Cobalt blue sits in an interesting position on the rarity scale, rarer than plain blue or aqua, but more findable than orange or grey if you’re hunting the right beaches. It has a finding ratio of roughly 1 in 250 pieces and is not often found on UK beaches.
The history behind it is excellent. In the late 1700s, cobalt blue glass was a symbol of wealth in Europe, with Bristol, England, emerging as the centre of production, where over 15 glassworks crafted striking blue tableware and decorative objects for wealthy customers, including European royal families. That’s worth noting for your guide: Bristol Blue Glass is a genuinely British origin story.
By the Victorian era, the use had shifted: cobalt and cornflower blue became the standard colour for medicine and poison bottles, with the bright hue and moulded ribbing specifically designed to warn users of dangerous contents. Not everyone was literate and could read warning labels, so bottles containing poison were given a distinct cobalt blue colour and a unique hexagonal shape so people could easily recognise them by touch in the dark. That’s a brilliant detail for the colour page a piece of cobalt blue sea glass was almost certainly once a poison bottle.
Cobalt blue sea glass most likely originated from late 1800s to early 1900s poison and medicine bottles, cosmetics jars, insulators, inkwells, decorative art glassware and perfume bottles.
The best UK beaches for cobalt blue sea glass
Seaham, County Durham Your best bet in the UK, and not just for volume. At Seaham it’s not unusual to pick up vivid cobalt blues among the usual greens and whites, thanks to the variety of glass once made there. Cobalt blue has been confirmed as a find at Seaham, where one collector described it as their standout piece of the day, noting that Seaham makes it easier to discover colours that would be genuinely exceptional anywhere else
Robin Hood’s Bay, North Yorkshire. Lucky hunters at Robin Hood’s Bay can spot the occasional deep cobalt blue or purple piece from medicine and poison bottles of long ago. The village’s Victorian history, households dumping glass over the cliffs, plus the famous 1917 bottle boat wreck, give the bay a genuinely varied mix of old glass. Cobalt won’t be common here, but it turns up.
Cullen Bay, Moray, Scotland. Keep an eye out at Cullen for what local collectors have nicknamed “Scottish sea sapphires” cobalt blue glass that often came from medicine or perfume bottles of the last century. Cullen is uncrowded, scenic, and genuinely productive for a Scottish beach, a good option if you’re north of the border.
Musselburgh, East Lothian Cobalt and cornflower blue pieces have been confirmed at Musselburgh beach in Scotland, described by visiting collectors as older, smoother and silkier than glass found elsewhere. Not a beach that gets much attention in sea glass guides, which makes it worth knowing about.
Portishead / Bristol Channel, North Somerset. Worth a mention for the history alone. The Nailsea Glassworks, just a few miles inland from this stretch of coast, operated from 1788 to 1873, and the Bristol Blue glassworks was active in the city throughout the same period.
Any cobalt that ended up in the Bristol Channel from either source has had over 150 years of tidal movement to work its way along this coastline. Finds here aren’t reliably reported, and the Bristol Channel’s muddy, sandy character makes for less well-frosted glass than you’d find further north, but if you’re in the area, it’s a beach with genuine glass heritage under its feet.
When to go
Cobalt blue is old glass, most of which dates from the Victorian and Edwardian eras. That means it’s been in the sea for well over a hundred years, and the best-conditioned pieces get churned up during winter storms. Low tide after heavy weather is your best window at any of these beaches. Spring tides around the new or full moon expose the most foreshore and bring the most material to the surface.
Today’s live conditions
have the Sea Glass Score leaderboard above to see which beaches are in peak condition right now before you set off.
If you find one
Cobalt blue sea glass makes some of the most striking jewellery of any colour. That deep, saturated blue works beautifully set in silver — the contrast is everything. At Mermaid Tears, each piece of jewellery is hand-hunted from UK beaches and handmade from the glass up. Browse the collection.
Above is the best place to find Colbalt Blue right now, and below is the best place to find Colbalt Blue in the best conditions, handy for planning a trip.