"Why would you choose a canvas with wedges ? Surely if it is stretched properly, they're unnecessary?"
This is true, to a degree. Ultimately, whether to choose wedges or not depends on a number of factors, including the dimensions of your canvas; its profile (depth),; your medium and painting style; whether the finished work is due to be transported at any stage; handling, geographical location with respect to environmental & temperature changes (sunlight, cold and humidity can all affect the fibers of your canvas) and, as it becomes heavier during the painting process, the cloth may move and loosen, regardless of how perfectly it was originally stretched.
But that's not all that properly made, installed and functioning wedges are good for ... another fantastic benefit is that a wedged stretched can be dis- and re-assembled. This is especially handy for art that is exported in a tube - and largely facilitates the re-stretching process once your work reaches its destination (especially given that decent stretching facilities are often either lacking, sub-par or extremely expensive abroad)
Wedges, "spacers", "chocs" or "keys" are adjustable “wedges” of wood that are fitted into the corners of canvas stretchers. These are used for “re-tightening” your canvas should it have become loose or ‘bouncy’ over time, during transit, as a result of environmental fluctuations or simply because of pressure applied to it during the painting process.
Most pre-made, cheaper canvases have “slots” cut into them (where wooden or even plastic wedges are supposed to go) and the wedges themselves supplied separately, often loose within the canvas packaging... leaving you with the often impossible job of fitting them into their ‘designated spaces’ before being able to tap them in.
We do things differently at ETH. We used a unique dovetail system which provides for the wedges to be pre-fitted at all the necessary points (8 wedges installed in each corner, and 2 wedges installed per cross bar). No glue is used in the wedge-system, and only a single "stabilizer" staple which is designed to pop out when the wedges is tapped in. This alleviates some of the stress of ensuring that the tightened canvas has equal tension all round and that they don’t splinter or crack the corners of the frame when you are tapping them in (a common complaint I hear time and again). In addition, we use only kiln-dried obeche timber (so most of the moisture has been removed) which is knot- free eliminating the natural tendency of cheaper "knotted" timber stretchers to split - usually at the moment you try and whack in a wedge.
Each set of our wedges are individually cut during the manufacture of each stretcher and I can promise you - they work like a wedge is supposed to! ETH Canvas is one of few (if not only) local supplier that are able to manufacture box (deeper edge) frames with a wedge system – right up to a profile of 50mm. In addition, and unlike other systems, there is little to no chance of damaging the canvas when you hammer the chocs in, since they are designed as a complimentary functioning set and sanded to ensure they don't damage your cloth. Another anomaly of pre-made, mass-produced chocs supplied with cheaper canvases.
A nicely tightened canvas vibrates like a drum membrane if you flick the center of it with your fingers. The less vibration, the more tightening that is required.
How to use a wedge-system to re-tighten a stretched canvas
If your canvas is unprimed, do NOT use the wedges until priming is complete - the priming process itself causes contraction of the cloth, rendering the canvas tauter on the stretcher.
For smaller canvases and using a rubber hammer, gently tap the end of both wedges into each corner, working your way around to each corner. As you tap the wedge, the space at the corner of the stretcher may increase. Don't be alarmed. This means its working.
It is advisable to check the progress of your tightening after each wedge position and that you stop once the canvas is taut enough – once the wedge is embedded, it cannot be removed and if you "over-tighten", it can create too much pressure within the stretcher structure and end up warping your frame.
NB - For larger canvasses, you need to expand the facing stretcher bars first, to keep the tension on the canvas even. So, tap the wedges that push one of the stretcher bars in one direction, then rotate the canvas and do the same for the wedges pushing the opposite bar, in the opposite direction. Then, repeat for the other sides.
It is never a good idea to tap too hard, for obvious reasons, since you always run the risk of overcorrection or the wood splitting – tap means “tap” (not bludgeon...). Please be wary of this, and rather tighten and rotate a second time, to be on the safe side.
How to extend the longevity of your painting.
Keywords are: COOL and DRY
AVOID
- Direct sunlight or sudden or extreme changes in temperature
- Leaning panels and stretchers against walls and directly on the floor (use blocks to raise them)
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