Depression glass appears green, particularly a rich, glowing green, primarily due to the inclusion of uranium in its composition during manufacturing. This gives certain pieces of green Depression glass their unique luminous quality.
The Science Behind the Green Glow
The distinctive green color and the characteristic glow of some Depression glass pieces are directly linked to a specific element: uranium.
- Uranium Content: If the glass glows a rich green color, it contains uranium. Manufacturers during the Depression era sometimes added small amounts of uranium oxide to the glass mixture to achieve certain colors and effects.
- Green Fluorescence: This green appearance is due to a phenomenon called fluorescence. When exposed to ultraviolet (UV) light (like that from a black light or even natural sunlight), the uranium in the glass absorbs the UV energy and re-emits it as visible green light, causing the glass to glow.
- Lighting Variability: The perceived color of uranium glass can change depending on the light source. For instance, an example of Vaseline glass, a specific type of uranium glass, might look yellow under incandescent lighting but take on a greenish tinge when viewed outdoors due to the natural UV radiation present in sunlight. It is important to note that there are exceptions to these typical appearances and reactions.
Key Characteristics of Green Uranium Glass
This table summarizes the main points regarding green Depression glass containing uranium:
| Characteristic | Description |
|---|---|
| Primary Cause | The presence of uranium (typically uranium oxide) in the glass formula. |
| Visual Effect | Produces a rich, vibrant green hue that famously exhibits fluorescence, glowing brightly under ultraviolet (black) light. |
| Lighting Impact | Colors can shift; for example, Vaseline glass (a subset of uranium glass) may appear yellow indoors but gain a noticeable greenish tinge when exposed to natural light outdoors. |
| Variations | While uranium is the definitive cause for the glowing green effect, there are exceptions in how glass might appear or react, meaning not all green glass contains uranium, nor does all uranium glass look identically green in all conditions. |
Identifying Uranium Glass
Collectors often use a UV (black) light to confirm the presence of uranium in glass. A strong, vibrant green glow is the tell-tale sign of uranium content. Pieces containing uranium are often referred to as "Vaseline glass" when they are a translucent yellow-green, or more broadly as "uranium glass."
