Monday, July 21, 2025

Geology of Everyday Stuff and Things: Colorful Glass and Vintage Glassware

From Estate Sale to Elements: How My Geology Obsession Helped Me Understand Glassware


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I recently, completely by accident, fell into the world of collecting old glassware. It all started when I stumbled upon some vibrant cobalt blue pieces at an estate cleanup. I thought, "These are actually kind of cool... I wonder how old they are?"

Turns out, not that old. Maybe from the 1980s.
But that simple question led me down a rabbit hole of research I never saw coming.

I used to think glassware collecting was reserved for cardigan-wearing retirees sipping chamomile tea while gossiping about the neighbor’s petunias. (Yes, I was a bit of a snarky gremlin in my ignorance.) But as I dug deeper, I realized: colored glass isn't just fancy and decorative, it’s linked to geology!

Vintage manganese glass glowing green under 365 nm ultraviolet light
Manganese Glass Glowing Under 365 nm UV Light

The Geology of Glass Colors

The more I read, the more I realized that much of the color in glass comes from natural minerals and metallic elements. Just like minerals tint natural crystals (think smoky quartz, amethyst, or citrine), those same geological "impurities" are responsible for the dazzling hues in manmade glass.

Here’s a breakdown of some common glass colors and the minerals or elements that give them life:

Blue Glass

  • Element: Cobalt

  • Mineral Sources: Cobaltite, Erythrite

  • This is the rich, deep blue you see in antique medicine bottles and art glass.

Green Glass

  • Elements: Iron, Copper, or Chromium

  • Mineral Sources: Malachite, Olivine, Chromite

  • Sometimes, green glass wasn't even meant to be green—old bottles turned green just because the sand used had iron in it.

Red Glass

  • Elements: Gold or Copper

  • Mineral Sources: Native Copper, Cuprite

  • Red glass is notoriously hard to make and often expensive due to gold content.

Purple (Sun-Purple) Glass

  • Element: Manganese

  • Mineral Sources: Rhodochrosite, Pyrolusite

  • In the 1800s, manganese was added to decolorize glass, but after decades of sunlight, it turns purple.  This has become my favorite find. 

If you're curious whether a piece of glass contains manganese, you can test it with a 365 nm UV flashlight, like the Convoy C8. Manganese glass glows green under this light, but not under the more common 395 nm UV blacklights.

Yellow Glass

  • Elements: Sulfur or Uranium

  • Mineral Sources: Realgar, Carnotite

  • Uranium glass, often called Vaseline glass, glows a bright neon green under UV (both 365 nm and 395 nm. You can find small uranium glass samples online to experiment with.

White (Opaque) Glass

  • Element: Tin Oxide

  • Mineral Source: Cassiterite

Black Glass

  • Element: Iron Oxide

  • Mineral Sources: Magnetite, Hematite

  • Often used for beer and spirits bottles due to its UV-blocking properties.

Geology Isn't Just in the Lab... It's in Your Kitchen Cabinet and Church Windows

This revelation got me thinking: glass is just another form of geology made practical. It's like human-made rock. And some of the techniques that give us modern colored glass haven’t changed much from when ancient artisans started experimenting thousands of years ago.

In fact, some of the most beautiful stained glass windows in cathedrals are still gleaming today thanks to those same earthy pigments. Geology:  frozen in time, color and light, for everyone to enjoy.

If you’re curious about identifying old glass styles and colors, a guide like Mauzy's Depression Glass: A Photographic Reference is a great resource.  For even older glass, the internet seems to be the best research tool.  

Purple manganese glass on a wooden background with a white doily
Purple Manganese Glass Under Normal Lighting

Naturally Formed Glass: Earth's Own Artistry

Nature makes its own glass too, without any help from humans:

Obsidian

Volcanic glass formed when lava cools too quickly for crystals to form. Usually black, but can be brown, green, or even iridescent depending on trace elements.

Tektites

Formed when a meteorite slams into Earth with enough force to melt terrestrial rock. These glassy spherules often land far from the impact and are usually black or olive green.

Fulgurites

Glass tubes formed when lightning strikes sandy ground. They're often gray or translucent, and they look like fossilized lightning bolts.

If you ever want to investigate these kinds of minerals or even the sand around you, a rock and mineral testing kit is a surprisingly fun (and kind of addicting) beginner tool to have, and a great way for the whole family to learn about geology. You can pair it with a classic geologist's loupe to inspect inclusions and fine crystal structures in both minerals and glass.

Still Learning, Still Obsessed

Glassmaking might have started in Mesopotamia around 3500 BCE, but I feel like it’ll take me another few thousand years to wrap my head around all of it. I’ve only just started this journey, but it’s already connecting things I love: science, history, and the Earth itself.

So next time you hold a colorful piece of old glass, remember... it’s not just a pretty object. It’s shaped by human curiosity, made possible because of geology.

Want to Go Deeper? Here Are Some Beginner-Friendly Finds

Whether you’re diving into the world of vintage glass or exploring the rocks and minerals that color it, these fun finds are a perfect place to start:


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