ASK THE EXPERTS

Product Profiles: Canvas Stretchers: An Overview

The familiar wooden canvas stretcher ismore than a simple frame. It's a machinedesigned to apply and maintain tension oncanvas paintings. When assembled, fourstrips form a chassis that provides bothflexibility and rigidity.

How Stretchers Protect Paintings:

Simply put, a tight canvas is a flat canvas,and a flat, stable fabric support reducesstress on the paint film. Achieving a tightstretch initially allows the sizing/priming tostiffen the fabric into a stable plane. As thepainting ages, a good stretcher frameshould facilitate small adjustments intension to maintain flatness.

The Lift

The "Lift" is a proud articulation at the outeredge of the stretcher strip. It maintainsspace between the back of the canvas andthe face of the frame, preventing a ghostimage from developing in the painting.

Some light-duty stretchers have a fairly shallow lift that is the same on both sides,so it doesn't matter which side faces out.Most heavy-duty stretchers, however, have the lift only on one side, so it's important to have the correct sides facing toward the back of the canvas. Also, there may occasionally be some slight inconsistency in the height of the lift. This is easily fixed by filing or sanding the frame corners before stretching canvas.

Expandable Joints

A stretcher that is well designed shouldallow for additional expansion, in the eventa canvas becomes loose and goes slack, orshrinks and tightens from changes inhumidity.

The most common style of stretcher joint isa mortise and tenon with mitered face. Thisstyle of joint is designed to be assembledwithout glue, friction-tight but flexibleenough to accommodate later adjustmentwith keys or other mechanism used forspreading corners.

Keys

Stretcher strips and pre-stretched canvasesoften come with small wedges (2 percorner) that can be inserted to gentlyexpand the frame dimensions to increasetension on a canvas that has become loose.Important: before keying out paintings withtightly fitted picture frames, make sure theframe rabbet is large enough to allowexpansion. The canvas may not fit if it'skeyed out too far.

Cross Braces

Paintings of large dimensions may needcross bracing to prevent bowing anddistortion from the tension of canvas andfrom the weight of hanging. Depending onsize and proportions, a single horizontalbrace may be sufficient, or intersectingbraces may be needed. Heavy dutystretchers should be braced to supportdimensions over 30". Some stretchers areavailable with mortise and tenon or lapjoints cut to fit braces, but simple bracingcan even be attached with very basichardware like T-plates.

Alternative designs:

In addition to all-wood stretchers with cutjoints, metal stretchers are also availablewhich use hardware joinery and keys.Aluminum/wood combination stretchers aremore costly than wood, but they offersuperior strength and resistance tohumidity.

Couldn't find an answer? Ask the Experts here