The use of laser pyrolysis–GC–MS for the analysis of paint cross sections

• Laser pyrolysis allows the localisation of organic substances in paint cross sections.
• Natural resins may be distinguished and localised.
• Synthetic colourants may be distinguished and localised.

The ability to analyse layers within a paint sample is important both for historical studies as well as determining the most suitable method for restoration. The difficulty in physically separating these very thin layers makes detailed analysis difficult, and a combination of destructive and non-destructive techniques are needed. Laser pyrolysis/gas chromatography - mass spectrometry (LaPy/GC–MS) is a technique that has proved successful in the analysis of geological samples which pose the same difficulties for analysis, but it has not yet been tried on paint cross sections. This study presents preliminary results of applying LaPy/GC–MS on standard mock-ups for identification of organic compounds used as varnishes, binders and colourants.The technique was shown to be particularly effective for the identification and localisation of natural resins and synthetic colourants. Moreover, the integration between this technique and other stratigraphical analyses may allow the complete characterisation of the composition of organic substances in paint cross-sections.