Application of confocal Raman spectroscopy to thin polymer layers on highly scattering substrates: a case study of synthetic adhesives on historic textiles

This study considers confocal Raman spectroscopy as a means of identifying a range of synthetic polymeric adhesives used in textile conservation. Many of the synthetic adhesives applied to support fragile textiles in the 1970s are now showing signs of ageing and the textiles are therefore being presented for retreatment. With no record of the adhesive used, conservators are unsure of the appropriate protocol to remove the original adhesive prior to retreatment. We have shown that Raman spectroscopy lends itself to the analysis of these thin polymer layers as it is inherently non-destructive and can be applied in situ. We also found that, for particularly thin polymer layers (∼20 μm), the underlying textile often scatters far more efficiently than the overlying polymer and therefore the polymer cannot always be identified unambiguously in situ. Although thick, transparent polymer samples are known to produce maximum Raman peak intensity when the laser is focused a few microns below the sample surface, focusing on or just above (0–5 μm) the polymer layer is shown to maximize the ratio of polymer peak intensity to textile substrate peak intensity, thus facilitating identification of the polymer. Defocusing further to a point 20 μm above the upper surface is shown to reintroduce interference from the substrate spectrum to a level comparable to that acquired when focused within the thin polymer layer, closer to the textile substrate. Copyright  2004 John Wiley & Sons, Ltd.