Use of lipase to remove oil-based overpaints
| Main Authors: | , |
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| Format: | Book Chapter |
| Language: | English Slovak |
| ISBN: | ISBN 1-84407-253-3 |
| Online Access: | http://www.viks.sk/chk/14tmh_31.doc |
| Abstract: | SUMMARIES. In this case study, excellent results were obtained for the removal of oil-based overpaints using lipase L 0763 Type XII® (Sigma) applied as an aqueous gel. The penetration of gel components was reduced by using a relatively thick gel (5 per cent Klucel G® (Hercules)) and by avoiding the use of tensides in the gel mixture. Surface wetting was achieved by a pretreatment of the overpaint. Gel buffering to pH 7.7 was balanced without use of acids. A warm buffered gel softens the oil overpaint, however, in this case insufficiently to enable quality cleaning and much less efficiently than the same gel after the addition of enzymes. The maintenance of the optimal activity temperature of the applied enzyme gel proved to be neither convenient nor desirable (at 39 °C the gel becomes dried, humidity penetrates, temperature oscillates, and so on). Far better results were obtained with an optimal activity pH and without heating. CONCLUSIONS. The use of enzymes for cleaning painted surfaces should not be regarded as an alternative to organic solvents, but rather as a relevant and powerful supplement. In the case of the lateral altar from the Čiovo church, the appropriate lipase proved capable of removing the oil paint layer from the oil resin paint layer. The previous removal of surface deposits with triammonium citrate enabled the wetting of the overpaint surface. The reduction of gel penetration was achieved by applying a thicker, 5 per cent solution of Klucel G® (Hercules) and without using the tensides to improve the surface wetting. The use of acids to balance the pH of a gel can be avoided since the unbuffered gel can be added to reduce the pH of the mixture. The pH value of the gel becomes stable after a day or two, probably due to a more complete dissolution and distribution of TRIS throughout the gel. For the lateral altar from the Čiovo church, the buffered gel (without lipase) slightly softened the oil paint layer, however, this was insufficient to enable a satisfactory mechanical removal. Therefore, it can be concluded that in this case the enzymes did enable the removal of the overpaint and that they were aided by both a mild alkali hydrolysis and the water itself. This case indicates that the enzyme can function as an efficient catalyst even if only one of its optimal activity conditions is met. Of course, it is much more practical to achieve optimal pH than to achieve and maintain the uniform and stable warm temperature over the whole altar. Moreover, better results were obtained by avoiding the heating process and the consequential problems arising from heating and accelerated gel evaporation. |
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| ISBN: | ISBN 1-84407-253-3 |
