Print, Photographic

Black and white photographic print mounted on fabric depicting two men at a microscope in a research laboratory in the chemical laboratory at the Champion Spark Plug Co.
Caption reads: Photograph 30
The Petrographic Microscope is used to determine the structure of the porcelain. Sections are cut off of the core and polished down until they are only one-thousandth of an inch thick. They are thin enough so that when illuminated on one side they can be studied from the other side with powerful glasses which magnify several hundred times.
The chemist can determine the gravity of materials and the chemical composition, but he cannot tell about the structure. This must be done by the microscope.