New Investigations of Adhesives for Tear Repair of Canvas Paintings

The thread-by-thread tear mending technique for canvas paintings represents an important field of research for the preservation of canvas paintings. This joining technology has been published and has become well established as a minimal invasive alternative for the treatment of local damage in the canvas, in contrast to the application of patches or the lining of paintings. Since then the technique has been further investigated, especially with regard to adhesive evaluation. For the first time, this paper presents the examination of five different test set-ups for the adhesive evaluation in an overall context: 1. uniaxial tensile tests on free adhesive films, 2. on mended yarns, 3. on fabric strips, 4. biaxial tensile tests, and 5. multiaxial burst pressure tests. The bonding was carried out on flax threads and canvas samples. For this purpose, single thread bonds were prepared within the specimens with a selection of different synthetic polymer dispersions and sturgeon glue modifications. Different bonding techniques were investigated, such as overlapping or butt joint mending, with and without bridging threads. The aim of the investigation was to understand the individual influencing factors in the various test series. Furthermore, the focus was on the development of a suitable test system for the evaluation of adhesives for the thread-by-thread tear mending treatment in textile painting supports. It can be stated that only the testing of several bonded threads in a fabric composite should be pursued as a long-term sensible test arrangement. This is in contrast to the previously very common set-up of testing mended single threads. Promising adhesives and adhesive modifications have been found for butt joints and overlap joints. The additional strengthening effect of bridging threads on butt joints has been proven and quantified.