Country diary: Down an old lead mine, an explosion of colour

At first I can’t believe that there’s a way in, the entrance is so hidden by downy willow, ferns and field rush. Just a trickle of rusty water hints at the opening to an abandoned mine. That we have to push through scrub to enter the underground world only adds to the excitement.

A long adit stretches before us, lit by our helmet torches, its arched stonework streaked and stained by minerals. We marvel at the precision and detail of the masonry, breathe in smells of damp earth and wood. Led by two miners from nearby Nenthead mines, we’re a small group of potters and artists working towards an exhibition inspired by lead mining in the North Pennines.

The colours are astonishing: vivid orange flows stained by iron; milky solidified waterfalls; raspberry-ripple pink from traces of cobalt; elephant-hide greys and sulphurous yellows. The roof gleams with stubby stalactites. Starting out as hollow tubes, they are known as soda straws, formed by central drops of water that deposit calcium carbonate around the tube’s rims. This mineral-saturated water encases and transforms – a tangle of what appears to be stone roots is in fact calcified bootlace fungus, the black rhizomorphs of honey fungus that once grew on the decaying timber of pit props or ladders but which are now entombed.

What entrances me most are the cave pearls, shiny ivory pebbles settled in a cupped nest. Drip by drip, they are made by calcium enclosing something as tiny as a grain of sand, the small vibration of each impact keeping them from adhering; this is the image that will stay with me.

Past flooded sumps, through the worked-out “flats” where lead was extracted, we reach a line of water spouts pouring through the side wall. They join the stream running down the adit that is our exit, the level breaching the top of my wellies; we emerge wet but elated.

At home, I make drawings of the cave pearls, my photos revealing new details: the shallow folds and channels converging on the bowl; the purity of colour, faintest honey on chalky white; pearls varying in size, some egg-shaped, some with delicately fluted edges. The act of drawing as a quiet recollection of a day underground.

• Under the Changing Skies: The Best of ********’s Country Diary, 2018-2024, is available now at guardianbookshop.com. Inspired 2026 is at Nenthead Mines from 8-9 August, 10am-4pm