The Oldest Glass on the Beach
Most people walk straight past black sea glass. It sits among the pebbles looking exactly like a pebble, dark, heavy, unremarkable. Pick it up. Hold it to the light. What was black becomes deep olive green, dark amber, sometimes a rich bottle green with bubbles trapped in the walls. That’s not a stone. That’s one of the oldest pieces of glass you’re ever likely to hold.
Black sea glass is not a colour in the way blue or red is a colour. It’s a category of very dark, heavily tinted glass made dark deliberately, to protect its contents from light that reads as black until the sun shines through it and reveals what it really is.
Why black sea glass exists
Black glass is among the oldest bottle glass ever made. It was produced by adding high concentrations of iron oxide to the melt, which darkened the glass and strengthened the walls essential for transporting wine, spirits, ale and oil on long sea voyages without the contents spoiling. Georgian gin bottles, Dutch schnapps flasks, Spanish wine bottles, rum casks, all black glass, all made to survive a crossing.
Production ran from roughly the 1500s through to the late Victorian era, when clearer glass and better manufacturing processes replaced it. The bottles that entered the sea, thrown overboard from ships, lost in wrecks, dumped from coastal settlements, have been tumbling ever since. A piece of black sea glass found on a UK beach today could be 200, 300, or in rare cases 400 years old. It is almost certainly the oldest object you will pick up on any beach walk.
The Londonderry Bottleworks at Seaham also produced black glass, and some of the earliest pieces found on the North Sea coast are thought to originate from Spanish Armada supply ships, chased up the English coastline in 1588, carrying bottles of wine and oil. Crude, bubble-filled, dark olive green. Genuinely ancient.
Best UK beach for black sea glass right now
Seaham, County Durham, both for the Londonderry Bottleworks black glass and for the extraordinary possibility of genuinely historic pieces from centuries of North Sea shipping. Black is more consistently found at Seaham than almost anywhere else in the UK.
Of course, Seaham is one of the best Seaglass beaches in the world but there are times on other beaches that can be just as good, when the swell, wind, and recent storms can make a big difference on what is being washed up, so there are times when Seaham is too sandy and there are others that are producing, thats why we make our dynamic colour leaderboards.
Other UK beaches where black has been recorded
- Boulmer, Northumberland — black recorded among finds; North Sea shipping history
- Robin Hood’s Bay, Yorkshire — occasional black, including possible shipwreck glass
- Cullen Bay, Scotland — black recorded; Scottish coastal trade routes
- Walton-on-the-Naze, Essex — black from Victorian domestic and industrial glass in the eroding Naze cliffs
Below is the best chance of finding Black Pirate Glass when conditions are perfect, good for planning trips.
What to look for
The challenge with black sea glass is that it looks like a stone. The trick is to check the weight and texture of glass, which has a smoothness and a slight translucency even when very dark, whereas a pebble is completely opaque and often rougher in texture. Pick up anything dark and smooth that gives you pause. Hold it up to the sky.
In direct sunlight, the true colour reveals itself immediately. In flat light, it’s harder because you’re relying on texture and feel. Thick, heavy, well-rounded pieces with a slightly glassy surface are the ones to examine. Bubbles in the glass are a sign of age. Older hand-blown pieces often have them trapped in the walls.
From beach to jewellery
Black sea glass set in silver is one of the most striking combinations in the collection, where dark, ancient glass against bright metal is unlike anything else. Browse the current pieces at Mermaid Tears, each one hand-hunted from a UK beach. →
Conditions change daily. Always check tide times before visiting.