In her new book, Natural Glazes: Collecting and Making, Scottish potter Miranda Forrest sings the praises of the common horsetail. Not horsehairs, which are popular with potters who burnish and pit fire porcelain pots thus creating delicately beautiful surface lines, but horsetails, Equisetaceae, the flowerless plant found throughout most of the world these last one hundred million years.
High in silica content, Equisetacae have been used as scrub brushes in several cultures including that of colonial America. They are poisonous to livestock and, in many regions, considered invasive. They grow in the heavy clay beneath my pink Meidiland roses and, though a weed that I battle every summer, I do think they are pretty. I like the jointed, bamboo-like stems and the scratchy green bristles. Now there is a reason to love them.
Forrest writes, “The first test with horsetail ash alone produced a melted, creamy, greenish glaze with an optical blue in the centre, perhaps the most interesting single land-vegetation result to date. It also mixes well with other ashes and rock dusts. One of the other interesting effects associated with horsetail is carbon trapping during the firing, which gives a dark smoky colour to the glaze in places.”
Forrest, who lives in the windswept Outer Hebrides along the west coast of Scotland, has spent years collecting and testing local materials for glazes. She gathers land vegetation such as stinging nettles, Japanese knotweed, lawn grass, meadow flowers, and cereal straw, plus, from the beaches, sea vegetation like kelp. She carefully burns her gatherings to make ash, taking care not to contaminate them. She also gathers and tests stone dust such as gneiss and feldspar, and animal ingredients such as shells and bones.
Forrest keeps meticulous records of her tests, trying each found ingredient singly, and then in mixtures, sometimes using commercial additions like Cornish Stone. Though her work is intensely local, Forrest’s methods can be used anywhere with one’s own indigenous materials. She does, of course, discuss the more often written about wood ash glazes, but happily for us, she does not live in a wooded area, so of necessity she had to turn to other vegetation, thus opening many exciting possibilities for all of us.
This spring, I not only look forward to the emergence of the daffodils in our fields, but, and this is a first, to the return of the stinging nettles and horsetails! Fortunately, Japanese Knotweed has not invaded my gardens yet, but I know where there’s a patch nearby.