Stretcher or strainer?

Mar 19, 2012 2 Comments by

The auxiliary support of a canvas painting is usually a wooden frame onto which the canvas is stretched. This holds the canvas under tension, thus reducing movement of the fabric and allowing the artist to paint on a flat support.

There are two common types of auxiliary support. Strainers are rigid frames with fixed corners. Stretchers are frames that have expandable corners, allowing adjustment of tension. Usually keys (small wooden triangles) are present in slots in the corner joins. In order to expand the stretcher, these are gently hammered further into the join, thus pushing the stretcher members further apart and expanding the dimensions of the auxiliary support. This keying out places the canvas support under greater tension.


Keys in stretcher join

In Southeast Asia, it is very uncommon to find canvases on expandable stretchers. Strainers are much less complicated to manufacture, while stretchers require more advanced woodworking skills. Some art suppliers sell imported stretchers or poor quality locally produced ones, but it is rare for artists to make use of these.

However, stretchers do provide benefits over strainers. Cyclical changes in environmental conditions as well as degradation of the canvas support may result in sagging and loss of tension over time. Some very large canvases may be difficult to stretch onto an auxiliary support with adequate tension. Many contemporary artists create large-scale canvas paintings nowadays, and the use of stretchers would be beneficial in these cases.

Stretcher bar marks

If a canvas is under insufficient tension, or the strainer members are not cut at an angle (beveled), the canvas is likely to come into contact with the wood. Over time, this will result in the formation of stretcher bar marks, which are cracks in the paint following the contours of the stretcher members.

Auxiliary supports that are original to the painting are a valuable source of art historical information. They may reveal some of the artist’s working methods, or have labels, inscriptions and stamps attached which may act as supporting evidence of provenance, while also providing historical evidence of material availability. As such, they are an integral component of the painting as a whole, and should not thoughtlessly be neglected or replaced.

Strainer attacked by drywood termites

It is possible to adapt strainers in several ways to make them more suitable for the painting. However, there are occasionally instances where it may be necessary to replace an original auxiliary support with a new stretcher. In this case, the original should be carefully documented and photographed, making sure that all the necessary information revealed by the auxiliary support is recorded.

Canvas eaten by termites

We have come across numerous historical auxiliary supports which have suffered extensive insect damage, are warped, broken or are causing damage to the support through nails or weak joins. It is also possible for a strainer to have been completely hollowed out by drywood termites. In one such case, the termites had begun eating into the canvas where it was in contact with the wood, resulting in extensive losses to the original support and paint layers. In such an extreme case, there is no question of retaining the original auxiliary support.

Whenever the need arises to have an auxiliary support replaced, I opt for a stretcher instead of a strainer, as it allows adjustment of the tension. After a long search for a good carpenter in Kuala Lumpur, we were finally lucky to meet Yuqi Chock, a talented woodworker, furniture designer and restorer based in Petaling Jaya. After discussing my requirements and specifications for stretchers with her, she is now supplying us with beautifully crafted stretchers in custom sizes. More information on her work is available on Spero Woodwork.

Replacement stretcher




Conservation, General

About the author

Bettina is a professional paintings conservator, who is also qualified in art history. She set up the paintings conservation unit for Asiarta Foundation. Her specialist field of knowledge and research is Southeast Asian paintings, particularly art works from Vietnam.

2 Responses to “Stretcher or strainer?”

  1. Hilda Hayson says:

    Thank you for info. Is there a reference that helps to date artwork by the type of frame it is stretched on? ie a Fredrix stretcher w/ keys would date from what date? stapling canvas to stretchers began what date? I feel sure someone has catalogued the chronological appearance of different stretcher types, ie Phelger 1886.. but I don’t see a resource. I am trying to date an oil signed J. Egan on a Fredrix stretcher. thank you. HHayson TN.

    • Bettina Ebert says:

      Dear Hilda,
      Thanks for your interest in my post on stretchers.
      In the UK, an extensive resource has been compiled of artists’ suppliers from 1650-1950:
      However, Fredrix is an American company, so I could not find any reference to this in that list.
      There is a publication from the US on stretchers and strainers, though I could find no useful reference in that on Fredrix. The publication is this: Painting Conservation Catalog, The Paintings Specialty Group of the American Institute of Conservation, Volume 2: Stretchers and Strainers, compiled by Barbara Buckley, 2008, ISBN: 978-0-9760501-1-7
      The bibliography lists a couple of publications which may be quite useful for your purposes:
      Katlan, A. W. 1987. American artists’ materials suppliers directory: 19th century. Park Ridge, NJ: Noyes Press.
      Katlan, A. W. 1992. American artists’ materials, Vol II. A guide to stretchers, panels, millboards, and stencil marks. Madison, CT: Sound View Press.
      Apparently the 1992 publication patents from the 18th and 19th centuries on variations of stretcher designs.
      On page 16 of the publication by Buckley, it says: “In America, keys first appear in the late 18th century when keyable wooden stretchers of several kinds were being used concurrently with strainers…..In the 19th century, American inventiveness produced a plethora of designs to improve the traditional single- and double-keyed wooden stretcher.”
      Another source of information might be Fredrix themselves:
      Apparently they started producing keyed stretchers by 1875. It might be worth getting in touch with the company.
      One thing to remember though, when trying to date your painting, is that the stretcher may not be original to the painting. You might see evidence of old tack or staple holes on the tacking margins, which would help clarify this issue.
      Hope this helps!

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