This Turquoise water bottle is an older example, probably from the late 40’s or early 50’s. How do I “know” this? Turquoise water bottles were made from 1938 to 1951. They were made again starting in 1959. Water bottles from 1959 and beyond have necks that are more vertical, look at the water bottles listed with the Blenko logo etched from 1958 through 1960. They all have more vertical necks. So, this is probably 1951 or earlier. I am not sure exactly when the change happened. At some point I will take the time to try to pinpoint it a little more closely.