The Thames: Another tide, another secret

Clay pipes, pilgrims' badges ... fragments of history wash up every day on the banks of the Thames. Tim Blake digs deep

I was seven when I dragged my father down to the river to search for gold. In my young mind it was a natural place to look: the Thames was part of the sea; the sea equalled pirates, and pirates meant treasure. We stopped on Hammersmith Bridge and looked through the railings, and my dad, sensing the inevitable disappointment at the adventure's end, said: "Tim, it's very unlikely we will ever find anything."

He was wrong. Within two hours we had a found a purse. It had probably been stolen - the wallet was missing - but inside was a gold necklace. Sure, it was a tacky 9-carat necklace with a few lucky charms, but it was gold and confirmation of all my childhood beliefs.

I hadn't thought about that adventure till recently when I pulled a white gold wedding ring from the mud down by Tower Bridge: 18-carat this time. That day I also found 15 polished garnets (semi-precious gemstones), a few medieval pins and possibly a pilgrim's pewter badge.

Mudlarking is archaeology for everyone. It's your history, and you get to keep it. Pick a low tide and a good spot and you will find treasure - maybe not gold and gems, but certainly pieces of our capital's past for you to take home. There are two types of mudlarker, the professional and the amateur. The pros tend to work the shore on the low tides on weekdays. You'll see them with metal detectors and spades digging frantically before an incoming tide. They have special licences from the Port of London Authority which let them dig the foreshore (you're not allowed to dig otherwise). They sell their finds to professional dealers.

The amateurs tend to comb the shore on the weekends looking for surface finds. The two groups do not to mix much. I'm in the latter group, on the look-out for something interesting, as opposed to valuable. I don't dig because I believe that the river churns up the mud enough to keep new finds surfacing. My equipment is a good pair of boots, warm clothing and a few matchboxes and small tins to put my finds in. I own a tide table, but most papers have the high and low water times in the weather sections.

The trick to mudlarking is "getting your eye in". Get down to the shore when the tide is on the ebb and the light is good and start poking around. The first thing you might notice is all the bones and shells. This is the archaeology of our capital's appetites. Lots of sheep bones from mutton, ox bones sawn in half for their marrow and oyster shells from when they were London's fast food and fit only for the poor to eat. Among this, because of the way the river deposits its light and heavy loads, you will find pottery and, best of all, clay pipes. These have very individual styles and can be easily dated with the right guide to hand. You might also find pieces of worked bone: a needle or a knife handle or maybe even bone dice or a child's toy.

Lower down the shore, you'll find the heavier pieces and the metal finds. Here your imagination is important. Pick up everything and guess its use. Ask yourself if the pattern is manmade: is that writing you see, a face, a bit of fleur-de-lis? Nothing from the past is as it seems; few objects reveal themselves at first glance, and early coins rarely look like today's loose change. Last month I found an Edward IV silver penny which looked like a grubby wafer of junk, as small as a fingernail, till I got it home and cleaned it up.

Even the most mundane-looking items can be treasure: that little twist of lead wiring in your hand might be part of a pilgrim's badge. These are my favourite. In the medieval period, when we cared a little more for our souls, our ancestors were drawn to wander to shrines across the land. "Thanne longen folk to goon on pilgrimages," as Chaucer wrote. Each shrine would have a badge, some plain, others intricate, which were simple proofs of devotions: their hopes for cure or thanksgiving or penitence. One of my best places to mudlark, by London Bridge, is a stone's throw from the site of The Tabard Inn in Southwark where The Canterbury Tales begins.

If I find something and don't know what it is, I go along to the Museum of London, which offers a free identification service. This is important. If it's really worth something and sheds light on our history, then the discovery must be shared. Amateurs like us have a huge part to play in piecing together our past. There's something else I have gained from these trips: a more intimate knowledge of the river. Over the years, I have seen the river in a thousand different moods: it never shows the same face twice. Down on an ancient shore, proper terra firma, unadorned by concrete or landscaping, you are dwarfed by the buildings that rise out of the embankments. And as you pick up the (literal) flotsam and jetsam of history, the tools our ancestors used to fashion this city, the bone and shell that fed them, you cannot help but be humbled by what they achieved.

Tips for the river bank

Always keep an eye on the tide and stay close to exit points

Walk on the shingle; avoid the mud itself

Report interesting finds. Contact Fay Simpson, Portable Antiquities Officer, at the Museum of London (0870-444 3852)

The Museum of London offers guided walks along the shore of the Thames, useful for your first foray

Don't dig unless you have a licence. You won't need to dig, but licences can be obtained from the Port of London Authority (020-7743 7900)

If you don't find anything interesting, cheat. Jane Stewart at Grays Antiques (020-7629 3868), has great mudlarked finds for sale