Beckstoffer has figured out that a certain altitude--from about 600 to 730 meters--in the right part of Lake County has a heating-and-cooling cycle similar to Napa's.
And they reckon that, overall, the surface of the sea becomes two or three times warmer at the high point of the cycle than mere solar heating can account for.
The glaze is applied to a fired stoneware vessel, which is then fired again in a repeated cycle of six stages of heating and cooling where precise temperatures matter a great deal: either over- or under-firing will spoil the effect.