Siliceous skeletons & the origin of clear glass windows

Glass

I enjoy microfiction prompts, and lately I've written a couple of stories about Surzi (keep an eye out for Wednesday's šŸ‘€) , an enchanted beast that lives in a magic desert rife with a substance called aetherglass. I figured it was as good a time as any to learn more about how glass actually works.

Fun Facts

  • The glass trade (along with metal and ivory) was at least partially responsible for the rise port cities in the Levant around 1200 CCE.
  • Volcanic glass (obsidian) was one of earliest known trade goods in the Neolithic Near East thanks to its rarity and ability to hold a sharp edge.
  • Glass jewelry was common during the late Roman period; as an example, Jewish funerary offerings often included glass bracelets with menorah decorations.
  • Indigenous prisoners on the Australian island of Rottnest made spearheads out of glass in the 19th century.
  • Some microscopic algae and sea sponges have skeletons made out of what is technically a form of natural glass.

Natural Forms

Glass is created when a molten material cools so fast it can't form crystals; they're sort of frozen between normal liquid and solid states. Obsidian is formed when molten rock cools quickly, like when lava hits the ocean. When lightning strikes a sandy beach, it creates brittle tubes of melted sand called fulgurites. When meteorites strike deserts, they can create glassy rocks called tektites.

Transition Times

The earliest glass we know of was decorative; mostly small beads and pendants dating from as far back as 3,000 BCE. The first manmande glass we know of comes from the 15th century BCE. Blown glass windows (and drinking vessels) seem to have originated in the 1st century AD, which is also around the time that glassblowers stopped coloring glass with strong, bright colors and switched to making clear glass. You can read more about this in these highly technical papers tracing the history of Mediterranean glassmaking.

Unexpected Places

Scientists only recently confirmed that independent glassmaking occurred in Nigeria; we know shockingly little about sub-Saharan glass. In a similar vein, scientists only recently discovered 2,000 year old evidence of glassmaking in Poland; they used to think glass didn't make its way there until the Medieval era. The main evidence they're using in both locations seems to be broken beads, crucibles, and cisterns for water.

Crystal Clear

The Romans prized clear "Alexandrian" glass from Egypt more than the transparent glass made in the Levant because it was perfectly clear. The sand itself available along the Southeastern coast of the Mediterranean is great for making glass because it has the right amount of lime, but in the Levant, glassmakers used manganese to get clear glass, while Egyptian glassmakers used antimony, which provided superior clarity. Click to read more about how scientists figured out how to tell the difference.


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