This paper presents an analytical investigation of paint reconstructions prepared with linseed oil that have undergone typical 19th century treatments in preparation for painting. The oil was mechanically extracted from the same seed lot, which was then processed by various methods: water washing, heat treatments, and the addition of driers, with and without heat. A modern process lead white (Dutch source, Schoonhoven) and a commercially available vine black were used as pigments. The reconstructions were prepared in 1999, and naturally aged from then onwards. We compared thermogravimetric analysis (TG), which yields macromolecular information, with gas chromatography-mass spectrometry (GC-MS) and direct exposure mass spectrometry (DEMS), which both provide molecular information. The study enabled us to quantitatively demonstrate, for the first time, that the parameters used to identify drying oils are deeply influenced by the history of the paint. In particular, here we show that the ratio between the relative amounts of palmitic and stearic acid (P/S), which is used as an index for differentiating between drying oils, is extremely dependent on the pigments present and the age of the paint. Moreover the study revealed that neither the P/S parameter nor the ratios between the relative amounts of the various dicarboxylic acids (azelaic over suberic and azelaic over sebacic) can be used to trace the sorts of pre-treatment undergone by the oil investigated in this study. The final results represent an important milestone for the scientific community working in the field, highlighting that further research is still necessary to solve the identification of drying oils in works of art.

Aims: To set up and employ, for the biorestoration of cultural heritage (altered frescoes), an advanced and innovative biotechnology method based on the sequential use of whole viable bacterial cells and specific enzymes. Methods and Results: The bioremediation intervention consisted of the direct application onto an artwork surface of whole bacterial cells of the Pseudomonas stutzeri A29 strain (bioaugmentation), followed by, in a final step, a purified Protease enzyme. The bioremediation was performed on a Spinello Aretino fresco that had become altered by the animal glue residues of past restoration. For the reader's interest the fresco is the 14th century Conversione di S. Efisio e battaglia (Conversion of S. Efisio and battle), size 3·5 × 7·8 m at the Pisa Camposanto Monumentale, Italy. An assessment was made of the final costs of the biological tests (whole bacterial cells, enzymes) so as to compare them with other intervention techniques. Conclusions: A successful innovative biological approach to recover valuable frescoes was set up, and the best conditions for treatment efficiency were identified. Furthermore the cost of the biological cleaning using viable bacterial cells and enzymes (P. stutzeri, Protease, Collagenase, 1 : 3 : 10, ratio respectively) was much lower than that of other conventional methods, making this biotechnology not only very interesting but also very competitive. Significance and Impact of the Study: New biotechnologies with an innovative, soft approach to the ‘biocleaning’ and ‘biorestoration’ of cultural heritage are in constant demand, and our results are clear evidence that such an approach has been achieved; the technique could be of significant importance towards developing other goals.