A stretcher bar is used to construct a wooden stretcher frame used by artists to mount their canvases. They are traditionally a wooden framework support on which an artist fastens a piece of canvas. They are also used for small-scale embroidery to provide steady tension, affixing the edges of the fabric with push-pins or a staple gun before beginning to sew, and then removing it from the stretcher when the work is complete.
Since a stretcher is simply a frame, it can be constructed in a variety of ways. The differences in construction have to do with how the corners are built.
The mitre joint is the most popular method of adhering corners on a stretcher, although butt joints are also fine if used in conjunction with gussets. Keys or small triangle wedges are inserted in the joint after stretching the canvas to give the canvas its final tension. When fastening the canvas, pressure should be distributed evenly around the stretcher to minimize warping due to unequal distribution of pull.
Unlike other types of frames, the corner joints in stretcher bars are not glued or fastened in any permanent way. This allows the canvas to be retensioned over time, as it has a natural tendency to stretch and sag over time. In contrast, strainer bars stretch canvas in a fixed (non-adjustable) way.
The use of stretcher bars in the home print market has become increasingly prominent with inkjet-printed canvas prints becoming more popular in the home.
Although artists use blank canvases and pre-stretched canvases in the art business, many photographers use stretcher bars for framing wedding photography and reproduction of photographic prints. Stretcher bars are also used in picture framing when framers are framing things like sport shirts etc. Stretcher bars are used extensively in theatrical productions for framing material backdrops.
When a photographer takes a picture then digitally transfers this onto a canvas (inkjet printing), he then stretches this over a stretcher frame. By wrapping the canvas all the way around the frame, known as gallery wrap, the photographer can then hang his picture on the wall – already framed.
The profiles on the stretcher bar should be slightly rounded. This has two advantages: 1) It allows the framer to see and obtain clear edges on images that have precise borders, and 2) It also allows the canvas weave to “roll over” the profile rather than snap over a sharp edge which is a major cause of canvas cracking.
