Non-destructive speckle imaging of subsurface detail in paper-based cultural materials

We have used Laser Speckle Contrast Imaging (LSCI) to investigate the statistical properties of dynamic speckle reflected from an obscuring scattering surface in order to reveal drawings that are hidden beneath. Here we explore the limitations of this method used with various algorithms when applied to a selection of paper samples. These samples consist of a sketch executed in an assortment of media laid on a base surface that are then hidden beneath a subsequent top layer. The ability to resolve gray scale images was examined as well as the contrast surface temperature relationship. A book with glued pages was investigated in order to demonstrate the technique's applicability to the non-destructive examination of cultural materials. While being shown as a useful tool in revealing obscured drawings the scattering properties of the surface layer present a limitation in its general applicability.