RESULTS AND DISCUSSION

Figure 1 and Figure 2 show casts taken from teeth that were cleaned by the traditional brushing on of ethanol method. These casts appear to be free of consolidant at low magnification (Figure 1.1 and Figure 2.1), but at higher magnifications (Figure 1.2, 1.3, Figure 2.2, 2.3) the microwear is clearly being obscured by smeared consolidant.

Figure 3 and Figure 4 compare the quality of microwear obtained from tooth surfaces that have been cleaned via the application of solvent gel to that from adjacent uncleaned areas. It can be seen from these images that the use of solvent gel leaves little or no remaining consolidant. The ability of solvent gels to lift consolidant cleanly rather than dissolve it and allow it to in-fill microwear can be seen in Figure 5. Here we show a selection of teeth that were marginal to areas cleaned with solvent gel, such that only part of the tooth surface has been cleaned. In each case there is no smearing or blurring, the edge of the consolidant coating is sharp and well defined. All of these casts showed large areas of tooth surface that were either completely free of consolidant or that had only small, discrete patches of consolidant within them.

A combination of acetone, ethanol and xylene makes a good universal solvent gel, and holding the pH down to a value around 8.5 slows the action of the solvent gel, causing the shellac to swell and blister. This amount has proven more effective at removing thick coatings of shellac than using more alkaline solvent gels. These tend to act more rapidly, penetrate the shellac and remove it unevenly.

A note of caution on the removal of shellac: Conservators are aware that removing any consolidant from a fossil may cause damage. In the case of aged shellac that damage can be significant. This is due to the tendency of shellac to shrink over time, exerting pressure on the fossil. In some cases, if this pressure is removed the fossil can fracture and disintegrate (Davidson and Alderson 2009). For microwear analysis there is no alternative to removing the consolidant, but by using solvent gels the area of removal can be restricted to very small parts of the tooth, minimizing the risk. None of the hundreds of teeth to which our solvent gel cleaning method has been applied showed any evidence of resulting damage.

Solvent gels concentrate the action of the solvent on the specific part of the surface being cleaned and in doing so reduce the diffusion of the solvent into the surrounding area. Where a tooth or jaw has been reconstructed by gluing several parts together, use of a solvent gel will enable cleaning of a portion of the tooth without compromising the reconstruction.

By retaining the solvent within the gel, the volume of evaporate is greatly reduced, conserving the solvent and allowing cleaning to be performed with simple air extraction rather than a fume cupboard (subject to all relevant health and safety legislation, especially where xylene is used within a solvent gel). A more comfortable working environment is the result.