Agar, a natural polysaccharide, has gained increasing popularity among conservators worldwide in the past two decades as a gelling material for water and aqueous solutions. Converting the aqueous medium into thermo-reversible hydrogels enables cleaning and humidification treatments to be performed with very strict control of the amount of water released. Even sensitive surfaces of different types of artworks can thus be treated with a good degree of selectivity. When the surface possesses sufficient cohesion and is compatible with a temperature of approximately 40°C, the semi-solid state of the agar gel represents the ideal means of application. From a practical point of view, however, restricting the application to limited areas may be difficult; furthermore, a homogeneous application to large areas may be even more problematic: in this near-solid state, the gel remains workable for only a short time. This contribution addresses both situations by introducing specific tools and the related methodology to treat both very small and large areas. A heated syringe-pistol can be easily assembled for the former situation, and a commercially available paint sprayer can be used for the latter. This novel spray application has been considered in detailed studies. It produces a flexible, ductile film with quite a different morphology from that of the film traditionally produced by warm application and cooling. The syneresis process is thus affected by the different gel structure. The extremely controlled release rate of water from a spray-applied hydrogel makes this application highly compatible with even the most sensitive surfaces.

Calcium hydroxide nanoparticles dispersed in ethanol or 2-propanol have been proposed for deacidification treatments of cellulose-based supports and are currently adopted by many paper and paintings conservators. There is however a risk inherent in this treatment: the dispersion would acquire a highly alkaline pH in the presence of moisture, absorbed by the dispersing alcohol solvents or by the cellulose-based support. Consequently, conditions of potential risk would be created for the structural integrity of the cellulosic supports, for some organic film-forming materials and some colouring matter. The simple tests conducted in this study clearly demonstrate that this risk is real, and suggest a cautious attitude in evaluating the suitability of these nano-dispersions for the treatment of some works of art.

Comparative studies of tumor-initiating activity in mouse skin and carcinogenicity in rat mammary gland were conducted with 7,12-dimethylbenz[a]anthracene (DMBA) and selected derivatives. Female SENCAR mice were initiated with DMBA, 1,2,3,4-tetrahydro-DMBA, 2-, 4-, 5-, 9-, and 10-fluoro DMBA, (FDMBA), and promoted with tetradecanoyl phorbol acetate. The same compounds were tested by intramammillary injection in female Sprague-Dawley rats. DMBA, 9-FDMBA, 10-FDMBA and 1,2,3,4-tetrahydr DMBA were strongly tumorigenic in both mouse skin and rat mammary gland, whereas 2-, 4- and 5-FDMBA were weakly active or inactive. In a third experiment DMBA, benzo[a]pyrene, 1,2,3,4-tetrahydro DMBA and 9,10-dimethylanthracene were tested by repeated application on the dorsal skin of Swiss mice. DMBA was the most carcinogenic, followed by benzo[a]pyrene and 1,2,3,4-tetrahydro DMBA, whereas 9,10-dimethylanthracene was inactive. The potent activity of 1,2,3,4-tetrahydro DMBA suggests that the bay-region diol epoxide pathway may not play a significant role in the activation of DMBA in these two target tissues. Some of these compounds can serve as useful models for elucidating the mechanism(s) of activation of DMBA.

Many painted surfaces, not necessarily only those with a contemporary binding media, display high sensitivity to water. The resulting damage, including swelling, leaching out of some components, even partial solubility, may lead to a shrunken, impoverished, de-plasticized, more porous paint film. Different approaches to the cleaning of such surfaces have been developed throughout the years, as awareness of this sensitivity grew worldwide. Some deal with the proper physico-chemical conditions of the aqueous solutions, and others with the proper ways of delivering these solutions to the surface. The strategy proposed in this technical note is concerned with the latter, the application stage, and is based on the combined and simultaneous use of a device capable of delivering a constant, precise amount of the aqueous cleaning solution and a surgical micro-aspirator to immediately remove the soiled solution from the surface and speed up its drying. Also, using a different apparatus, non-polar solvents can be delivered, for cleaning surfaces contaminated by non-polar, more lipophilic soiling materials.

In the preservation of cultural heritage, the measurement of pH has implications both as a parameter for assessing the state of conservation and as a reference for the preparation and use of aqueous treatment solutions. Few studies in the relevant literature, however, deal with evaluating the reliability of measurements. The purpose of this study was to identify the best method and the confidence limits for measurements of surface pH on linen canvas. The results obtained with the two main methods currently used, water drop and rigid gel, were evaluated and compared with warm extraction. Agarose at different concentrations was used for preparing rigid gels, and the influence of the volume of the gel was also evaluated in the latter measurements. Five canvas samples with different degree of acidity were tested: highly acidic, acidic, weakly acidic, a new linen canvas, and the lining canvas recovered from a painting dating around the middle of nineteenth century. The theoretical surface pH values (pH_st), derived from the measurements obtained by the aqueous extraction method, were used as standards against which to assess the reliability of the measurements.