Tightening key

A tightening key is a small wedge or shim used in the construction of a canvas stretcher frame with expandable joints. The key is inserted into the slotted inside the stretcher bars at the mitered corners of the frame to prevent or adjust sagging.^[1][2][3] Tightening keys are commonly made in plastic or wood, and are often called corner keys or corner wedges.^[3] Tightening keys were introduced in the mid-18th century, making expandable (versus rigid) stretcher frames possible.^[4]

The back of a stretched canvas, with keys inserted at the corner, and additional keys off to the side.

Use

Most stretcher frames have eight keys, two in each corner.^[1] Each key is tapped in to expand the stretcher bars slightly, tensioning the canvas.^[1][2] The keys can be used to re-tighten the canvas as it relaxes naturally over time.^[5] If the key is tapped too forcefully, it may tear the side of the canvas.^[4] Conversely, keys that become too loose can fall out during handling and damage the painting's surface.^[1] The process of inserting keys into the stretcher is called "keying-out."^[4]

Types

Corner keys or wedges come in various forms. Most are manufactured for a specific size stretcher bar, making framers and artists hold various sizes in stock. A product called "wedgee" eliminates the need to stock many types as it has a male / female profile, which allows it to be pressed together to fit most corner cut-outs.^{[citation needed]}

See also

• Stretcher bar