The Truth about Pirate Glass

By Kirsti Scott

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Yo ho, yo ho, a pirate’s life for me! Every time I find an almost-black piece of “pirate glass,” that song pops into my head. But despite the fun name, that dark-colored shard is likely not actual glass from a pirate, though it could have a long history.

Backlit black glass (Barbara Smith).

Most of the black sea glass that we find is not actually black, but instead is an intense shade of a color—such as green, brown, purple, blue, or red—that is so dark that the glass appears black. The black color was often created by adding minerals to the glass mix during manufacture, such as copper oxide (for green and turquoise blue), iron oxide (for green, blue, and yellow), and cobalt oxide (for light and dark blue). Some glassmakers added coal and wood ash or iron slag during production.

Dark-colored glass bottles have a few important properties that have made them useful throughout history. These additives made for darker, stronger glass. Dark glass better protects liquids, including alcohol, from the damaging effects of sunlight, especially in the days before refrigeration. This is why most beer and wine bottles still come in amber and green bottles. Darker glass is also stronger, which protects the bottle from breaking through rough handling during transportation and storage. Perfect for pirates on seafaring ships!

Victorian French black glass button (Adrian Parker). Case gin bottle (Wiesy Lauffer). Vitrite insulator (Kirsti Scott).

Some glass was intentionally colored to look black, including black glass made in Venice in the 16th century, decorative glassware in the color called “Black Amethyst” made in the early 20th century, 19th-century case gin bottles in a dark olive color, and glass created to resemble the organic mineral “jet” that was used in jewelry and buttons. Other black glass was created for industrial uses, such as electrical line insulators and the purple-tinted black glass for lightbulb insulators made using manganese oxide by the Vitrite Company in Ohio. Bars or nuggets used in glassmaking to colorize clear glass appear black, and these wash up on beaches near old glassmaking factories, such as Seaham, England. Alas, very few of these decorative and industrial items were used by pirates.

Glassmaking color nuggets from Seaham (Kirsti Scott). Antique bottle bottom (Barbara Smith).

The bottles that actual pirates used in the Golden Age of Piracy (between the 1650s and the 1730s) would have been handblown, so you can check the age of your beach glass piece by looking to see if there are bubbles and imperfections in the glass. Thicker and uneven bottle walls are another indication of an older, handmade bottle. Maritime piracy was at its peak in the Caribbean, the United Kingdom, the Indian Ocean, North America, and West Africa in the late 17th and early 18th centuries. If you want to find actual pirate glass, you’ll need to visit beaches near the shipping lanes and harbors that were most active during that time period: Bermuda, Jamaica, and Tortuga; other trade ports in the Caribbean and Eastern Pacific; the Indian Ocean and Red Sea; and other locations where valuable cargoes were loaded and unloaded to be shipped to Europe over the vast oceans.

Can you spot the black glass? Fife, Scotland (Kirsti Scott). Dark green glass, Cork, Ireland (Kirsti Scott). Dark brown glass, Curaçao, Dutch Caribbean (Kirsti Scott).

While “black” glass is relatively common, it’s not always easy to spot it on the beach, making it a relatively rare color of sea glass. Dark glass tends to blend in with rocks and pebbles on the beach. One way to distinguish glass from stones is to find a spot where the water is drying up and look for the pieces that are still wet, as glass often dries more slowly than porous rocks. Another sign is to search for the pitted surface of beach glass, which sometimes looks different from that of surrounding rocks. And maybe just a hint of a color on the edges will help you pick out a piece of glass. Of course, black glass is easier to spot on a white, sandy beach than on a rocky shore. The only way to find out if it’s glass is to pick up the piece and see if light shines through.

Even if no pirates ever drank from the bottle that created your sea glass shard, it’s a rare find, a great addition to your beach glass collection, and a great piece of history. And, it’s still fun to call it “pirate glass.”

Learn more about black sea glass ›

View Caribbean glass from the collection of Wiesy Lauffer

This article appeared in the Beachcombing Magazine January/February 2023 issue.