AIC's 53rd Annual Meeting

Paper conservators working with different concentrations of agarose gels have observed that stain removal efficacy increases as the gelator concentration is increased. Although the exact process(es) contributing to this increase in efficacy have not been studied previously, many physical phenomena are thought to play a role, including diffusion and capillarity processes involved in the transport of solvent and solubilized components to and from a substrate placed into contact with a gel. We propose that the process of adsorption plays an important role in the sequestration of water-soluble products once they have migrated into the gel. The adsorption of solubilized components by the gel network essentially purifies the bulk solvent in the gel, increasing the uptake of more material and preventing redeposition. 

Adsorption measurements of solid agarose indicate that it could remove 90% of crystal violet (hexamethyl pararosaniline chloride, C25N3H30Cl) from an aqueous solution rapidly. Even when engaged in a gel network, agarose is capable of functioning as an adsorbent. Critically, a gelator can do more than act as a vehicle to deliver solvent: it can also trap solubilized components via adsorption onto its polymer chains. By adding a range of additional adsorbents, including microcrystalline cellulose powder and silica gel (200400 mesh), at 1 wt% into agarose gels, we have shown we can increase the adsorption rate and total cleaning capacity of these systems. One consequence is we can reduce the amount of gelator required for a treatment.

If the mechanisms at work within gels are better understood, it may be possible to design systems that amplify the effects of stain removal treatments while reducing the need for expensive and/or unsustainable materials. Agarose, a component of the algal extract agar, is costly due to the purification process involved in isolating the polymer and the limited availability of the algae from which it is derived.[1] However, agarose is often preferred for gel treatment of paper due to its minimal deposition of residue and the good aging properties of those potential residues.[2] This research offers an approach to decrease the quantities of this important resource needed to carry out a conservation treatment. The applicability of adsorbent-bulked agarose gels in hands-on conservation practice is being tested, and the effectiveness of specific adsorbents for certain applications is being investigated. Through the close collaboration between scientist and conservator, conservation practice informs scientific experimentation, and analytical results can impact treatment methodologies.

[1] Santos, R., Melo, R.A. Global shortage of technical agars: back to basics (resource management). J Appl Phycol 30, 2463–2473 (2018). https://doi.org/10.1007/s10811-018-1425-2

[2] Warda, J., Brückle, I., Bezúr, A., & Kushel, D. (2007). Analysis of Agarose, Carbopol, and Laponite Gel Poultices in Paper Conservation. Journal of the American Institute for Conservation, 46(3), 263–279. https://doi.org/10.1179/019713607806112260