The extra pieces of wood supplied with an art canvas are called canvas keys or wedges. They are small triangular or rectangular wooden pieces that are used to adjust the tension of the canvas once it has been stretched over the stretcher bars. Here’s how they are used:
- Adjusting Canvas Tension: Over time, changes in temperature and humidity can cause the canvas to expand or contract, potentially leading to a loosening or sagging of the fabric. The canvas keys are inserted into slots in the corners of the stretcher bars, and when turned, they push against the bars, exerting pressure on the canvas. This helps to tighten or loosen the canvas as needed, maintaining an even tension across the surface.
- Preventing Sagging: By using the canvas keys to adjust the tension, you can prevent the canvas from sagging or becoming loose. This is important for keeping the canvas flat and providing a stable surface for your artwork.
- Re-Tensioning the Canvas: If the canvas becomes noticeably loose or saggy, even after the initial stretching, you can insert the canvas keys and turn them to re-tension the canvas. This process allows you to restore the tautness of the canvas and ensure an optimal painting surface.
It’s important to note that not all canvases come with canvas keys, especially pre-stretched and pre-mounted canvases. However, if your canvas does come with canvas keys, they provide you with the option to adjust the tension of the canvas over time, maintaining its optimal condition for painting.