HOW TO STRETCH A CANVAS

I am hoping at some point to get to making a short video demonstrating how I stretch a canvas but for the moment here is a step by step guide. There are various methods that artists use but this is the way that I am currently using to stretch mine. It is based on advice from painting conservators whom, having experienced many many times the obvious indication of cracking patterns in the corners of paintings from overstretching of the canvas, advise this method of stretching. Many thanks to James Bernstein and Golden paints for some of the photo illustrations.

It is surprising how quickly a painting on canvas will deteriorate because of incorrect suspension. There is a direct correlation between proper canvas preparation and painting longevity. For paintings on canvas, the suspension/tension of the fabric is of utmost importance. A well-stretched canvas is a well-suspended one. If well suspended, well painted and well cared for, a painting may go quite some time before intervention is needed by some future conservator.

If canvas suspension is not uniform throughout, variations in tension across the painting result. Extremes in canvas pull (overly tight or overly loose) and planar distortions (sags, puckers or draws) will have adverse effects over time. Strain is transferred to the sizing, ground, paint and varnish applied on top of the fabric. These forces lead to cracking, lifting, buckling and flaking of the paint and ground layers.

This way of stretching does take longer but it is a better safeguard against future problems. If you are going to invest a whole lot of time into your paintings, its best to get it right at the very beginning.


typical corner cracking showing too much tension from stretching

 

Select a workspace with plenty of light and space to maneuver. Prepare a clean large worktable, sawhorses or floor area. If using the floor, be sure to lay down a clean piece of polyethylene sheeting or paper to prevent transfer of dirt from the floor. For successful stretching, the studio space should be closed off sufficiently so that some semblance of a constant, moderate environment is maintained throughout the procedure. Stretching will be much easier if the room is on the warm and humid side as materials will be far less flexible and plastic if the room is too cold and dry.

Make either a braced (fixed) or stretcher bar frame, ensuring the corners are 90º square. If using stretcher bars - do not staple them across the joins. There is no point ot investing in the cost of purpose-made stretchers that will not be able to move outwards later to increase tighness. You might as well make a fixed frame. I have seen it just too many times. On larger stretchers you can attach metal angles with screws to the corners of stretcher bars (on the back!!) temporarily to keep it from moving out of square and remove them when you are getting close to the corners to finish the stretching/tacking.

Handle pre-primed canvas carefully. Though generally durable, it is very easy to put permanent crimps or breaks in the continuous priming if its bent. Make sure the elevated shoulders of the stretcher bars or quarter rounds of the brace are facing the back of the canvas. Line up the stretcher as best as possible parallel to the weave on the back of the canvas and faintly mark the fabric, tracing the extreme edges and corner of the stretcher with a pencil. Don’t forget to also mark the 3 to 4” beyond the stretcher as well.

Cut the canvas piece with enough extra allowed to cover the sides and back of the stretcher at least halfway, usually 3-4inches bigger than the stretchers on all sides. Do not be stingy, maxing out the fabric and leaving only a 1⁄2” beyond the stretcher. This will make stretching difficult.This is also important as it will facilitate the possibility of later re-lining of the canvas in the future. Well, you never know!

Using push pins ( You might have to lightly tap them in with your canvas pliers to hold the fabric sufficiently) Start in the corners and work towards the centers, using the pliers to gradually coax and stretch the fabric. Its important to avoid fast, forceful movements and stretchin the canvas too tightly as these could break the priming or threads (its easily done - think of the process as a mindful meditation). Pin two pins in each of the corners first, making sure the threads of the canvas are aligned properly, parallel with the stretcher bars.

Move towards the centers until completed. Alternate opposing sides, turning and stretching as you proceed. When inserting pushpins, tilt them upward slightly to counteract the pull of the canvas so they won’t pop out. Turning the pins while pushing helps to drive them into the wood but you can tap them lightly with the pliers if necessary, especially on hard old stretchers.Do not set in the pins too deeply- this will make removal difficult and will limit easy readjustments.

When a canvas is stretched and pinned starting from the corners, the unset center portion is unrestricted. As stretching continues, the center is gradually pulled up, but with no undue, irregular tension. I am sure you may be worrying, “what if I end up with a big welt of fabric left over in the middle with nowhere to go?” Please do not worry. This simply will not happen.


If you can be patient and wait (which I rarely am!), set aside the stretched canvas pinned on its stretcher for a day or two before completing with staples or tacks. With climatic shifts and the passage of time, the canvas will relax and settle onto the stretcher, giving a true indication of how even or not the stretching is. If puckers, draws or slackness appear, the pins can be removed from those locations and the canvas re-stretched as needed. When the desired canvas suspension is achieved, the canvas may be placed face down against a clean wall or floor. If the latter, lay clean paper, glassine or polyethylene sheeting on the floor, to be sure that grit or dirt does not become embedded in the priming ground.

