A tightening key is a small

wedge A wedge is a triangular shaped tool, and is a portable inclined plane, and one of the six simple machines. It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place. It functions by converti ...

shim Shim may refer to: * Shim (spacer), a thin and often tapered or wedged piece of material ** CPU shim, a spacer for a computer heat sink ** Shim (fencing), a device used in the sport fencing ** Shim (lock pick), a tool used to bypass padlocks * Sh ...

used in the construction of a

canvas Canvas is an extremely durable plain-woven fabric used for making sails, tents, marquees, backpacks, shelters, as a support for oil painting and for other items for which sturdiness is required, as well as in such fashion objects as handbags ...

stretcher A stretcher, gurney, litter, or pram is an apparatus used for moving patients who require medical care. A basic type (cot or litter) must be carried by two or more people. A wheeled stretcher (known as a gurney, trolley, bed or cart) is often ...

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. Tightening keys are commonly made in

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...

, and are often called corner keys or corner wedges. Tightening keys were introduced in the mid-

18th century The 18th century lasted from January 1, 1701 ( MDCCI) to December 31, 1800 ( MDCCC). During the 18th century, elements of Enlightenment thinking culminated in the American, French, and Haitian Revolutions. During the century, slave trad ...

, making expandable (versus rigid) stretcher frames possible.

Use

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

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.

References

Picture framing Painting materials {{art-material-stub

Use

Types

See also

References