Keys or Wedges

Paintings are often painted on fabrics stretched on a stretcher. With time the fluctuation of humidity and temperature makes the canvas relax. The relaxed fabrics on the stretcher create deformation on the paint layer. Those deformations can create irreversible damage. The more common are cracks on the edge of the stretcher. The wedges or keys are used to open the stretcher bar to create a good tension to the canvas. However, it is important to not overstretch the artwork. If this is the case, it could tear after a redraw of humidity or higher temperature. The best humidity relative is 55% for the conservation of the painting but to adjust the tension of the painting.

There are different shapes and materials wedges like wood or plastic, the more common use is made of wood. The long side of the wedge is touching the stretcher before being inserted in the slut in the corners. When in place they need to be hammered in. This step must be realized with care to not damage the reverse of the canvas. Two wedges are required in every corner. If the stretcher has a cross bar more wedges will be required for every side of each bar.

With time the keys may dislodge themself and fall between the canvas and the stretcher. This miss placement can create the deformation of the canvas, tears, cracks and possible paint loss. To prevent this from occurring drill holes at the end of each key. In those holes passed a thread and attached it to the side of the stretcher. This thread can help in the future to remove the wedges if necessary.