Flexible Supports
Stretching the Canvas

Equipment

Hammer
Screwdriver
Ruler
Try Square. Carpenter's 8-in. try square.
Pliers. Artist's canvas-stretching pliers or upholsterer's pliers.

Materials

Canvas. Artist-quality unprimed canvas that is free of starch or stiffener. If there is suspicion that such material exists in the canvas, rinse it out well in clear warm water. Allow canvas to dry thoroughly. As an alternative, ready-primed artist's canvas, single- or double-primed, can be used.

Chassis. Four wooden stretcher strips. Examine them carefully at time of purchase, and be sure that they are not warped.

Tacks. No. 6 upholsterer's tacks [carpet tacks].

[p. 97]

2. Cut the fabric from the roll. Mark the piece 3" longer and 3" wider than the frame. That is, if the stretchers are 24" by 30", the canvas should be cut 27" by 33". This allows a 1 1/2" overlap on each side of the frame, which is needed to get a grip on the canvas during the stretching operation.

3. Place the canvas [primed side down, if it is ready-primed canvas] on a smooth surface such as a large table. Put the assembled stretcher frame on top of it in such a way that it is centered and there is an equal amount of excess canvas around each side of the frame. Be sure at this point to line up the weave so that it runs parallel to the sides of the frame.

4. Mark the center of each stretcher strip, using a ruler to determine the center.

5. Bend the excess canvas over the narrow edge of one of the short sides of the frame. Keep the frame flat on the table and tack the canvas to the center of the narrow outside edge, using the center mark as a guide. Do not drive this tack all the way into the wood, but rather drive it only halfway so that it may be easily removed later. Drive a second tack into the same stretcher strip about 3" from the end. Drive a third tack about 3" from the other end. Drive these tacks only partway into the wood, as they too will be replaced. Thus one side of the frame has three tacks in it: one in the center and one at each end.

6. Tack the canvas at the center and ends of the opposite stretcher strip, driving these tacks only partway into the wood . Do the same fog the two remaining sides.

7. Pick up the frame and canvas and stand it on edge. Using a screwdriver, remove the center tack that was driven in first. Pull the canvas tight by hand or with stretching pliers and replace the first tack, driving this and all the following tacks all the way into the stretcher strip. Now remove the corner tacks, tighten the canvas, and tack the corners again. When tightening the canvas, always pull away from the center towards the corner. Do the same with the tacks in the opposite stretcher strip, pulling the canvas tight. Repeat the process with the two remaining sides.

8. Drive a tack on each side of the first tack, about 2" away from it. Pull the canvas tight before putting in tacks. Also pull canvas slightly toward corners to be sure to eliminate folds or wrinkles between tacks.

9. Do the same on the stretcher strip on the opposite side. Be sure each tack is directly opposite the tack it faces so that the tension of the canvas is kept even. Then do the same on the remaining two sides.

10. Continue to put tacks at 2-inch intervals on all sides until the canvas has been secured up to the corners. Remove the original corner tacks.

11. Make a neat fold in each corner and tack it. Be sure the corner tack goes into the heavy part of the joint. Tack or staple the excess canvas down to the back surface of the stretchers.

12. If there are any wrinkles or folds, remove the tacks at that point with a screwdriver, pull the canvas tight to eliminate the fold, and tack it again.

13. Corner wedges or canvas keys are supplied with the stretcher strips. They are driven into slots that are in the inside corners of the frame after the canvas has [p. 98] been stretched to take up any slack that may come about at a future time. If the canvas has been well stretched, they should not be needed in the begining. If used carelessly, they may spread the joints of the stretcher frame so far as to cause the canvas to tear at the corners.

[pp. 98-100.]

Notes [On canvas stretching procedure]
A. Canvas that already has a ground on it must be stretched tight and smooth. Stretching pliers are usually necessary to do a good job easily. On the other hand, raw linen that will be sized and primed after it has been tacked onto the stretcher frame need not be as tightly stretched, and the job can be done by hand, without pliers, since the fabric will usually tighten up considerably by itself when it is glue sized. In fact, if a heavy raw linen is used, trouble may result if the fabric is stretched too tightly, since the contraction may be great enough to break the stretcher joints.

B. The back of the stretcher strips can be marked off at regular 2-inch intervals, starting from the center of the strip. These marks will then serve as an accurate guide for the even placement of tacks. Alternatively some artists use the width of the stretching pliers jaws to gauge the interval between tacks.

C. Heavy-duty staples driven by a stable gun are sometimes substituted for tacks. The advantages would seem to be that each staple has two points of contact, that the gun may be operated with one hand while the other hand is holding the pliers, and that it is a faster, neater, and less expensive operation.

D. Two or three heavy staples or large upholstery tacks, driven across the miter joints of the assembled stretcher frame, will keep the frame from going out of square during the stretching operation. Temporary wooden braces or Masonite [Masonite Corporation] triangles fastened diagonally across each corner will serve the same purpose. These may be quickly made of any odd pieces of scrap wood or Masonite and temporarily nailed to the stretchers. The tacks, staples, or braces are taken off after the canvas has been stretched.

E. If a long canvas, for example 26" by 48", is stretched on unbraced frame, the tension of the canvas may cause the middle of the 48-inch long side to bow inward so noticeably as to be a framing problem. Such canvases should be braced against the tension by putting a cross brace between the centers of the 48-inch stretcher strips. Artists can buy stretchers fitted with cross braces by ordering them from art supply dealers. These braced stretcher frames are made with mortise slots that receive the fitted ends of the cross braces that are furnished with the stretcher strips. The painter can key out the cross brace along with the stretcher strips if the stretcher frame nerds to be expanded. Alternatively the artist can use plain pine stock, about 2 1/2" wide by 1/2" thick, to make the braces in the studio. The stock can be bought in lumberyards. Cut the stock so that it fits snugly between the inside edges of the two longest stretcher strips at their [p. 100] mid-points. Then use two brads at each end of the brace to hold it in place. A better way to hold the home-made cross braces is to use the patented cross-brace brackets [Fredrix. Tara Materials, Inc. ] that are sold for the purpose. These srcure the brace to the stretcher strip and allow the artist to install the braces and then remove or reinstall them at will. The brackets, designed for braces 3/4" by 5/8" thick, are made of plastic and can be bought in art materials stores. Once the canvas has been well stretched and sized, the brace can be removed.

F. If a primed canvas is stretched on a damp, rainy day, it will remain tight in humid weather. If it is stretched on a dry, warm day, it will be apt to loosen to some extent in a humid atmosphere.

[pp. 100-101]