5 stackable ashtrays Maru designer Isamu Kenmochi Japan Space age 60s

Very nice set of 5 ashtrays, named maru, by japanese designer isamu kenmochi (1912 -1971). They probably date from the 60s with an aesthetic characteristic of the "space age design" movement. They are stackable, identical in shape but in different colors (orange, primary yellow, blue, black, khaki green). They are encircled with chromed metal and their body is made of melamine. Unlike other editions made in the 80s in the united states, these were made in japan: there is a stamp underneath, and some still have the label "japan". The stamp also indicates "pat pend", which would mean "patent pending", I.e. A patent application is pending. So we can think that this is one of the first editions, but I do not have enough knowledge in this area to be affirmative. They are in good condition for their age, they do not seem to have been used, but still show small signs of their age: a slight stake (on the blue ashtray, a little more than on the others) and some small marks and light scratches on the chrome. In addition, in the notch to put a cigarette, melamine has small gaps of the shiny colored layer (probably an original defect because it appears on the 5 ashtrays). They measure 7 cm in diameter, 3 cm in height. The whole weighs a little less than 500g.