Pyrex® flat, clear Petri dishes with cover from Corning® . Made of borosilicate glass, these dishes will withstand repeated sterilization (wet or dry). The edges are beaded to provide greater mechanical strength. The bead also provides a means to equally space the side walls of the bottom and cover, thereby reducing the capillary action of the condensed moisture on the sides. They are not affected chemically or thermally by any of the methods commonly employed in laboratories where sterilization is routinely used. The covered dish is not airtight. The covers are marked in blue enamel and the bottoms in white enamel to make sorting easier. Bottoms also have a triangular enamel reference point for serial dilutions. Untreated surface. Reusable.