Patches versus single threads
On the side wings we had to restore a lot of open seams and holes in the canvas. Due to the large format of the theatre sceneries, their age, use and variable storage and climate conditions, holes have appeared and seams have weakened and opened over time.
In the last centuries, these damages were often treated with glueing or sewing of textile patches onto the original canvas. Today they tell us stories about the historical restoration of the objects. They are a sign of different trends in our profession. However, the patches can also cause trouble such as deformations in the canvas and are a challenge for the conservator.
Patches were often bigger than the hole, also covering the surrounding canvas area. The patch with the glue and the original canvas with paint forms as it were a sandwich. The diffusion rates are different for the sandwich than for the rest of the canvas. Further, they cause differences in tension and resulting in deformations in the original canvas. The unaesthetic visual effect on the surface of the painting cannot always be reversed. We can see these damages for instance on the backdrop (see image). Another negative point is the large amount of glue that was used to attach the patch on the back of the painting. It soaked through the canvas structure and made it stiff.
On the other hand, patches also have some positive aspects compared to other treatments. Applying the patches is a very fast method to stabilize unsecured tears, holes, etc. The attachment of a second textile to the painting´s back also a good support for the canvas.
After many years of experimenting conservators have found alternative treatments other than patches. One of them we applied to the damages of the side wings. Single threads were glued over the tears and holes and acting as a kind of stabilising bridge. This way of repairing holes has many positive aspects. We can use less glue, so we don’t saturate the canvas. With the thread bridges we add less new material to the original canvas, avoiding the sandwich effect and thereby deformations in the canvas. Another positive effect of using less material is that we do not cover original canvas and still can see and study the information on the back.
To fix thread bridges we used Beva 371, a special glue with good properties that are needed for the support of the canvas. The material is reversible; it doesn’t soak into the canvas but has enough adhesion. Beva 371 is in use since the 1970’s and has been thoroughly tested, the thread mending method has been introduced in the 1980’s, but what its aging properties are in the long term is not known. So far, the method of attaching thread bridges with Beva 371 seems to be a better way to repair holes in the canvas than patches.
Finally, we have to emphasise that just using the thread bridges is a good method to secure the tears and holes to avoid further damage, but it is not strong enough to withstand active use of the object. As these sceneries are going to be in a static display, this is not a concern here.