Glue Sheet Analysis
Peel photos can be examined in the field or later in the lab using Photoshop, GIMP or Paint.Net. X & Y locations of any red particle will be reversed left to right in our glue sheets; e.g. a particle at top right in a photo will be top left in a glue sheet. Software locations in pixels will correspond to glue paper locations plotted from the centre of the paper with ruler and protractor.
Where the glued soil is too thick to see through microscopically, semi-attached outer grains are removed by agitation, being careful to collect them for examination. Inner particles are seen by first removing outer soil grain by wetting. Particles are highly electrostatic and must not be pried from the glue sheet or they will be lost. They must be loosened with a drop of water and cotton swab, gently removing the particle from the swab with a pointer inside a small re-sealable plastic zipper storage bag.
The use of photos and glue sheets greatly increases chances of finding particles; e.g. a photo revealing one particle will often show several in its glue sheet. It should be possible to identify other colored particles like yellow ochre, charcoal, yellow and green pigments, etc using SEM and X-Ray diffraction, as long as the soil does not naturally carry these minerals. Sequential photos and glue sheets often show repeated painting or a natural erosional sequence. If the particles and wall art pigment are analytically identical, a carbon sample from the peel screening can be submitted for AMS dating. The method should apply to petroglyphs where pocked and unpocked faces highly contrast.