The versatility of clay

 One of the first things I touch every morning, without fail, is clay - my essential early morning coffee comes in a plain glazed mug. I am also completely surrounded by clay, whether at home or at work, by the brickwork that fills in the walling, whether exposed as face-brick, or hiding behind a coat of plaster.

Yellow face-brick common throughout Johannesburg

I often forget how fundamental clay is to our evolution as humans, with different manufacturing techniques, distinctive shapes, and pattern designs, whether etched or painted, being used by archaeologists to reconstruct timelines and evidence of habitation. The making of pottery is one of the oldest pursuits of us as humans, whether using sophisticated industrial processes to achieve consistency...

Arzberg china, typically the architect's choice of crockery

or whether hand-made, as an artistic expression...

Handmade bowl by Bronwen Lankers-Byrne

Clay is a wonderfully versatile material, and very easy to work with, as most of us have found since an early age - I remember making mud pies with my sister for dolls' tea parties, decorated with flowers and berries, and forming miniature farm animals from the sticky red soil unearthed when plumbers came to dig up the pipes. I have a small collection of artefacts, replicas from different eras and countries, that range from an oval shepherd's flute from Greece, to an oil lamp from Roman Britain. 

A Roman house plaque (back), shepherd's flute (left), neoclassical decoration (right) and Roman oil lamp (front)

All of these are made from terracotta, an iron-rich clay that is quite porous, so ideal as a wine cooler, but less useful for any receptacle for liquids. The invention of glazing opened up clay to a very wide variety of uses, prized for its hygienic uses (the porcelain toilet bowl) as well as its impermeability. It also opens up a wide range of possibilities for surface treatment, as the glaze can be made in many colours for painting or printing designs.

A collection of glazed containers

But my enduring fascination for clay is as a building material, in the form of brickwork, as well as for roof tiles and detailed elements such as window sills. The colour of the brickwork will tend to be quite distinctive for any region, a direct link to the geological formations where the clay is sourced. In some parts, this can be quite diverse: when I lived in Melville, we were half-way up a slope, with deep red soil, but friends at the top of the road had a very pale grey clay - the same geology, but at the higher points, the iron had leached out of the soil, removing the reddish colour. In the south of Johannesburg, where the largest industrial brick-making industries are found, the clay is a yellow-ochre colour, with a bit of variation into the mid-brown range (as in my first photo).

In parts of the world where there is a complex geology, one often finds an architectural style evolving that flourishes with the variety of brick colours, used to accentuate different parts of the buildings. Originally, the choice of colour for different elements of the building would relate to the hardness of the brick - this would vary depending on the chemical composition and the amount (length and temperature) of firing. The harder brick would be used for the outer corners (replacing the traditional stone 'quoining' as a cheaper solution) and for the window and door surrounds.

Victorian brickwork often appears in several colours on one building

The other aesthetic that one often finds in historical buildings of face-brick is one that comes from being able to shape the bricks, either before firing, or by chipping or rubbing the finished component. Rubbing is common where the bricks are given a wedge shape to form an arch: this is also structural, as the bricks will tend to be much more resilient to cracking than the mortar in between. The compressive forces from the weight of the walling above the arch will be carried down to the sides of the arch so a wedge-shaped brick, or voissoir, will minimise the amount of weaker mortar.

A brick arch at Amersham in the UK

The photo of the arch also shows another distinctive feature of historic brickwork, in the shaping of the bricks to mimic stone columns or pilasters. This would be achieved by a combination of chipping and rubbing to get a smooth surface, a very labour-intensive process. For buildings using many of the same specialised shape, a mould would be created, and either the soft clay would be forced into it and then taken out of the mould to harden before firing, or a very runny mixture of clay and water (called 'slip') would be poured into a sand mould. The excess water is absorbed by the sand until the element can hold its shape, at which point the sand is removed. This is the technique used to make porcelain toilets, which is how its complex shapes can be created.

One can just make out the moulded detail above the first floor windows (Chelsea, London)

These days, brickwork is quite rare, as this material has been largely replaced with concrete bricks and blocks as a cheaper and more consistent alternative, especially if the wall is to be plastered and painted. When one does find face-brick (generally chosen for its very low maintenance demands), it tends to be used merely as a facing to a concrete or steel structure, or for infill panels, so the full repertoire of this potentially beautiful material is lost, along with the craftsmanship needed to achieve this aesthetic.