Some of the few remaining relics from the era of grinding and polishing the 200-inch mirror are these glass pyramids:
They were made of Pyrex glass by Corning Glass Works, just like the 200-inch mirror was. In the Optical Shop at Caltech they were fashioned into tools that were used for both grinding and polishing the 200-inch.
The two pictures below, Taken January 3 1938, show opticians creating the full-sized polishing tool. In the first picture the optician at right is placing one of these glass pyramids into a big metal disc to form a pitch lap.
The second view shows the broader view with three men working on the polishing tool. Several of the glass pyramids can be seen on the nearside of the tool.