44th Annual Meeting – Book & Paper Session, May 17, "Targeted Cleaning of Works on Paper: Rigid Polysaccharide Gels and Conductivity-Adjusted Aqueous Solutions," Amy Hughes and Michelle Sullivan

The past few years have seen an uptick in the number of BPG session talks focusing on cross-disciplinary materials and techniques that allow for more targeted treatment approaches. Specifically, the use of rigid polysaccharide gels, such as agarose and gellan gum, and conductivity-adjusted waters are techniques with a more established history in paintings and objects conservation that are being adapted for treatment of works on paper.
Michelle Sullivan, Graduate Fellow in the Department of Paper conservation at the J. Paul Getty Museum, spoke first about the use of gel systems in targeted cleaning of works on paper. Sullivan outlined the advantages of gel systems, which include:

  • targeted, precise application by cutting gels to shape
  • restricted lateral movement, minimizing tideline formation
  • increased dwell time for reagents in solution and solvents
  • no mechanical action, protecting paper fibers
  • colorless, transparent/translucent gels facilitate treatment monitoring
  • ease of removal, virtually no residues

While the science behind these gel systems is best left to the experts in the postprints, here are a few notes worth keeping in mind when designing treatments with gels:

  • Agarose is more opaque than gellan gum; gellan gum’s translucency allows you to more closely monitor treatment.
  • Casting thinner gels affords greater control over solvent diffusion.
  • Pore size is inversely related to concentration; the higher the concentration, the smaller the pore size, which leads to greater capillary action.
  • You can use a range of modified aqueous solutions with the gel systems, including pH- and conductivity-adjusted waters, chelators, and enzymes.
  • The gels can be used with polar solvents; just soak the prepared gel in solvent of choice overnight. Sullivan noted that the gels become more rigid when soaked in solvent, so she recommends cutting them to the desired shape and size prior to soaking.
  • Examination under UV revealed more consistent washing with the gel than with a traditional blotter wash.

Sullivan then presented two case studies. First, by tracing the outline of a stain onto a sheet of polyester film and then using this template to shape the gellan gum, she was able to reduce the stain locally without the risk of tidelines. In the second example, Sullivan humidified a print and then washed it overall by placing it face-up on a sheet of gellan gum. A medium-weight sekishu paper was placed between the print and the gel. (She tried Hollytex as a washing support, but it did not allow for consistent penetration.)
Experimentation is currently underway to determine whether or not gel residue is left behind on the paper substrate. Agarose, gellan gum, and methylcellulose are being tagged with UV-fluorescent dyes in order to track their movement onto the paper; results of this testing should be available  in 2017.
Next, Amy Hughes, Andrew W. Mellon Fellow at The Metropolitan Museum of Art, spoke about her research into the use of pH- and conductivity-adjusted waters in treatment. Adjusted waters minimize swelling of the paper fibers while at the same time improving wetability and solubilization of degradation products, allowing conservators to design treatments that are more sensitive to the object. Again, I’ll leave the scientific explanation to the expert (though I have to note her lovely illustration of osmosis featuring a very plump carrot), but the procedure involves measuring surface pH- and conductivity of the object using agarose plugs and handheld meters (this video from the Getty clearly outlines the process) and then combining ammonium hydroxide (weak base) and acetic acid (weak acid) to form ammonium acetate (neutral salt) that, with water, can be used to create an isotonic solution (a procedure also outlined in a Getty video). Hughes did note that some objects washed in adjusted waters retained a vinegar odor that took 3-5 days to dissipate; further testing is underway to address this issue.
These talks left me feeling very inspired to begin testing out these new treatment methods in my lab!