Studio Craft: Troubleshooting Canvas Stretching

Ask the Expert: “I recently started stretching my own canvases. No matter what I try, I always seem to get an uneven, wavy pattern. I have puckers around the edges, too. I thought about using a spray on the back, and a friend said I should use the wooden wedges that come with the stretchers. Will this fix it?

A:It's important to address wrinkles and puckers because a flat, dimensionally stable surface is essential for long-term durability of the painting. Which approach to take depends on the severity of the wrinkles.

The source of weave irregularities is usually stretching technique or uneven shrinkage with a strong sizing. Certain types of linen fabric can develop an undesirable wavy pattern when sized with Rabbit Skin Glue. Canvas that's incompatible with RSG is usually labelled "for use with synthetic size only". There are only a few kinds of canvas that are affected by RSG, however; most types can be glue-sized with no problem.

Stretching on the bias

Most of the time, weave distortion is caused by how the fabric is stretched. The technique most artists learn for stretching canvas involves starting in the center and pulling directly against warp and weft yarns, working out toward the corners. A skilled craftsman can normally achieve good results with this method, but canvas weight and type can affect quality of the finished product.

Pulling directly across the stretcher frame can result in uneven tension from spot to spot. It can be challenging to pull with the same amount of force at the corners as in the middle of the bars, even with canvas pliers. An alternate method-stretching diagonally on the bias- helps evenly distribute tension by displacing the entire network of warp and weft, avoiding tight spots along the span of each stretcher.

Spot Adjustment
One defect that can be caused by poor execution of the standard stretching method is scallop-shaped puckers at the tack points. Isolated puckers can be corrected by removing single staples, adjusting tension and re-tacking. This remedy is also effective for wrinkles in stiff, primed fabric.

Slight irregularities in stretching can be smoothed out by "keying out" the canvas chassis. Insert 2 keys at each stretcher joint and insert gently by tapping with a hammer, taking care to protect fabric from accidental hammer strikes.

Keying out is a good way to fix a loose canvas, but it may not be enough to fix large wrinkles. Also, if the artwork is scaled to an existing frame or architectural niche, using keys may not be an option since the frame may not fit the rabbet or niche after expansion.

Tightening Spray
Canvas tightening spray is a fast-drying liquid that induces shrinkage to reverse dimples and slack spots in stretched fabric. Tightening spray also includes sizing to make this effect permanent.

Tightening spray can be very effective at reversing dimples from pressure, and it can be used for small, isolated wrinkles. More extensive wrinkles may be reduced by spraying, but they may reappear after the canvas relaxes; if this is the case, a more thorough approach is needed.

When wrinkles, puckers or ripples are extensive, the best approach may be to remove canvas from the stretchers and try again.

Canvas that has rippled after preparation with RSG can be removed from the stretchers and laundered to remove the sizing. Fabric should be line-dried after washing. Never wash canvas that has been synthetic-sized, primed or painted. Make sure canvas is completely dry before stretching- canvas fibers are at their longest when dry, so canvas stretched damp will tend to become slack.

When re-stretching, insert staples diagonally in a tight grouping parallel to one another to ensure broad coverage along each side. Correct any distortions right away, before sizing.

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