Star cracks

Glassware and Equipment: "Standard taper glassware, especially round bottom flasks, are susceptible to 'star cracks'. These are tiny, radiating defaults in the glassware. Before setting up a reaction, carefully check your glassware for star cracks. If you find one, you can trade (no charge!) for a new piece of glassware. To prevent star cracks, always handle the glassware carefully."