APPENDIX

Carbopol was originally manufactured by B.F. Goodrich (now Noveon). It was available in several formulations (e.g., 934, 940, 950 and 954), and it is these that are discussed by painting conservators (Southall 1988; Wolbers et al. 1990). EZ2 is a newer but comparable formulation of Carbopol and is more readily available today than the older versions. It is supplied as a white powder. When mixed with pure water it forms a clear, slightly acidic, viscous gel. The water must be pure, otherwise any minerals present (particularly calcium) will react with the Carbopol and precipitate out. The manufactures claim that the EZ formulations disperse more quickly, which certainly appears to be the case (EZ2 can be used within minutes of mixing whereas 954 took over an hour to achieve a uniform consistency). Carbopol 954 based solvent gels were used within the Palaeontology Conservation Unit at the Natural History Museum, London, and Carbopol EZ2 based solvent gels were used on specimens at all other sites.

Ethomeen is manufactured by Akzo. There are two forms suitable for use in solvent gels (C/12 and C/25), with C/25 being recommended for use with the more polar solvents (Wolbers et al. 1990). Ethomeen is an ochre coloured viscous liquid and is slightly alkaline. Both forms are available from Linden Chemicals.