The recent Gels in Conservation conference, held at the Emmanuel Centre in London from the 16th – 18th October, was a rich source of information for the conservator. Speakers included both conservation scientists and conservators, so the conference addressed a good deal of scientific research, as well as methods, recipes, and tips for using gels in practice. Representation of conservators from all disciplines provided a great opportunity for the cross-fertilising of ideas and techniques. More than 500 delegates were in attendance, and we all fit comfortably into the beautiful historic venue, with its oak-panelled walls, domed ceiling and bible inscriptions running across the walls. Given the large number of presentations, this review will only touch on my personal highlights from the conference. However, preprints available from Archetype Publications contain all 41 papers and 34 posters.
The conference was held over three days, with each day focusing on a different gel group: poylsaccharide gels (e.g. agar, gellan, xanthan); polysaccharide and polyacrylic gels (e.g. Carbopol, Pemulen); novel and multi-gel treatments. The kenote speaker was, not suprisingly, Richard Wolbers, a pioneer of many of the gel systems and techniques employed by conservators today. His talk encouraged the conservation community to adopt the following principals of “green chemistry”: reduce the amount of solvents used in treatment; use catalysts instead of reagents; use non-toxic or less toxic chemicals; use bio-sourced, renewable chemicals rather than petrochemicals; and use biodegradable materials. In his own practice, Wolbers is increasingly moving away from toxic solvents in preference of water-based systems, including during aged natural resin varnish removal. Wolbers has a vision for the future to create a water-based varnish for paintings to stop the solvent cycle.
Italian conservator Paolo Cremonesi delivered the second talk of the conference, and offered interesting insights into agar gel and the differences between agar and agarose. Conservators who have used agarose, a purified form of agar, will be familiar with its high cost. However, as agarose is also non-ionic, or electronically neutral, it remains the best choice for making gel plugs for pH testing. Chris Stavroudis, another gels pioneer working in private practice in the United States, demonstrates this technique in a useful YouTube clip. According to Cremonesi, agar is best prepared in the microwave and once the powder is dissolved, it can be utilised for cleaning in several ways. Prepared agar can be cast into a petri dish, then cut and used: as either a flat rigid gel placed over the artefact; as a cleaning block like a smoke sponge; or grated from the block and swept over a surface. Alternatively, the prepared agar solution can be brushed warm onto an artefact and left to set. This last technique is especially useful if the object being treated is not perfectly flat or has impasto. Cremonesi cautions about using this method for works on paper and heat-sensitive artefacts. To solve the latter issue, agar gels with lower gelling temperatures may be appropriate. Cremonesi also highlighted that agar is thermoreversible, meaning it can be heated and cooled numerous times. It does not keep well, so a good rule of thumb is to “make it and use it”.
Paper conservator, Amy Hughes, reported on her study into the accuracy of the agarose pH test mentioned above when used for paper. She pH tested 16 different papers using both the traditional cold extraction method and the new agarose method. Hughes found that the agarose plug method has difficulty measuring alkaline paper, concluding that it is only reliable in the 4.5-6.5 pH range. However, I believe it is still a useful tool in practice, as one usually does not have a disposable paper sample for the cold extraction method, and the electrode method can be both fiddly and more likely to leave tidelines.
A number of talks also addressed the question of gel residues. For example, Michelle Sullivan from the Getty presented her research into residues from gellan gum, agarose and methylcellulose when applied to paper. Experiments were carried out on three different paper types and the gels were tagged with fluorescein to help detect residues after treatment using ultraviolet light. Sullivan was able to conclude that while all three gels do leave residues behind, these can be minimised by using a barrier tissue and clearing with a damp cotton swab. The ageing tests indicated that paper treated with agarose ages well, while handmade paper treated with gellan darkened on ageing. In question time a delegate asked whether the tissue inhibited the treatment, but Sullivan reported that for her it did not, provided she used the right thickness of tissue. Interestingly, on the previous day during question time, both Wolbers and Cremonesi said they would not recommend using a tissue barrier. As neither Wolbers nor Cremonesi are paper conservators, they are perhaps not dealing with such a porous material. Cremonesi did mention that he had tested for agarose residues when used on plaster and found only trace amounts left behind after treatment.
Yana van Dyke, paper conservator from the Metropolitan Museum of Art in New York, gave an excellent talk on the use of agarose-enzyme gels for reducing adhesive on water-sensitive artworks, like Indian miniature paintings. The electronically neutral agarose gel is an ideal choice for holding the enzyme because it does not interfere with the enzyme’s catalytic ability. In particular, van Dyke recommends the low gelling temperature agaroses because the enzyme is easily incorporated after initial gel preparation, without the worry of denaturing at higher temperatures (agarose powder requires an initial high temperature in order to dissolve in water). In question time, van Dyke provided some very useful practical tips, including: buying a highly purified enzyme to minimise residue left behind on your object; measuring and weighing your enzyme in the vessel you are going to cast the gel in to avoid losing fragments through static charge; increasing the concentration of the gel the closer you get to the surface of the water-sensitive work, making the gel drier and therefore less risky.
