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Stretcher bar
A stretcher bar frame is a wooden framework on which an artist fastens a piece of canvas.
Stretcher bar, schematic. Shapes are drawn for illustration.
What the sources say
| Point | Detail | Source |
|---|---|---|
| Wood | Typically well-dried softwood, often Nordic pine, which resists warping | Wikipedia |
| French stretcher | Mitred corner joints are not glued, so the canvas can be retensioned | Wikipedia |
| Keys | Small wedges in the corner joints give the canvas its final tension; most corners have two keys, some older stretchers one | Wikipedia, CCI |
| Cross brace | Fit one on lengths over 40 in (1 m) | Wikipedia |
| Humidity | CCI advises 40 to 60 percent relative humidity; low humidity shrinks the wooden stretcher and can cause rippling and corner draws | CCI |
| Keying out late | CCI calls keying out after size, ground and paint are applied highly inadvisable for fixing slackness | CCI |
For wall art
The bars decide how far a stretched canvas stands from the wall and how it behaves in damp air; the humidity guide covers the placement side, and the canvas comparison covers bar depths.
Where the sources stop
Wikipedia gives the general definition. The CCI note is about conserving finished paintings, so its humidity range and keying-out advice are for paintings, not for decorative canvas prints. Tate's page on the term could not be fetched, so two sources are used.
Sources
- Wikipedia: Stretcher bar (fetched 2026-11-12)
- Canadian Conservation Institute Notes 10/9: keying out of paintings (fetched 2026-11-12)
Figures from these pages are paraphrased; each page was fetched and read on 2026-11-12. Where two sources differ, both are shown.