Organic artists’ materials include: supports, such as canvas or panel; adhesives; surface coatings; and paint media.
Organic supports are traditionally fibre, (usually flax, but can also include hemp, jute, and cotton) and a variety of wood types such as oak, poplar, chestnut, pine and lime.
The adhesives, coatings and media include naturally sourced protein glues, egg tempera, oils, resins and waxes. Since the Institute specialises in Old Master paintings, the synthetic analogues are not often encountered in the original works, although they may be present as materials which have been added by conservators during a restoration campaign. The Institute’s facilities to analyse organic materials are limited.
Gas Chromatography can be used to identify naturally-sourced and modified drying (unsaturated tri-glyceride) oils, including the most commonly used linseed, walnut and poppy oils. Gas Chromatography can also identify standard artists’ pre-treatments of these oils, such as partial pre-polymerisation caused by ‘heat-bodying’ oil. Gas Chromatography can also indicate the presence of naturally-sourced terpenoid resins such as those found in mastic and dammar, etc. However, in the absence of a coupled Mass-Spectrometer, these materials cannot be unambiguously identified.
Some adhesives, surface coatings and paint media may be generically identified using staining techniques applied to microscopic samples or paint cross-sections. Natural fibres can also be readily identified from their microscopic morphology and in cross-section. Students and interns are encouraged to use these methods routinely in conjunction with other methods of material identification.