Examples of a historic fixed wooden strainer (a) and a new expandable stretcher (b)
A traditional canvas painting is attached and tensioned onto a wooden strainer or stretcher, generally made from softwood. Earlier supports had a fixed construction, with four or more wooden members, depending on the size of the painting, joined using various joints and sometimes adhesives or hand-forged nails. Over time, these fixed supports were largely superseded by expandable stretchers in which
the joined members can be adjusted to restore tension to the canvas when necessary, for example by means of keys or corner expansion mechanisms. Correct canvas tension is essential to avoid deterioration such as slackness and undulations that may lead to further damage over time. Adjustable stretchers also make it possible to restore tension without completely removing the canvas from its support each time.
Because loss of canvas tension is a progressive process, deciding whether to retain or replace the original strainer or stretcher is an important part of many conservation projects. In principle, preservation is preferable: even a simple original support can provide valuable information about the artwork.
Where complete replacement is unnecessary, an older fixed strainer may be adapted into an expandable support using metal tensioners or corner expansion devices.
When replacement is unavoidable, Dorica Restauri works with specialist suppliers of custom-made stretchers in finger-jointed, knot-free fir, designed for adjustment using suitable sliding pins.
