There is one beach in the world where the sea gives up pieces of glass that look like nothing else that has ever existed. This is about that beach, and those pieces.
Somewhere on a beach in County Durham, right now, the North Sea is washing something extraordinary onto the shore.
A piece of glass that’s swirled with two colours, or three, or four, cobalt blue twisted through amber, green bleeding into white, a ribbon of red running through dark olive. Each one is completely unique. Each one the product of a single moment in a Victorian factory, over a hundred years ago, that was never repeated and can never be replicated.
Seaham multis. End-of-day glass. The holy grail of UK sea glass hunting.
If you’ve never heard of them, you’re about to understand why serious collectors travel from the United States, from Japan, from Australia, to stand on a stretch of Durham coastline and search the tideline in all weathers.
What are Seaham multis?
Seaham multis are multicoloured sea glass pieces unique to Seaham in County Durham, swirled, streaked or layered with two or more distinct colours of glass fused together during manufacture.
They come from a specific place, a specific factory, and a specific practice that ended over a century ago.
The Londonderry Bottleworks operated in Seaham from 1853 until 1921. At its peak, it was one of the most productive bottle factories in Britain, turning out millions of bottles a year for the beer, wine, medicine and chemical industries.
At the end of each working day, the glassblowers faced a practical problem. The furnaces couldn’t simply be switched off the molten glass had to go somewhere. Different colours of glass had been used throughout the day for different orders: the cobalt blue runs, the olive green batches, the amber production, and the clear glass. At the close of the shift, the leftover molten glass from different runs was combined and poured together.
The result was glass that nobody intended to make. Swirls of colour that happened because of physics and temperature rather than design. Blues and greens bleeding together. Ambers and clears folding through each other. The occasional extraordinary piece where three or four colours met at just the right moment and froze in place as the glass cooled.
These pieces were never meant to be beautiful. They were a waste. The factory discarded them directly into the sea at Seaham, as was standard practice for industrial waste in the Victorian era.
The North Sea has spent a hundred years turning them into what washes up today.
Why are they unique to Seaham?
This is the question that matters, because the answer is what makes Seaham multis genuinely irreplaceable rather than just rare.
Several factors aligned at Seaham that don’t exist anywhere else:
The specific factory practice. The end-of-day mixing of multiple glass colours in the same pour was a Londonderry Bottleworks practice. Not every glass factory disposed of waste this way. The combination of different coloured runs, poured together rather than separately, is what created the multicoloured result.
The direct sea disposal. The factory’s location right on the coast meant waste glass went directly into the North Sea rather than being carted to landfill or broken up. This is what put the glass in the sea in the first place.
The North Sea itself. The particular conditions of the Durham coast, the wave energy, the tidal patterns, and the pebble composition of the beach have been ideal for frosting and rounding glass over the decades. The same glass disposed of into calmer waters might never have developed the quality of frosting that makes Seaham multis what they are.
The factory closed in 1921. This matters enormously. The source stopped over a hundred years ago. No new multis are being created. What’s in the sea now is all there will ever be, and the supply is finite, reduced by every piece that’s ever been collected.
You cannot find Seaham multis anywhere else in the world because no equivalent factory operated in an equivalent way in an equivalent location. They are the only sea glass of their kind on the planet.
What do Seaham multis look like?
The variety is what makes them extraordinary. No two pieces are the same, not approximately the same, not similar, actually completely different because each one was created by a unique pour of uniquely proportioned mixed glass.
The most common combinations involve:
Cobalt blue and clear or white – one of the most striking. The vivid blue bleeding through or alongside frosted white, sometimes in clean bands, sometimes in organic swirls.
Green and amber – the two most common base colours from the factory’s regular production, combined in pieces that range from subtly two-toned to dramatically streaked.
Multi-colour pieces – three or four colours in a single piece. These are the most extraordinary finds and the most sought-after. A piece with cobalt, amber, green and white swirled together is almost impossibly beautiful.
Red inclusions – occasional pieces contain a streak or thread of red glass. These are extremely rare even among multis, because red glass production was limited and its presence in end-of-day pours was therefore uncommon.
The frosting on well-aged Seaham multis has a particular quality. A hundred years in the North Sea produces a depth of pitting and a completeness of frosting that no recently tumbled glass can replicate. The surface feels ancient because it is ancient.
