A guide to identifying beachcombing treasures

There are few pleasures quite like a slow walk along the strand line after a high tide, eyes down, watching for the glint of something special. Beachcombing is a gentle hobby that rewards patience and a keen eye – and it connects us to the sea, to maritime history, and even to our gardens. But before you fill your pockets, it pays to know what you are picking up. Here is how to recognise the most common treasures, and when to leave them be.

Reading the tideline: where and when to look

The best finds appear after stormy weather and spring tides, when the sea has churned up the seabed and deposited fresh material along the shore. Head out as the tide is receding, and focus on the strand line – the ribbon of seaweed, shells and debris left at the high-water mark. Gravelly beaches and coves with a history of shipping or fishing often yield the richest pickings. Take a cloth bag rather than plastic, and wear gloves if you are rummaging through broken shells or potentially sharp metal.

Sea glass: the frosted gems of the shore

Sea glass begins as broken bottles, windows or pottery that has been tumbled by waves and sand for decades. Genuine sea glass is frosted, with rounded edges and a smooth, matte surface. If it still looks shiny and sharp, it has not been in the sea long enough – leave it for another year or two. Common colours are white, green and brown, while blues, reds and yellows are rarer and more prized. Hold a piece up to the light to check for internal cracks or bubbles, which can indicate recent breakage. Sea glass is safe to collect and makes lovely jewellery or garden mosaic. Do not take glass from protected sites or areas where collecting is banned.

Mermaid's purses and egg cases: handle with care

Mermaid's purses are the empty egg cases of skates and rays, and sometimes of whelks. Skate egg cases are rectangular with four long horns at the corners, often black or dark brown and leathery when dry. Whelk egg cases look like clusters of small, papery capsules. A fresh egg case may still contain a developing embryo – if it is soft, slimy or has a visible yolk, return it to the water immediately. Only collect cases that are dry, brittle and clearly empty. Citizen science projects record finds, but you do not need to report anything to enjoy hunting for them. Remember: living creatures, including the small crabs and anemones that sometimes shelter inside, must be left where they are.

Cuttlefish bones: chalky treasures with a garden use

Cuttlefish bones are the internal shells of cuttlefish, which are molluscs related to squid and octopus. They wash up in their thousands, especially in autumn and winter. Look for a white, oval, chalky object with a thin, brittle edge and a feather-like pattern on one side. They are light as a feather and snap easily. If you find one that is still pinkish or has a fishy smell, it is fresh – give it a rinse and leave it in the sun to dry. In the garden, crushed cuttlefish bone is a valuable source of calcium for birds, and can be added to compost to sweeten acidic soil. Always check for tiny inhabitants before taking it home.

Driftwood and maritime heritage: wood with a story

Driftwood is any wood that has been carried by the sea. Good pieces are smooth, grey or silver, and free of bark. They may be riddled with shipworm holes, which add character. Driftwood is wonderful for garden structures, from rustic obelisks to raised bed edging, but it is salty. Soak it in fresh water for a few days before using it near plants, or seal it if you want it to last. Be mindful of maritime heritage: never take wood from a protected wreck site, and if you find something that looks like part of a ship, an old tool or a piece of pottery with markings, report it to your local museum or the Receiver of Wreck. Some items are legally protected.

Leave living creatures where they are

The golden rule of beachcombing is simple: if it is alive, leave it. That means returning:

• crabs, starfish and anemones to the pool or rock you found them on;
• seaweed still attached to rocks – it will not survive if torn away;
• any shellfish with an occupant, and mermaid's purses that still feel soft or heavy.

Do not prise limpets from rocks or move stones in rock pools – you may crush hidden life. If you find a mermaid's purse with an embryo, or a cuttlefish bone with a tiny creature inside, put it back. Collecting empty shells, sea glass and driftwood is generally fine, but check local bye-laws, especially in nature reserves and Sites of Special Scientific Interest. Take only a little, and leave the shore as you found it.