Coyote Glazes crystals in glaze

I was just informed by a customer in Las Cruces NM that every time she went to use her glazes she had to screen them. Remaining in the screen was a cup full of what looked like clear crystals. I had never seen this so had no idea...  She called over to Frank at Coyote Glazes and he explained that when it is very cold the gerstly borate creates crystals and they need to be put in the microwave and melted then put back in the glaze. Who ever heard of such a thing?