Perhaps the most visually impressive talk of the conference was that given by Lu Allington-Jones from the Natural History Museum (NHM), London, featuring the cleaning of a slice of the giant sequoia tree. The sequoia is the largest tree on earth and in 1893 a specimen, 1,341 years old from California, was cut down into segments for exhibitions at the American Museum of Natural History and the NHM (as Allington-Jones noted, their collecting ethics have changed somewhat since then!). The NHM section has been on display ever since and had accumulated a lot of dust. It also had a deteriorated varnish that was obscuring the growth rings. The removal of the varnish was carried out using a gel composed of Carbopol, Ethomeen, industrial methylated spirits, and low concentrations of distilled water. The advantages of the gel system were numerous. As Allington-Jones pointed out: it enabled increased contact time between solvent and varnish; it reduced toxicity (because the solvent was bound in the gel – this was particularly useful as the treatment was undertaken in the public space); it reduced mechanical action compared to swabbing with free solvents; and was suitable for working on a vertical surface. A wonderful time lapse video of the three month treatment was shown, to much appreciation from the audience.
On the evening of the second day there was a special lecture by Tate staff on the Nanorestart project, an initiative involving 26 partners from 12 different countries aimed at finding solutions for treating contemporary works of art using nanotechnologies. Tate Painting Conservator, Rachel Barker, presented an interesting case study featuring the cleaning of a Roy Lichenstein acrylic painting with newly developed gels based on polyvinyl alcohol. These gels are known as the Peggy Series, after their use at the Peggy Guggenheim Museum. They are made by the Centre for Colloids and Surface Science (CSGI) in Italy, but are not yet commercially available, nor are they easy to prepare by conservators in standard laboratories. Barker found that the Peggy 6 gel performed the best for cleaning and left no detectable residues even when triammonium citrate was added. While the Tate lectures are unfortunately not in the preprints, the research will be published elsewhere.
On the last day, conservation scientist Lora Angelova from the National Archives in the UK, spoke about xPVOH-borax gel, another type of polyvinyl alcohol gel which combines the characteristics of soft gels such as methylcellulose with those of rigid gels like agar or gellan. As Angelova explained, the xPVOH-borax gel is not strictly speaking a gel, but rather a highly viscous polymeric solution, similar to children’s play material ‘Slime’. This gel-like material is ideal for cleaning textured or three-dimensional surfaces while limiting residue, though it may not be suitable for more porous materials. The impetus for developing this gel was to have a pliable gel that you didn’t have to scrape up. The xPVOH-borax gel can be prepared by the conservator, and can be tailored to a specific treatment by adding solvents or chelating agents. Recipes are included in the preprints. In practice it has found application for cleaning oil paintings on canvas and frames (great for getting into nooks and crannies!) and like the agar gel, it has been used as a wet eraser for works on paper.
Paolo Cremonesi also gave a brief impromptu talk on the last day about the toxicity of the silicon solvents, cyclomethicone D4 and D5 (not in the preprints). These solvents are used as a preliminary step to applying a gel to prevent tidelines. According to Cremonesi, the conservator should wear gloves and respirator when using these solvents and not put them down the drain as they bioaccumulate. They should instead be allowed to evaporate in the air (according to a previous speaker, D4 is retained in the support for 40 minutes). D4 is no longer available in Europe due to potential harmful affects on an unborn child, while D5, to the best of current knowledge, is considered non-toxic to humans.
Overall, the conference outlined the following advantages of gels over cleaning with cotton swabs: they avoid the snagging of cotton fibres on impasto peaks, they are less disruptive to acrylic paintings, and they avoid the scratching that can occur when cleaning metals. They can also offer very even, controlled cleaning, and gel systems are highly tunable, for example: the use of thinner films or higher concentrations to reduce liquid interactions; the addition of chelating agents, enzymes, buffers; and in the case of xanthan gum, the formation of an emulsion by incorporating both water miscible and immiscible solvents. Of course, as one audience member noted, gels are not applicable to every situation. However, as noted by Chris Stavroudis, it is important for conservators to at least experiment with gel techniques. Although understanding gels may take time initially, their application may save considerable time in the end. As put eloquently by Richard Wolbers at the close of the conference: “a tool is a function at one end and a handle at the other and the tool has to be comfortable in our hands, it needs to get us in and out of jobs”. Ultimately, I felt the conference was well worth attending, not least because of the lively question sessions, the extra talks not published in the preprints, and the chance to meet international conservators.
We look forward to welcoming Wolbers to Melbourne in January 2018 when he will be delivering a series of workshops to further disseminate his knowledge.
Briony gratefully acknowledges the support she received to attend this conference from the Gordon Darling Foundation and her employer, the Grimwade Centre for Cultural Materials Conservation.