Size varies considerably. Most pieces are thumbnail-sized or smaller – the tumbling process naturally reduces size over decades. Larger pieces, anything over two centimetres, are exceptional and command serious collector interest.
How do you find them?
Seaham beach is the only place in the world where Seaham multis wash up, which means if you want them, there’s only one destination.
The beach at Seaham has been hunted intensively for decades, which means the easy finds are long gone. Finding multis today requires:
Timing. The best hunting is in the hours immediately after high tide when fresh material has been washed in. Early morning, before other hunters arrive, gives you the best access to a freshly washed beach.
Conditions. Seaham produces better after storms. Significant North Sea weather turns over buried material and brings pieces to the surface that have been hidden for years. Checking the Sea Glass Score before a trip tells you which conditions are most favourable.
Patience and slowness. Multis are often small. The temptation on any productive beach is to cover ground. At Seaham, you need to slow right down and look carefully at a smaller area. Experienced hunters work methodically rather than roaming.
The rocks. The rocky sections at the north end of the beach where glass gets trapped in crevices rewards careful searching. These areas are less accessible and therefore less thoroughly hunted than the open beach.
Going further. The beaches immediately north and south of Seaham Nose’s Point, in particular, receive the same glass from the same source and are hunted less intensively. Worth including on any Seaham trip.
The other glass at Seaham
Multis are the headline act but Seaham produces extraordinary glass beyond them.
Pirate glass – the dark, iron-rich glass of the 17th and 18th century — washes up here alongside Victorian and Edwardian material, reflecting the depth of the maritime history on this stretch of coastline.
Thick Victorian glass – cobalt blue, amber, deep green in chunky, well-frosted pieces from the bottleworks’ regular production. The quality of the frosting on Seaham glass is generally higher than most UK beaches simply because of the age of the material.
Pottery shards – not sea glass strictly speaking, but Seaham also produces beautiful old pottery fragments, sometimes with visible patterns. Worth collecting alongside the glass.
What are Seaham multis worth?
Genuinely good Seaham multis are among the most commercially valuable sea glass pieces found anywhere in the world.
Small but well-frosted two-colour pieces sell for several pounds each from knowledgeable buyers. Three-colour pieces command significantly more. Large, well-frosted multi-coloured pieces, anything over two centimetres with three or more distinct colours, can sell for tens of pounds from serious collectors, particularly in overseas markets where the glass simply isn’t available at any price.
American sea glass collectors in particular have an extraordinary appetite for Seaham material. There is no equivalent in the United States. Pieces that a UK hunter might consider a good but not exceptional find can generate real excitement from buyers who’ve never had access to this type of glass.
For jewellery, Seaham multis present a unique challenge and opportunity. Each piece is completely unique, which means every piece of jewellery made from one is also unique in a way that no other material can claim. The story of the Londonderry Bottleworks, the end-of-day pour, the hundred years in the North Sea that narrative adds value that conventional gemstones simply don’t have.
The Mermaid Tears collection includes Seaham glass, and the story behind each piece is part of what makes it worth owning. A pendant made from a Seaham multi isn’t just jewellery. It’s a physical piece of industrial history that the North Sea spent a century making beautiful.
Going to Seaham
If you’re planning a trip, a few things are worth knowing:
The beach is at the bottom of a cliff path from the town. Parking is available near the harbour. The walk down is straightforward but worth remembering on the way back up when your pockets are full of glass.
Go at low tide. Check the tides before you leave and plan to arrive as the tide is going out, giving you the maximum exposed beach time as it drops.
Go after storms. A calm week of settled weather produces fewer new finds than a day after North Sea swells have been working the beach.
Go early. The beach gets busy on weekends, and good finds don’t wait.
And go with realistic expectations. The beach has been hunted for decades. You may find multis on your first visit, or you may find good single-colour pieces and come home knowing you need to go back. Both are worth it.
Seaham isn’t just the best sea glass beach in the UK. It’s one of the most extraordinary beachcombing destinations in the world.
The North Sea has been keeping its secrets there for a very long time.
Planning a trip to Seaham? Read the full Seaham beach guide for everything you need to know. Check current conditions on the Sea Glass Score before you go. And if you find something too beautiful not to wear, Mermaid Tears makes jewellery from Seaham glass.
