420 Science UV Screw Top Stash Jar - THC Write & Erase (Med) Pressed Glass - Made in Europe. Permanent, Baked on Glass Decals Holds: 1/4 oz herb, 3.4 fl. oz. Width: 2.5 in. The brand new UV 420 Jars are here. As we all know, sunlight enables plants to grow. But if they continue to be exposed to the sun after reaching maturity, the effect of the light actually accelerates the molecular decaying process. However, violet glass works as a natural filter that protects the quality of sensitive plantlife. These new 420 Jars block all UV-B rays and the complete spectrum of visible light with the exception of violet. At the same time, they allow permeation of UV-A and infrared light. This unique combination offers optimal protection against the aging process, thus lengthening the lifespan and potency of your herb.