I have known Karl J Williams for a number of years and the first I knew of his sculpting skill was when he brought to me a carved stone and, knowing I was a Cornish geologist, asked me what kind of stone it was. To begin with Karl’s sculpting was mainly in Pentewan Stone, mainly in the form of rounded boulders picked up from the beach near where he used to live at Hallane. The natural form of the boulder was used by Karl to great effect to produce a sculpture which fitted the shape. Right from the beginning it was clear that a considerable talent was at work. Later on, Karl started to carve the much harder and more difficult to sculpt Black Head greenstone.

Pentewan Stone [1] is a type of elvan and is probably the finest freestone available in Cornwall. It occurs in narrow bands in the cliffs at Polrudden Cove, north of Pentewan, where it was worked since Medieval times and it also was worked in a large quarry north of Pentewan village. Both quarries are now long closed and the main source of stone nowadays is beach boulders along the coast between Pentewan and Black Head. Many listed buildings were built of Pentewan Stone, such as Holy Trinity Church, St Austell, Place House in Fowey and Antony House, Torpoint. It is resistant to weathering, as the 500 year old carvings on St Austell Church tower testify. What a pity the architect of Truro Cathedral did not select Pentewan Stone instead of the inferior Bath Stone which was used, and is now causing so much trouble and expense! Pentewan Stone is a true freestone, which means it can be readily carved into intricate shapes. Karl’s masterly sculpture of Askelepios [2] demonstrates how fine detail can be represented. Geologically Pentewan Stone is a felsitic elvan dyke and has a similar composition to granite but, as it cooled much more rapidly than granite, it did not allow enough time for large crystals form, so is much finer grained. This makes it more suitable for sculpting. Many of the elvans in and around the St Austell granite have been affected by the process of china clay formation, known as kaolinization, making them inferior to Pentewan Stone, which has not been affected by this process. However, it has been affected by a process known as greisening, which happily makes it more resistant to weathering [3].

The Black Head dolerite is a kind of rock which colloquially is known as greenstone, often called ‘blue elvan’ by quarrymen It is similar to the famous Cataclews Stone found in Churches around the Camel Estuary. Cataclews is a difficult stone to carve, but one particular medieval sculptor active in that area seems to have mastered the art of carving Cataclews Stone; we do not know his name, but architectural historians call him ‘The Master of St Endellion’. Karl is truly the ‘Master of Black Head blue elvan’! The stone is a dark bluish-green and is, in geological terms, a quartz-dolerite. It is many millions of years older than Cataclews Stone and possibly represents magma which cooled in a magma chamber beneath an ancient undersea volcano. Some of the stones used by Karl have been slightly weathered to produce an attractive mottled effect. I have a wonderful Green Man carved by Karl from slightly weathered dolerite, who guards the premises!

I am delighted to hear that Karl’s work is now getting the international recognition which it so richly deserves.

Colin Bristow, December 2018


[1] For further detail on Pentewan Stone and Cornish greenstones, see: Bristow, C.M. The geology of the building and decorative stones of Cornwall, UK. In: Special Publication 391, published by the Geological Society in 2014, pp 93-120.

[2] Asklepios is the Greek God of medicine. This bust is now in the reception area of the Peninsula Medical School, Truro. A photograph of the bust is in the reference quoted above.

[3] For further detail on the weathering of Pentewan Stone see; Mottershead, D.N. 2000 Weathering of coastal defensive structures in south-west England: a 500 year stone durability trial. Earth Surface Processes and Landforms, 25, 1143-1159.

Colin Bristow

Prominent economic geologist, author and lecturer. Distinguished contributions to the knowledge and development of industrial mineral resources worldwide, particularly kaolin and ball clay.

Colin M. Bristow was educated at the University of Bristol, England, where he studied geology. In 1958 he was involved in founding the first Geological Society in Kenya. He received an M.Sc. from the University of Exeter. While at Exeter he developed a technique using single probe resistivity to locate air filled cavities. This is now known worldwide as the Bristow Method.

Mr. Bristow joined English China Clays as a geologist and served the company until his retirement in 1991. He has been visiting professor of Industrial Geology at the Camborne School of Mines since 1988 and still retains the position of consultant with ECG. He has written numerous papers concerning the genesis and classification of kaolin deposits and the economic aspects of world kaolins.