Reactivity of earth and synthetic pigments with linseed oil

The influence of lead ions on the drying of oils

“…A similar study, but using heating at 125°C to accelerate the reaction, showed lead salts forming from pigmented oils with red lead, litharge, lead white and Naples yellow but, interestingly enough, not with white lead sulfate, which may explain the poor performance of the pure sulfate as a drier [98].…”

On the stability of mediaeval inorganic pigments: a literature review of the effect of climate, material selection, biological activity, analysis and conservation treatments

“…Ochres are stable to light, moisture, alkali, and dilute acids, and are inert in mixtures. Their stability to acids is testified upon oxalic acid exposure, which causes only the formation of Ca-oxalates, from the other components of the ochre [32,67]. They are, however, sensitive to high temperatures, such as fires [12,68], or local heating effects related to the use of lasers for cleaning [19,69,70] or for spectroscopical analysis (i.e.…”

“…It promotes oil curing and it retards its oxidation [20]. Verdigris (neutral and basic), as well as the copper carbonate pigments azurite and malachite, shows the tendency to react with the oil binding media to form copper soaps [35,67,145], to brown and darken, as Cu + is formed by ambient light absorption (photoreduction), and oxygen promotes the formation of brown peroxide species [146]. Cu-salts of organic acidic compounds are formed in verdigris-containing paint layers (or at the interface with the varnish), as fatty and resin acids can extract copper ions from the verdigris pigment [133,147].…”

“…On wall paintings, the combined presence of humidity and salts can cause the formation of degradation products, sometimes coloured as in the case of NaPb 2 (CO 3 ) 2 OH and PbO polymorphs, with cerussite being the most stable of them all [123,218]. Leadwhite tempera and oil layers show the formation of lead soaps, which negatively affect the appearance of the paintings [55,67,226]. Leadwhite tempera applied on fresco paintings yields PbO 2 , as the reaction takes place in alkaline environment [213].…”

“…Plattnerite might be formed if acidic pollutants attack the paint layer [242]; or when biological colonization is present [238]. Red lead is readily affected by organic acids (including the oil binder), which causes the final appearance of lead carbonate, via lead acetate Pb(C 2 H 3 O 2 ) 2 [109] and lead hydroxide Pb(OH) 2 [55], and/or lead soaps [67]. Two types of yellow pigments based on lead and tin are available, type I which is an oxide (Pb 2 SnO 4 ), and type II which is a stannate silicate of lead (PbSn 1−x Si x O 3 ).…”