The Consolidation of Flaking Gouache on Japanese Paper
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0034-5806 |
| Online Access: | http://www.viks.sk/chk/res_4_02_240_255.doc |
| Abstract: | CONCLUSION. Our tests highlighted the characteristics of each strengthening agent (Table 4) and can help to select the most suitable one. Polyvinyl alcohol at 1% clearly enhanced the adhesion and reduced the probability that the gouache would cleave or flake. Its effect on the two-colour gouache, however, was quite disappointing. The methyl hydroxy ethylcellulose at low viscosity (3cP) enhanced the gouache adhesion for die single- and two-layered samples; it did not improve their cohesion, and sometimes even weakened it. Gelatine was a good strengthening agent for flakedgouache and also improved the adhesion, which has already been observed by others". We observed, however, that it did not diffuse very well, and therefore it seemed not to be a good adhesive for the powdery gouache. This kind of gouache needed a strengthening agent which was good at diffusing in order to improve its cohesion. To choose the right adhesive for our special case, we also had to consider how each strengthening agent would resist ageing. The chemical stability of polyvinyl alcohol12 in the presence of pigments and that of Paraloid B72' when applied on paper is not proved; so these two were rejected. Finally, we decided to use gelatine to consolidate the gouache paintings made by Claude Autant-Lara. This strengthening agent gave the second best results in terms of cohesion and adhesion (ranked just after the polyvinyl alcohol), and at the same time it absorbs and desorbs atmospheric water in an amount comparable to that of the paint layer, so that there will be noor only little internal tensions. A non aqueous strengthening agent such as Paraloid B72 could induce microscopic tensions in the flakes, blocking the movements of the paint during its exchanges with atmosphere. Thus, we concluded that gelatine, over a long period, would be the safest and most appropriate strengthening agent. Finally, we would like to emphasize, what is probably the most important conclusion of this study, that adding a strengthening agent is an irreversible operation,which in some cases can actually weaken the paint layer. An improperly chosen strengthening product can induce tensions in the gouache layer, and reduce its internal cohesion and/or its adhesion to the paper. It must also been taken into consideration that for the tests a long fibred paper was used, which improves the adhesion. Therefore, our conclusions on how each strengthening agent can improve the adhesion may be too optimistic for gouache on paper of a lesser quality. In many cases, especially if no flakes are noticeable, it seems safer to keep cracked gouache painting in the best climatic conditions and under optimum mechanical protection rather than consolidate it. If it appears that the gouache layer has flaked to such a degree that it should be consolidated, comprehensive tests should be performed, because the choice of best strengthening agent depends strongly on the physical properties of the gouache, and the paper in any given case. SUMMARIES. The consolidation of flaking gouache on Japanese paper Some gouache works, made in the 1930s by Claude Autant-Lara, were damaged in die paint layer. Extensive areas of gouache including areas of overlapping layers of paint were very cracked. Some of these were even flaking. In order to select the appropriate treatment, we compared the properties of five different strengthening agents, prepared to the same concentration (l°/o) or same viscosity (3 cp), resp. Samples of gouache, as close as possible to the work of art were prepared, submitted to accelerated ageing and then consolidated with the strengthening agents: gelatine, sturgeon glue, polyvinyl alcohol, methyl hydroxy ethylcellulose and Paraloid B72. Adhesive and cohesive strength were measured using a peeling test and a shearing test in a traction machine. The different kinds of break and their areas were studied in order to evaluate the particularities of each product and the best one for the case in question. |
|---|---|
| ISSN: | ISSN 0034-5806 |
