The 7½ cent stamp shows a biaxial interference picture produced by a flake of muscovite mica in a petrological microscope, using a conoscopic lens and crossed nicols. The coloured bands are formed by interference in white light (Newton’s rings). The black bands, or isogyres, which move as the mineral is rotated on the microscope stage, represent positions in the mineral where the directions of light vibration in the mineral and in the nicols coincide, when no light passes. These brightly coloured interference pictures are used to identify minerals under the microscope.
Details
- Designer: From photographic studies by University of Rhodesia and Department of Geological Survey
- Printer: Mardon Printers (Pvt.) Ltd., Salisbury, Rhodesia
- Process: Lithography
- Paper: Chromo with brown gum
- Watermark: None
- Perf: 14.5 (comb)
- Cylinders:
- 1A (Black) 1A (Magenta) 1A (Yellow) 1A (Cyan)
- 1B (Black) 1B (Magenta) 1B (Yellow) 1B (Cyan)
- Sheet: R5 x10 (50)
- Quantity: 400,000
Sheet Numbers
