set of six 'carnival glazed' German china plates

I'm not sure what these are, I don't think I've ever seen any others like them. (I've heard of 'carnival glass' of course, but these ain't that??) They are a set of six white china plates with a gentle yellow swirled decoration around their rims, accented by narrow silver bands around the rim and middle. The centers are white with an iridescent glaze, appearing to have multiple hues depending on the light and viewing angle when seen. They are 7-3/4" across, and each has the word 'Germany' in an oval with a '7.' below it on the underside.

Would anybody have any clues to help me learn what they are, who made them, or even just whatever that kind of glaze (?) is that gives them the iridescent look? Is that some kind of coating that can go on either glass *or* china, and how does it work?? I've never known...?? I don't have any real idea of how old these are, either.