Darning a wool sock heel on a mushroom, one row at a time

row 1 of 4

Finding where the hole actually ends

A hole in a sock is only the small visible part of a much larger thin patch. By the time daylight shows through, the stitches around it have been felting and wearing for weeks, and if I darn only the hole I am sewing new yarn onto fabric that will give way within a month. The first thing I do is turn the sock inside out, pull it over the darning mushroom and hold it up to the window in the back room. The thin area shows as a paler, slightly see-through region, often shaped like a lemon lying on its side, and it is nearly always twice the size of the hole.

I mark the edge of that region with a few tacking stitches in a contrasting cotton, going round about a centimetre outside the point where the knitting still looks sound. Those stitches come out at the end. Before I learned to do this I judged the edge by feel, pressing the fabric with a thumb, and I was consistently too generous to the old knitting. On a sock that has been worn through a whole winter, the stitches beside a hole are rarely as sound as they look, because the fibres have thinned inside each loop even where the loop itself is intact.

The shape matters as well. A darn works best as a rectangle or a rounded square, laid with its sides running along the columns and rows of the knitting. A darn that follows the ragged outline of the hole puckers when the sock is stretched over a heel, since the new weave pulls differently at every edge. I tack out a rectangle and accept that it covers some knitting that did not strictly need covering.

row 2 of 4

The yarn, the needle and the mushroom

For wool socks I darn in wool, and I try to match the weight of the yarn rather than its colour. A darn in yarn heavier than the sock makes a hard ridge under the heel that you feel with every step by the end of a walk to the station. A darn in thinner yarn wears through again before the rest of the sock has noticed. Most hand-knitted socks that come my way are in a four-ply sock yarn with a little nylon in it, and I keep a drawer of leftover balls in that weight, mostly given to me by people at the mending table who finished a project and could not bring themselves to throw the ends away.

Colour is a matter of taste. I usually pick something that contrasts, because a darn is going to be visible whatever I do and I would rather it looked intended. A charcoal sock with a rust-coloured heel has more going for it than one where I spent an hour trying to match a grey and still got it two shades out.

row 3 of 4

Laying the warp and weaving across it

The warp goes in first, running the same way as the columns of knitting. I start at one corner of the tacked rectangle, a few stitches inside sound fabric, and take small running stitches up the column, then across the hole in one long float, then into the sound fabric on the far side and a few stitches past the tacking. At the end of each pass I turn and come back down the next column, leaving a small loop at the turn instead of pulling the yarn snug. Those loops are the allowance for the sock stretching over a heel and for the wool shrinking a little in the wash.

The warp threads should lie side by side, touching, with no gaps between them over the hole. On a four-ply sock that means one warp thread for each column of knitting, sometimes a little closer. With the warp complete the darn looks like a patch of parallel strings stretched across a gap, and it is tempting at that stage to feel the hard part is over. It is not. The warp has no strength sideways at all until it has been woven.

The weft goes across at right angles, over one warp thread and under the next, then back again under the ones it went over. I use the tip of the needle to push each row down against the one before, the way a weaver uses a beater, until the rows sit close enough that no light shows when I hold the mushroom up. Weaving is where the time goes. A heel darn about four centimetres by five takes me a little over an hour, longer if the radio has something good on.

row 4 of 4

Tension, and the darn I had to unpick

The mistake I made most often in those first winters was pulling tight. It feels right at the time, because a tight darn looks neat and flat on the mushroom. Off the mushroom and on a foot, a tight darn does not stretch with the knitting around it, so its edges take all the strain and the old fabric tears along the boundary. A pair of my own socks went that way within three weeks, leaving a perfectly good woven patch sitting in the middle of a new hole shaped like a picture frame.

These days I check the tension three times while I work: after the warp, halfway through the weft and at the end, each time by pulling the sock off the mushroom and stretching the heel gently over my hand. If the darn ripples or the fabric around it gathers, I ease the loops at the turns before going on. It is slower, and unpicking half an hour of weaving because I forgot to check is slower still.

When the darn is done I pull out the tacking, run the tails back through the darn for a few centimetres in each direction, and put the sock through a cool wash. The first wash is when the darn stops looking like a patch and starts looking like part of the sock. There are socks in my drawer on their third heel darn and one pair on its fifth, which is probably past the point of sense, though the rest of each sock is still going.