Sea Glass

Image: Seapig

Sea glass is naturally weathered glass, having the appearance of tumbled stones, with smooth edges and a frosted appearance. It is also known as drift glass, from the process of longshore drift that wears it. It may take 20-40 years, sometimes as much as 100-200 years, to take on its characteristic appearance.

Where does it come from?

Sea glass starts off just like any other shard of glass; broken, jagged and sharp. The travels of any one piece of sea glass have been long and tumultuous since it entered the sea, tumbled by the ocean and scoured by sands and stones. How any one piece got to the beach is a mystery, but there are some common routes by which many pieces wash up on your beach. The most common are as flotsam from shipwrecks and jetsam from sailing vessels. In some countries, where there is no waste infrastructure, general rubbish may discarded into rivers or the sea. You might even find a piece of a message in a bottle that didn’t make it in one piece.

Many years ago glass factories dumped their glass waste into the sea. An example of this is Seaham, a harbour town on the Durham Heritage Coast. Seaham is world-famous for its abundance of unique sea glass, making it a ‘must-see’ site for collectors. Seaham and nearby Sunderland were home to many bottleworks and glass-making factories during the Victorian and Edwardian eras, and Seaham boasted the largest glass bottle works in Britain – The Londonderry Bottleworks, operating from the 1850s to 1921. 

The bottleworks produced up to 20,000 hand-blown bottles every day, in different colours and designs including hand crafted bottles, perfume bottles and household glass, all of which were distributed across the globe. 

Londonderry Bottleworks (Image: East Durham Now and Then)
Seaham sea glass – no two pieces are the same. Treasures include codd marbles, used as a seal for fizzy drinks, safety glass with wire reinforcement running through it, bottle necks and sea pottery! 

What about colour?

Sea glass has comes in many colours, depending on the type of glass it was made from. Different shades are determined by the chemicals used in making the glass, the temperate of the melt and the length of time it was melted for. Each colour tells us a little about a nugget’s past. Colour rarity varies from country to country, but globally white is the most common and orange the rarest. The most common colours in the UK include white and green.

White sea glass, from colourless bottles, could have been an old milk bottle, a vase or jug, or even an old car windscreen.

Sea glass comes in many shades of green. Very dark green, almost black in colour, may have come from bottles holding alcohol. The original Coca-Cola bottles came in pale green. Some olive oil brands still use iolive-coloured glass, just as it they many years ago. Bright emerald green was sometimes used for medicine or mineral bottles , and various shades of green were used for fishing buoys. if you find a mermaid’s nipple it has come from a fishing buoy (no mermaids were harmed in the making of these).

Some of the rarest & most treasured sea glass finds, nipples & pikos (navels) are the inside nubbins or outside blob seals from glass fishing floats (Image: Dr Beachcomb TM)

An increasingly rare green sea glass is uranium glass. This had uranium (usually in the form of one of its oxides) added to the mix before melting. The amount of uranium varied from a trace to around 2% (some early pieces may have had higher levels). Uranium was added to decorative tableware and ornaments for its fluorescent effect under UV light. The production of uranium glass dropped dramatically from the 1940s, when supplies of uranium were diverted towards the manufacture of nuclear weapons or nuclear power. The yellowish green uranium glass was sometimes called Vaseline glass, due to its perceived resemblance to the colour of petroleum jelly.

Uranium glass, in daylight and under UV light (Image: Aritra Roy)

Cobalt glass includes a cobalt oxide or carbonate compound in the mix to produce the typical rich blue colour. Cobalt glass was traditionally used for apothecary poison bottles. Other uses include glasses for professional olive oil tasters to hide the colour of the oil, and for flame testing in chemistry labs. Bristol blue glass is popular with collectors – used for Harvey’s Bristol Cream sherry and Tŷ Nant mineral water.

Black sea glass, hard to distinguish from the shingle, isn’t actually black; if you hold it up to the light, you will see shades of either brown or green. Hundreds of years ago, very dark, thick glass was needed to keep the sunlight from spoiling alcohol such as rum, gin and beer.

Rarer colours like red, orange and yellow are highly sought after by collectors (see rarity chart below). Red may have been used for maritime lights or fancy tableware. Bright orange sea glass is very rare. It may have come from old lanterns, carnival glass or the taillights of old motor vehicles. Sea glass can also be found in pink and lavender. These are also rare colours now, but once were cheap and cheerful tableware.

Sea glass rarity chart from the US reading from L to R, top to bottom (Image: West Coast Sea Glass)

What about size?

Just like pebbles, sea glass pieces carried along the coastline and are subjected to sorting. This is where the ocean’s currents and tides sort the pebbles by size and shape, depositing them on the beach in a specific order. The process of winnowing is the natural removal of fine material from coarser material (larger pieces) by wind or flowing water. Once a sediment – including pieces of sea glass – has been deposited, subsequent changes in the speed or direction of wind or water flowing over it can agitate the grains and allow removal of the finer pieces.

I am obviously looking in the wrong place, as I only ever find the tiniest pieces of sea glass. Well done to our keen observers who have been sharing their sea glass finds on Rye Bay Beachcombing recently.