Kovács Petronella (szerk.): Isis - Erdélyi magyar restaurátor füzetek 20. (Székelyudvarhely, 2020)
Focht Anna: Gorka Géza padlóváza restaurálása
Around 1846 Christian Friedrich Schönbein, a German-Swiss chemist, discovered the cellulose nitrate when he spilled a mixture of nitric acid (HN03) and sulphuric acid (H2S04) into a cotton apron. Nitrocellulose was the starting-point for the semi-synthetic substances produced in the second half of the 19th century with varied components and using different production methods. In 1862, Alexander Parkes produced Parkesin (created from nitrocellulose and camphor, with added dyes and other agents), generally considered as ’synthetic ivory’. In 1870, an American, John Wesley Hyatt patented a semi-synthetic material called Celluloid manufactured with the inclusion of cellulose nitrate and camphor using high temperature under pressure. Celluloid is also suitable to imitate ivory, marble, mother-of-pearl and tortoise shell. Ivoride, another celluloid compound is also used as a substitute for ivory. Today, there are endless lines of artificially produced fully synthetic materials. One of the earliest is the fully synthetic caoutchouc. The white version of Bakelite produced between 1920 and 1930 was a popular replacement for ivory-like materials. For the same purpose a German product, Kallopast (a mixture of methacrylate bead polymer and monomer methacrylate containing a catalyst) was applied in Hungary in the 1970’s. The texture of substitutes listed above is optically different from that of ivory objects. Nowadays manufacturers are consciously intending to create materials deceptively similar to ivory in terms of both machinability, colour and texture, to protect wildlife. Elforyn as such is a mixture of minerals and resins containing UV dyestuff for distinction. There are ongoing experiments with bio-inspired synthetic materials consisting of hydroxyapatite powder (Ca5(P04)30H) and gelatine to supplement piano keys. Mária Emilia Szabóné Szilágyi Wood and furniture conservator MA Wooden sculpture conservator MA Translated by: Eszter Tóth Katalin Orosz - Zsuzsanna Várhegyi The use of gels in paper and leather conservation Cleaning with solvents, removing contamination, adhesives or coatings by aqueous or organic solvents are hazardous, but often used treatments by conservators. In recent decades, considering the guidelines of the so-called ’green chemistry’, it has become increasingly desirable to use environmentally and health-wise less hazardous solvents, and to reduce the amount of chemicals. This has diverted attention to the use of gels in the restoration process. The study presents the written sources, the author’s experience using agar, and gellan rigid hydrogels, which is commercially available and can be prepared easily. The paper describes their structure, operating mechanism, method of production and possibilities of their application in paper and leather conservation. The properties of degraded paper and leather effected by moisture and the dangers of wet treatments are rewied. Some of the model experiments conducted by the authors are presented and the results are shared. A 4-5% w/v solution of gellan and agar gels placed in a microwave or on a hot plate can be prepared for use by heating it to approx. 90 °C and pouring it into a flat glass bowl. The 3-5 mm thick gel sheet can be used on a flat surface to dissolve contamination or to introduce treatment agents (e.g. complexing agents, enzymes) into the material of the artefact. Hydrogels with a concentration of 2% w/v are suitable for enzymatic treatment. During any such treatment, it is advisable to cover the gel with a Plexiglas or glass cloche to prevent the solvent from evaporating. Because paper and leather are porous materials, they are able to bind a lot of moisture, therefore their wet treatment carries more risk. The use of hydrogels on paper is determined by the absorbency and water sensitivity of the paper. A paper object may be sensitive to moisture due to the writing materials on it (water-soluble inks; swellable, soluble binders of paints; loosely bound pigments such as pastel, charcoal, graphite) or the weakened condition of the substrate (acidic, moldy, ink-corroded paper). Although gels are often recommended in the literature for the treatment of water-sensitive papers, this is often too risky for the above-mentioned cases. The gel does not seem to be suitable for treating paper containing water-soluble inks or paints. It can also be risky during local treatment because it is difficult to prevent lateral water transport and thus the formation of another water stain, especially in poorly sized papers with good absorbency. For pastel, charcoal, and graphite drawings, it can only be applied from the back (verso) by placing the graphics on the gel sheet. It is then advisable to pre-humidity the paper to stretch it so that it is in even contact with the gel. In this case the artefact lays on the gel sheet, therefore it can be damaged when removed, if the wet strength of the paper is not high enough (e.g., acidic, moldy sheets). In such cases, we can use Japanese paper for the handling, which is located between the graphics and the gel during the whole cleaning process, but a longer treatment time must be expected. For leather, the use of hydrogels poses several risks and is not recommended for use on alum tawed, untanned, red rotted, loose, damaged, cracked, and gilded, painted leather. For the treatment of a well-preserved tanned leather with closed grain surface or parchment bookbindings a 4-5% w/v solution of gellan gel may be suitable for a few minute-long treatment, however, due to its strong wetting ability, even then, the agar gel is not recommended. On metal-combined leather artefacts, the thermoreversible agar gel mixed with a complexing agent is suitable for removing corrosion products from copper parts. In this case, the material can still be applied to the metal in a lukewarm, densely fluid state (before gelation), where it solidifies quickly and can then be easily removed after treatment. 235
