41st Annual Meeting – Research & Technical Studies, June 1, “Contemporary Conservation for Contemporary Materials” by Yvonne Shashoua

Attending a lecture by Yvonne Shashoua, Senior Researcher in the Department of Conservation at the National Museum of Denmark, was such a treat, since she is so well-known in the field of plastics conservation, and her session did not disappoint.  Her calm, precise, and very approachable speaking style was impressive as she covered a scientific discussion on her current research into cellulose acetate degradation and its interaction with gas absorbents.  Since she will be presenting her findings in upcoming journals, I will only briefly go over what I learned and what you missed at this Research & Technical Studies AIC session.
Shashoua began by reminding us that plastics comprise an increasing proportion of museum collections.  Since it is difficult to detect plastic degradation until it reaches an advanced stage, a preventative approach, by either removing the factors causing or accelerating degradation, is usually taken.   Gas absorbents (silica gel, activated charcoal, Zeolite 4A, and Corrosion Intercept) are frequently used in museum storage and display situations to create a microclimate by removing specific gases.  She discussed how these materials are used and how they absorb pollutants, which I found very interesting.
Focusing on cellulose acetate, Shashoua discussed the mechanism of degradation (and the breakdown by-product acetic acid) and how additives (plasticizers and fire retardants, which are weakly bonded within the matrix) migrate out ultimately ending in shrinkage.  She was curious why the degradation process even begins in a museum environment, which began her in-depth research project. Cellulose acetate, has been used since 1910, but by the 1960s could be found in many objects: imitation mother of pearl, cigarette filters, early Lego bricks,  movie film bases and rayon.  By conducting a systematic study on the adsorbents’  interaction with cellulose acetate, she has found some startling results.  The adsorbents in some cases did slow down the onset of autocatalysis, however some also adsorbed the plasticizer and/or flame inhibitor, resulting in damage.  Her results suggest that commonly used absorbents in museums are non-specific and ineffective for cellulose acetate and, by extrapolation, other plastics.  She did rate the adsorbents  on a sliding scale; so reading her more in-depth post-prints will be a good lesson and/or review for all of us.  All this is startling news!  An archival acid-free box might simply be the best defense.  Wow.  I cannot wait to read her in-depth post-prints and journal articles concerning this fascinating subject.

41st Annual Meeting – Textile Session, May 30, “New and Current Materials and Approaches for Localized Cleaning in Textile Conservation” by Elizabeth Shaeffer (co-authored by Joy Gardiner)

I had the pleasure of attending Elizabeth Shaeffer’s session exploring current and developing approaches used in the localized cleaning of textiles.  Her fast-paced, well-delivered lecture provided a wealth of information on localized cleaning techniques from the traditional use of cellulosic materials (cotton sheets, blotter papers and cellulose pulps) to gel systems (both viscous and rigid).  She then concluded the session with a more in-depth discussion on a sampler treatment followed by comparison charts on the different methods.  I will not go into all the detail that she went into, but I will provide a brief overview.  We all should look forward to reading her post-prints as they will provide a more in-depth discussion.  Being an objects major with a subspecialty in textiles, I was excited to hear her talk, as the reduction of stains or adhesives is found in all conservation specialties including paper, objects and paintings.
Cellulose Poultices
Beginning with the use of cellulose poultices to reduce stains from a textile by capillary action during drying.  Shaeffer described a treatment performed by Joy Gardiner at Winterthur, with whom she conducted a lot of her research, where a series of cellulose poultices assisted in the reduction of a tideline on the upholstery fabric of a rather fragile chair.  The textile was dampened followed by blotter wicking for the initial removal of discoloration.  Blotter wicking was continued until no more discoloration was removed.  At this point, dampened cellulose pulp was used for better contact.  The difference between the before and after images were dramatic; the treatment was quite successful.
Viscous Gels
Unlike cellulose poultices, gels are used to deliver cleaning solutions (which might include chelators and enzymes) with the added benefit of being able to limit the amount of solution to water-sensitive surfaces and to increase the solution contact time.  Viscous gels still maintain a fluid-like property and can flow into the interstices of a fabric, which could make it difficult to remove.  She discussed the thick application of a methyl cellulose (MC) poultice on a dye sensitive sampler.  MC (50% concentration) can be made very thick and molded by hand into the desired shape.  The residue question can be reduced by the addition of a barrier, but this also can reduce the efficacy.  Enzymes can also be included in MC poultices and alpha-amylase is currently available in a pre-made system, the Albertina Kompresse.  Additionally, lowering the concentration of MC with shorter application times and the application of sodium chloride to the rinse solution can reduce resides.
Xanthan gum, another viscous gel, was discussed and it’s unique shear force properties, which was interesting.  When the gel is agitated on the surface of a textile, soils will be suspended in the solution phase and then trapped in the gel structure when the force is removed.  Also, xanthan gum is compatible with non-water miscible solvents such as benzyl alcohol or tolulene.  The gel structure has “pockets” in the network allowing oil in water emulsion. Reducing bleaches cannot be used as it will break gel.  Be sure a buy “highly purified” xanthan gum.  Consider adding a biocide, as it can grow mold.
Laponite RD was also covered briefly.  The benefit is that it is compatible with bleaches since it is inorganic.  Studies do show that residues left may cause discoloration, so the use of a barrier like gampi paper should be considered.
Rigid Gels
The first rigid gel discussed in the session was agarose, which is a product already familiar in conservation.  When dissolved in heated water and cooled, agarose forms a rigid three-dimensional polymer network with pores.  These pores can hold solutions and can be combined with chelators, enzymes and even water miscible solvents.  Depending on the concentration of agarose used, the pore size will differ thus affecting amount of solution released, and therefore can be tailored for each treatment.   Shaeffer described her experience with a chelating test kit developed by Richard Wobers with varying pHs.  She found that on a test linen, the higher pH was more effective no matter what the chelator.  When Shaeffer was an intern at the Philadelphia Museum of Art, she used this information along with the system that Laura Mina and Kate Sahmel developed for removing dye bleed, to remove discoloration of the ground fabric of a sampler.  (Laura Mina and Kate Sahmel presented their treatment at AIC last year.)  Shaeffer’s treatment was successful but very labor intensive since each small area was outlined with cyclododecane followed by the “cut to shape” agarose (with EDTA) gel..  Agarose is easy to manipulate and reusable, something to consider.  Finally, gellan gum was quickly mentioned as a recently introduced rigid gel finding its way into the consideration of conservators.
In Conclusion
The comparison charts, when the post prints are released, will be good to review again, since so many types of techniques, solutions and recipes were only briefly discussed.  In the post-prints, she will be discussing at greater length her research and treatments (including “recipes”).  Elizabeth’s warm delivery tone allowed me to be swept away into an in-depth discussion of gels and poultices used in textile treatments.  In this blog, I have seriously only briefly touched on the discussion.  It was a topic that embraces not just the textile specialty group, but other conservation specialties.  She hopes that some of the material discussed will spark our interest; encouraging us to share our findings as we proceed.  I, for one, will be now be considering these materials into my “toolbox” of techniques!