11 DISCUSSION

Withdrawal of the use of Synperonic N has made us consider the properties demanded of a generalpurpose conservation surfactant. The present selection has been based mainly on cleaning ability of the pure surfactant in distilled water solution acting on standard soiled textiles. Better cleaning could, no doubt, be obtained by adding performance-enhancing additives such as a suspending or chelating agent, but the ranking of the surfactants could then be altered.

It is important to note that the experiments do not reveal whether any residual surfactant remains behind after rinsing. In most but not all cases, significantly more soiling is removed where a surfactant is used in the washing liquid, i.e., more than water alone. Aging of the washed model textiles did not show enhanced deterioration compared with water alone. Residues may remain after rinsing because of porosity—e.g., stone, ceramics, or metals—or, in the case of anionic surfactants, because of deposition of an insoluble metal soap. Although not experimentally evaluated in this study, it should be noted that if multivalent metal ions are present in significant quantities, the nonionic surfactants might be the better choice.

Users may find that some of the five surfactants appear to have little to distinguish them in the tests; some of them have peculiarities that may make users prefer one to the others. Orvus WA has a high level of foam, Synperonic 91/6 has foam that disappears rapidly on rinsing and a slight odor, Imbentin C135/070 can be difficult to dissolve, and Dehypon LS45 often produces a cloudy solution in water. Dehypon's cloud point (at 1% concentration or at 5 x CMC = 0.3%) is 20–22�C; thus, in warm weather, Dehypon produces a cloudy solution and in cold weather a clear solution. The cleaning action of nonionic surfactants is greatest around the cloud point (Jakobi and L�hr 1987) but decreases rapidly above the cloud point, until at 5�C above it there is effectively no surfactant action. Thus, Dehypon LS45 should not be used at too high a temperature. A summary of the data can be seen in table 7.