That’s all on the underside, like cut glass. Only here it’s pressed underneath. The top of the plate itself is smooth. This is anchor hocking “bubble” pattern. Produced from 1934 to 1965. This is “Sapphire blue“ a very pale blue, which mostly shows up when the plates are stacked.I don't get this. Is it actually a plate that someone would eat from...with all those lumps on it?

Oh these plates, I have 4, are from waaay back when mom and I went to garage sales and flea mkts…the 70s dare I say. And by far the best place I find today are hospital or cancer type thrift stores. They seem to get high quality donations.Well…the American obesity issue (guilty as charged) clearly indicates that plate size change.
Plus the decades-long reality of NOT using plates at all, but simply eating fast food out of bags and paper wrappers can’t have helped.
You must have great thrift stores there. The ones around me are mostly plastic trashy stuff. Plus after last year’s horrific hurricane flooded thousands of homes, the source for donated items is very low.