Slate is basically clay or volcanic ash that had previously formed on ocean floors and was subject to unimaginable heat and overwhelming pressure approximately 360 to 544 million years ago when the earth was still incredibly volcanic. This process caused the molecular structure to realign and form a fine-grained homogenous metamorphic rock (slate) that is characterized by its ability to split into thin sheets. Slate is chemically resistant, waterproof and non-combustible, making it an excellent roofing tile or artistic medium for slate sculptures.
Slate was an incredibly important resource during the Industrial Revolution, and in the 1870’s Welsh Slate accounted for 80% of all slate used in the UK. It is mined out of veins of shale using specialist equipment. It is an incredibly wasteful process however, as for every ton of slate produced, 9 tons of waste slate is also produced.
Stephen Kettle has trialled several different types of slate from different areas for use in his slate sculptures, and has settled on using Welsh Slate. His standard choice of slate originates from Caernaefonshire, which has purple and green colourings and is produced in open quarries. For select projects, he sometimes uses fine quality slate from the Llechwedd quarry in Blaenau Ffestiniog, a blue grey slate that splits extremely well and has very few impurities. In order to make his contribution to recycling, Stephen only uses waste slate. This is comprised of oddly shaped or broken slats of slate, which are ideal for his varied creations.
Welsh rocks, of which slate is the foremost, are incredibly important historically as there are few places on the planet with such a rich geological heritage. Many classic works were written about Welsh rocks and Welsh place names such as Llandovery and Llandvirn are commonplace in many well respected geological papers. Charles Darwin accompanied Adam Sedgwick, Professor of Geology at Cambridge, on a tour of North Wales in 1832. This journey arguably contributed to his analysis of the fossil record, which relied significantly upon fossils found in Wales. As a sculptural medium, slate sculptures cannot be matched by any other substance on earth in terms of beauty. It is smooth when dry and glistens when wet. It is incredibly durable and incises cleanly, meaning even slate buildings, gravestones and slate sculptures built hundreds of years ago look as good as new today.