the canvas is finished. Now size it with rabbit glue and prime it with lead primer.

 

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Copyright © 2013 by Harry Steen