I personally prefer to wrap the canvas completely around to the rear of the stretcher, maybe halfway across the flat part and tack with staples to the stretcher reverse. This also keeps most of the tacking well away from the frontal image plane, especially if you are not going to use a frame. Do not remove or trim extra fabric. Remember to leave generous canvas margins to provide work edges for when the canvas needs re-streching or conservation in the furture. Never cut away fabric at the corners. Finish the corners, neatly folding and tucking the fabric under and to the back. Some artists use two folds; others choose to gather the canvas in a single fold.

The pins should not be removed from the stretcher edges until the canvas is completely stapled or tacked. While the pushpins are holding the front of the canvas under tension, the fabric should still be pulled with finger grip or pliers just prior to setting each staple on the reverse. Its best for pins and staples to be evenly placed at 1-1/4 - 1-1/5 inch intervals. The 3-inch to 6-inch space between staples or tacks that is often seen on modern paintings is simply inadequate. This results in uneven canvas tension, undue slack and cusping (a scallop-like appearance like Viennese curtains) of the canvas.

Some like to use a band of fabric between the staples and the canvas to reduce staple crushing and cutting. Cotton strapping, linen tape, polypropylene strapping, etc.) as cushioning between the staples and the canvas. This system is particularly suited to paintings that require repeated unstretching and re-stretching.


Stretching Pliers Design
Fingers and hands are unable to stretch canvas with the strength that well designed stretcher pliers an althoughh there is a danger of overstretching with pliers. Canvas Pliers come in a variety of types but examples available in art stores are often limited and is worth researching on the internet before buying.

The most commonly and cheaply available pliers are ones with small rectangular jaws with interlocking “s”- wave profiles (like crinkle-cut chips). This design increases surface area of contact and guarantees a powerful lock against slippage. Unfortunately, the sharp jaws often also guarantee over- tightening, crushing and weakening of the ground and fabric, sometimes to the point of tearing the fabric.

My preference is for pliers with relatively flat-faced jaws; sometimes the face surface is cast or tooled with a mild textural pattern to insure against slippage. The jaws should be good-sized in surface area and of decent quality and leverage to grip well. My favourites are the cast steel Holbein pliers below. Although much more expensive, after going through 3 pairs of Frederix ones due to metal fatigue, I bit the bullet and bought the ones on the lower pictue left and they are still perfect after a decade.

Most pliers have a central heel protruding just below the jaws. This heel serves as the leverage fulcrum. It is braced against the stretcher wood, the pliers are rotated (pushed forward and downward), and the fabric is pulled tight. Plier handles may be set at different angles, depending upon if the pliers are designed for face-up, sideways or face-down stretching. It is helpful to have pliers for different jobs; a super-sized canvas requires pliers different from those designed for smaller canvases.


Staples and Tacks
There are arguments pro and con for both heavy duty and lightweight staples. I try to select those that are suited to the demands of the project at hand.

• Heavy-duty staples have a nice flat wire profile that grips fabrics nicely. It does not usually cut across the long flat face, but it makes good-sized holes at the two points of staple entry.

• Lightweight staples of fine wire size make very fine entry holes, but have the potential to cut into the fabric if driven too far.

Any staple, really, has the potential to crush the fabric if the wood is very soft and/or the staple gun delivers with too much power. Whether manual, electric or air-compressor driven, a staple gun that offers tacking power adjustment is best. Also, it is not necessary to go overboard with the staple length. A 5/16 or 3/8 inch long staple is plenty deep. A 3/4 inch long staple is overkill and anyone removing these deep staples will be cursing whomever did the stapling.

Always take great care when removing staples. Use a tapering, tongue-shaped staple remover tool, gripping it firmly and gradually working the tongue under the staple, prying upwards. Never pull upward on the canvas itself to remove staples - it will tear the fabric. And never rush staple removal or allow a tool to slip. Shortcuts or accidents result in punctures or tears to the all-important tacking margins.

See my bulletin board listing for the stapler that I recommend: www.geoffreylaurence.com/bulletin.html#stapler

If you are using stretcher bars rather than a braced frame you can tap in lightly the wooden keys that are supplied with the stretcher bars for later use into the slits inside the corners. They should be inserted with the shorter diagonal AGAINST the flat of the stretcher, not the other way round - its counter intuitive I know but it prevents the wood from splitting when you hammer them in.

Some of the canvas stretching illustrations are courtesy of James Bernstein and Golden paints.
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