VASELINE GLASS ARTICLE provided by the Vaseline Glass Collectors, Inc. website

Vaseline Glass was primarily made from 1840, up to just before WWII,  and then was continued from 1959 to the present.  Current manufacturers include: Fenton Glass and Mosser Glass, as well as some small independent shops such as Gibson Glass and Jack Loranger (HotGlass.cc). Vaseline Glass was in its' heyday during the Victorian period from the 1880's to the 1920's. The yellow-green glass did not sell as well as other colors of glass, so during the depression years, glass manufacturers started adding more iron oxide (commonly known as RUST) to the glass mixture (but still included the Uranium Dioxide) and this had the effect of making the glass more green. Because of this, most green depression glass will glow.  The government confiscated all supplies of uranium during WWII and halted all production of Vaseline Glass from approximately 1943 until the ban was lifted in Nov. 1958.
Only after years of testing by the various regulatory departments of the government were glass companies once again allowed to make this glass.  In Victorian times, glassblowers who made Vaseline Glass usually died at a relatively young age of lung cancer, and the 'stories' have persisted for years that this was due to their exposure to molten Vaseline Glass. However, when this information was discussed with different experts on radiation (from University of Missouri and University of Oklahoma), they felt that there may have been other reasons for their early demise, as radiation tends to affect the thyroid glands the most.  I guess this will also be a subject for long debate.
Due to the tight regulations on Uranium Dioxide and the expense of this ingredient, only very limited quantities are being produced today. Due to this, most collectors are aware of the limited nature of its' production and this is reflected in the marketplace.
Vaseline Glass Collectors, Inc., (VGCI), is a non-profit 501(c)3 organization incorporated in 1998 to educate and unify Vaseline Glass collectors everywhere! There are different definitions of what is or is not "vaseline glass," depending on what part of the world you are located. Our organization uses this definition: Vaseline Glass is a particular color of yellow-green glass that is made by adding 2% Uranium Dioxide to the ingredients when the glass formula is made. The addition of the Uranium Dioxide makes the glass color yellow-green. Vaseline Glass is ALWAYSverifiable by using an ultraviolet light (blacklight) on the glass item. When this is done, the glass turns a bright florescent green! Sometimes, even the most trained eye can be fooled by a piece of glass that looks like Vaseline Glass, but will not 'glow' or fluoresce bright green under a blacklight. Not all yellow-green glass will turn florescent GREEN when a UV light is shined on it. When manganese is added to the glass formula (which also makes a yellow-colored glass) instead of Uranium Dioxide, for instance, the end product will glow under a black light, but the color is an orange/peach color OR a lime green color that is much fainter than the bright neon green under UV light. Manganese was added to the glass mixture to counteract the minor traces of iron that would give the glass a  'coke-bottle' greenish tint to it.