Construction details of a petrographic microscope modified for high‐temperature investigations are described. Operational features and specimen preparation procedures are discussed. The equipment has an optical system that provides a magnification of X70 with means for recording the results photographically. The maximum operating temperature is 2000°F. Typical photomicrographs of crystals developed in soda‐lime container glass at elevated temperatures are shown along with a crystal growth rate curve of crystalline phases in this g