Thin sectioning was an early procedure used to analyse fossilised material contained in coal balls.[50] The process required cutting a coal ball with a diamond saw, then flattening and polishing the thin section with an abrasive.[51] It would be glued to a slide and placed under a petrographic microscope for examination.[52] Although the process could be done with a machine, the large amount of time needed and the poor quality of samples produced by thin sectioning gave way to a more convenient method.[53][54]