Crown was the name of a well known optician's shop in Amsterdam during the 1970's. These giant glasses were a buy at the Amsterdam flea market "Waterlooplein" during the 1980's. In most cases, putting a year of manufacturing on vintage glasses is an educated guess but in this case I'm fairly sure it was 1975. A good friend of my ex-wife had just bought a very similar pair when I first made her acquaintance. I'm not sure if Crown designed and manufactured glasses. They may well only have stamped and sold them.