Atomic Razor Blade (ca. 1947 to 1955)
I know very little about these "Atomic Razor Blades" other than what can be read on the back of the envelope. Knoxville, Tennessee is where they were manufactured, and Knoxville is 20 miles downwind from the "Atomic City" of Oak Ridge.
The earliest of the assigned dates (ca. 1947) is based on the fact that the label illustrates atomic testing in the Pacific. The last assigned date (ca. 1955) is based on the fact that I have found advertisements for these Atomic Razor Blades dating from 1950 to 1953 (Kingsport Times).