I know that high fire stone ware is oven safe and dishwasher safe, but is it microwave safe?
There is a specific accepted protocol for testing if something is labeled "Microwave Safe". If you don't follow this protocol here in the USA... I'd be careful of formally labeling ceramic wares as "Microwave Safe". Maybe more like "Can be used in a microwave".
http://www.astm.org/Standards/C1607.htm
best,
......................john