I think in my case it was just I got the plastic to Hot also it could be that there was something wrong with the curing of the glass sometimes there are flaws in the Pyrex . I might want to mention the careful of using some of the glitter make sure that it is safe to use with hot plastic some of the glitter that you guys are using make up metal I have caused a few fires in my microwave with different glitter silver we usually throw that in the garbage if the glitter is not good do not buy aftermarket glitter from craft stores.