Stručni rad
https://doi.org/10.17018/portal.2015.15
High Altar of the Assumption of Mary from the Parish Church of the Assumption of the Blessed Virgin in Vrbnik: Valorization of the Use of Poly(2–ethyl–2–oxazoline) as Substitute for Animal Glue
Nevena Krstulović
orcid.org/0000-0002-5632-7761
; Hrvatski restauratorski zavod, Restauratorski odjel Rijeka, Rijeka, Hrvatska
Sažetak
The ethics of conservation requires that all work methods and materials be reversible and compatible with the original materials. Therefore, conservators often opt for the use of nontraditional materials, in addition to combining these with traditional ones. This paper gives an account of the use and valorization of Poly(2–ethyl–2–oxasoline), i.e. PEOX, trade name Aquazol, as a substitute for traditional animal glue. Aquazol is a relatively new material in conservation practice. It was produced by the company Polymer Chemistry Innovations, as a very effective water–soluble polymer. It has been increasingly used in practice due to its good characteristics, as it is: soluble in polar organic solvents (acetone, ethyl alcohol, even water), thermostable, nontoxic, and fully reversible, while remaining elastic at low RH. Laboratory testings indicated that it becomes hygroscopic at increased RH (above 75–80%). It is also stable in the presence of weak acids and bases, in addition to being known as a compatibilizer polymer (a substance that aids in the better compounding of two different phases). Owing to its favorable physical and chemical properties, its long–term reversibility and solubility in acetone, it is safe for application over sensitive surfaces, such as polyment gilding. On the high altar of the Assumption of Mary from the parish church of the Assumption of the Blessed Virgin Mary in Vrbnik, i.e. on its central portion, Aquazol was used as glue, while undergluing the painted layer. More precisely, the central portion of the altar that consists of the attic, cornice, two half–columns with composite capitals, and the predella, was originally completely gilded (investigations revealed two layers of gilding), but was later, during the construction of lateral wings, painted with white–and–red and blue–and–white marbleizations in places, and red and green washes that were applied directly onto the gilding. The whole painted surface was covered in a thick coat of altered varnish and deposits of atmospheric dirt. The painted layer was found to be very unstable, i.e. it was largely crackled in trough–like bulging and, in places, completely disintegrated pieces. Therefore, in the first phase of work, it was necessary to stabilize and underglue the painted layer. A decision was made not to use traditional glue (rabbit–skin glue) for the preventive undergluing of the painted layer, as this would later make the removal of altered varnish more difficult. The solution of Aquazol in distilled water, with prior moisturizing of the surface treated with ethyl alcohol, proved to be the optimal solution in this case. More precisely, the extra glue from the painted surface and the gilding was removed with acetone, which causes no damage to the gilding. After that, there was no problem to start removing the altered varnish and the surface dirt. In order to further test the use of Aquazol as a substitute for animal glue, trials were performed of making the putty for the wooden support of the chalk base and the polyment gilding. To make the putty for filling the injuries of the wooden support, binders were used based on a solution of Aquazol 200 and acrylic resin Paraloid B–72 and binders based on Aquazol 200 and Plexigum PQ 611; as fillers, Champagne chalk, Bologna chalk, and phenolic microballoons were used in different ratios. Putties based on Aquazol 200 and Plexigum PQ 611 proved to have better cohesive and adhesive properties. Trials of polyment gilding and base were done on three small wooden panels. Two panels were isolated with a solution of shellac (orange), and one with a solution of rabbit–skin glue. As binders for preparations and polyments, Aquazol 200 solutions were used, in distilled water, ethyl alcohol, and a combination of these, in different ratios. As fillers for the chalk preparation, Champagne and Bologna chalks were used, as well as phenolic microballoons, in different ratios. To make the polyment, Armenian yellow and red bole was used. With the trials completed it can be argued that Aquazol as a synthetic material is a good substitute for animal glue, and that when polished with agate it can obtain high gloss, same as with the traditional polyment gilding. Advantages are its long–term reversibility and solubility in acetone that would not cause damage to the surrounding original gilding when being removed. The only downside that needs to be considered is that when moisturizing the polyment with alcohol (when applying gold leafs), PEOX gets activated and lightly smeared across the edges of the previously applied leafs. This can be avoided by working carefully and using a solution of distilled water and alcohol, given that Aquazol is somewhat slower to solve in water. When choosing the protective coating, only resins soluble in nonpolar solvents should be considered.
Ključne riječi
conservation work; Vrbnik; high altar of the Assumption of Mary; animal glue; polyment gilding; PEOX; Aquazol
Hrčak ID:
149932
URI
Datum izdavanja:
21.12.2015.
Posjeta: 2.454 *