Clear dishes of this level can resist repeated sterilisation (wet or dry). The edges are beaded to make mechanical strength more prominent. The bead also makes it possible to position the base and lid sidewalls equally thereby reducing the capillary action of heavy moisture on the slides. These are not chemically or thermally effected by any of the methods that are commonly used in research laboratories where sterilisation is a significant part of routine or specialised work. The covered dish isn't airtight.
The tops are arranged in blue polish and the bottoms are arranged in white polish to facilitate arrangement. Bottoms also have a triangular, polished point of reference for serial dilutions.