June 7, 2024 Melissa Marro

Why does it Glow? More than just Uranium Glass, Clear Glass Can Glow Under Blacklight Too!

Have you ever wondered why certain types of glass glow under blacklight? Let's explore the science behind this fascinating phenomenon.

What is Manganese Glass?

Manganese glass is a type of glass that contains manganese dioxide as a colorant. When exposed to ultraviolet (UV) light, such as blacklight, the manganese in the glass absorbs the UV radiation and then emits visible light, creating a glowing effect.

What is Cadmium Glass?

Cadmium glass, on the other hand, contains cadmium sulfide as a colorant. Similar to manganese glass, cadmium glass also glows under blacklight due to the presence of cadmium, which reacts to the UV light by emitting visible light.

Is Glowing Glass More Valuable?

While glowing glass may seem like a novelty, it can actually be more valuable to collectors. The unique glowing effect under blacklight adds an extra layer of intrigue and desirability to certain glass pieces, making them more sought after in the market.

How to turn Manganese Glass Purple

Next time you come across a piece of glass that glows under blacklight, you'll know the science behind this captivating phenomenon.

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Comments

Marvin Ashe - April 21, 2026
I am a member of the American Brilliant Glass Association and a Museum member of Corelle Glass Museum and here is the facts that you miss in your research that needs some corrections.
The hard differences between calling it Uranium and Manganese is this…
Fluoresces green
Responds best to 365nm
Glow can be:
bright green
soft green
yellow-green
Radiation is low but real
Documented in clear, straw, yellow, and green glass

Manganese glass
Fluoresces yellow, orange, or weak greenish haze
Often looks milky or washed
Reacts inconsistently to UV
No radiation
Used primarily as a decolorizer, not a feature

Key point:
Manganese does not produce the same crisp green fluorescence uranium does under proper 365nm UV.

Clear uranium glass:
Was intentionally produced
Is cataloged Historically
Exists in museum collections
Is acknowledged by real collectors and historians

If it were all manganese:
Museums would’ve corrected it decades ago
Collectors would’ve noticed
Geiger counters wouldn’t register anything Yet they do — even if low.
“It’s manganese” is not a magic debunk

Manganese exists, but it does not automatically replace uranium just because the glass is clear.
People say “it’s manganese” because:
They learned one fact
They now apply it to everything
It sounds authoritative on YouTube Shorts
That’s not expertise — that’s pattern abuse.
Bottom line

Clear uranium glass exists.
It always has.
The factual reality (no opinions here)
Yes — clear uranium glass exists
It has existed since the late 1800s.
It was produced by:
Czech / Bohemian glasshouses
British pressed glass manufacturers
American makers (Heisey, Fostoria, Cambridge-era blends)
The uranium content was used as a refining agent to improve clarity and brilliance to create very pale straw / near-clear glass
Under normal light the glass appears clear, water-clear, or faint champagne
Under 365nm UV the glass glows green (often softer than Vaseline glass)
This is not controversial among real collectors.
There absolutely is clear uranium glass, and this isn’t debatable, speculative, or niche. It’s well-documented, historically verified, and common in certain periods. The problem is social-media “research,” not reality.

Dave Vojacek - April 21, 2026
Just a tip. To see the fluorescence of clear glass better, especially for the video camera, put something black behind the glass such as a piece of carpet or construction paper. It will cut down on the glare and you will be able to see the fluoresceing colors better. I do this for my displays so the colors really pop. Try it. You will be amazed at the difference.