Slate

Geol­o­gists will tell you that slate is a meta­mor­phic rock com­posed of lay­ers of clay or vol­canic ash.  Most peo­ple are more famil­iar with it as a roof­ing mate­r­ial, or some­thing to write on, on the line between papyrus and vel­lum, and paper and IPads.

Slate is eas­ily recog­nis­able, a dark grey, smooth stone, found in Corn­wall, Wales, the Lake Dis­trict and Scot­land, as well as other parts of the world. In some places there are open quar­ries, such as at Delabole in North Corn­wall.  Welsh slate is often mined hun­dreds of metres under­ground, the deeper you get the older the slate.

Slate was formed mil­lions of years ago from shale or vol­canic ash, fused together under pres­sure.  It formed into very fine lay­ers, which are indi­vid­ual to every slate, much like the grain of wood. Slate is care­fully split along this grain to leave the flat sur­faces which are so recog­nis­able.  A good piece of slate with no defects will ring when tapped. Some slate has tiny flecks of iron pyrites in it (fool’s gold) or other min­er­als, which gives indi­vid­ual pieces a sparkly, coloured or rusty appear­ance, adding to the unique character.

Over the cen­turies, slate has been used for many things,  and worked its way into the Eng­lish lan­guage.  From at least Medieval times, slate has been used for roof­ing, and cladding build­ings.  Being smooth and light­weight, slate was also used as a writ­ing mate­r­ial.  Marks can be made and erased, and many chil­dren over the years learned to write on slates. And in bars, a slate was used to note bar charges, and tabs.  Hence the phrase ‘a clean slate’ or ‘blank slate’, when you’d paid your dues.

Where does HMIC’s slate come from?

Much of the new slate I use at HMIC is Cor­nish – often from Delabole, but also from Tre­vil­let Quarry, near Tin­tagel.  Slate from dif­fer­ent areas has slightly dif­fer­ent char­ac­ter­is­tics, and I some­times use Span­ish slate, which is finer, mak­ing it eas­ier to punch holes in.

I also use reclaimed slate, which has been taken from roofs across Corn­wall.  It’s not pos­si­ble to say which exact quarry they came from, as most farms used to have a quarry within a few miles. As time has gone by smaller quar­ries have closed and its now mainly Delabole Quarry that sup­plies Cor­nish slate in large quantities.

Reclaimed slate often has holes in it, or marks from the orig­i­nal use.  This makes each piece a unique, and there­fore all the items I make from reclaimed slate will be slightly dif­fer­ent from one another.  I’ll have to allow for chipped edges, or bro­ken cor­ners. Some­times I can use the orig­i­nal fix­ing holes, but this doesn’t always work out.

Using your slate products

If you are using some­thing made of slate with food, eg a lazy susan or serv­ing plate, then it will be cov­ered in a spe­cial coat­ing.  This will pro­tect the food from any­thing in the slate, but it won’t entirely pro­tect the slate from any grease in the food.  I would rec­om­mend lightly coat­ing your slate with cook­ing oil, roughly once a year, to pre­vent it from absorb­ing grease, which would stain it.

If you have pur­chased a gar­den orna­ment or water fea­ture, you can be sure that it is frost-proof.  Slate absorbs very lit­tle water, which is why it has been used for roof­ing for so many years.  How­ever, if you have a water-feature, I would rec­om­mend emp­ty­ing it if the tem­per­a­ture is likely to drop below freez­ing, so that the seams aren’t popped as the water in the reser­voir solidifies.