u/Ok_Slip2143

Got these two vintage casserole dishes, barely used, from a client but there isn't much description on the box other than naming them as having come from Regal Greetings and Gifts in Toronto, Canada. Which from a quick google search has been closed for decades. They don't have a series name I can find, there's no maker mark or anything identifiable on the backs to say whether it's safe to use in the microwave and I want to be at least mostly sure before I throw them in there. It's ceramic, but what kind I don't know. Does anyone have any idea if these are microwavable? Found the same set on eBay but the seller didn't seem to know much about it or if it was microwavable.