Hand-moulded bricks

Derby Silk Mill 008

Machine pressed common bricks are the natural targets for brick collectors. Many of these are impressed with the producers’ names or trade-marks and so it is reasonably easy, with a little trouble, to identify their manufacturers and approximate age. The exact date of the first brick-making machine is the subject of some debate but bricks of this type start to appear after about 1855. In the last decades of the nineteenth century mechanical presses came to dominate production. Recently I have become interested in an older industry in which bricks were hand-made using a wooden mould using techniques not much changed from the Middle Ages. The first Bradford historical records of which I am aware date from the early eighteenth century. In 1718 John Stanhope of Eccleshill wanted to build a new hall. He reached an agreement with John Brown of Nottingham who promised to ‘dig and throw sufficient clay to make 100,000 good stock bricks’. The bricks were large by modern standards, being 10 inches long, 5 inches broad, and 2.5 inches thick, when burned.

It goes without saying that the term 'hand-moulded brick' would have had no meaning whatever prior to 1855 since up to then it was the sole method of production. Contemporary historical records, if any, will simply describe them as bricks. Field names with brick related elements, or buildings known as Red Hall, are common indicators of early brick production and use within West Yorkshire. Map evidence strongly suggests that, locally, brick-fields or brick kiln closes preceded established brick works. There probably were no permanent premises on such sites; brick-fields were leased by their owners, for short periods, to itinerant brick-makers who would have dug clay and fired hand-moulded plain bricks either in clamps, or alternatively temporary Scotch kilns. Some of these brick-fields survived long enough to be mapped in the mid-nineteenth century but they were eventually replaced by more permanent works whose owners, in this area at least, had the capital to buy machinery to grind up and fire local mudstones (shales) to produce their bricks.

Mechanical crushed mudstones from the Millstone Grit or Coal Measures were not used for hand-moulding. The hand-moulders dug beds of alluvial clay for their raw material. Alluvium is Quaternary period material deposited from water in a non-marine environment but unconsolidated into a rock. It contains particles of grit and sand as well as clay. Clays consist of fine particles originally laid down in low energy depositional environments. I assume that in the Bradford area alluvial deposits formed in glacial lakes, not from glacier-carried deposits or boulder clay. Chemically they consist of various aluminium silicates although given the stability of quartz this is also likely to be present. Most UK subsoil clays will make an acceptable brick but some were of better quality or were more easily exploited commercially. I am confident that there were Bradford brick fields in the following locations: Eccleshill, Manningham, Frizinghall, Shipley, Wilsden, Bowling, Low Moor, Leeds Road and Undercliffe.  Probably there were more.

Generally bricks, like pottery, were made from a mixture of clay, sand, and a non-plastic additive called temper or grog. These elements were combined with water to create a plastic mixture of the correct consistency. Some clays needed to be exposed to winter freezing before use and occasionally a good clay was used to sweeten a less effective material. It is exactly these details, of how brick-makers made the best of the raw materials available to them, that we completely lack for our local industry. Silica sand, when added to pure clay as a temper, prevents the cracking, shrinking and warping which would occur with clay alone as it dried. An excess of sand, however, rendered the bricks too brittle and destroyed internal cohesion. It is said that 25% sand was the optimum percentage. The most common form of clay used for everyday bricks, was that with a sandy consistency. Some brick clays contained organic matter which speeds up the subsequent burning when the bricks were fired. Clays in this area usually contain small quantities of iron oxide.

The process of brick-making involved putting the clay, water and additives into a large pit (later an iron container) where it was all mixed together by a tempering wheel powered by a horse, or later a steam engine. Once the mixture is of the correct consistency, and plastic, it is removed and pressed into moulds by hand. Each maker would have had his own personal moulds which were basically wooden but lined with brass or iron. To prevent the brick from sticking the mould was coated either with water or sand. The process was named slop moulding when the mould is dipped in water and sand struck when coated in sand. Coating the brick with sand gives a better overall finish to the brick but it would appear that slop moulding was commoner in northern Britain. In the slop moulding process a warp or clot of the clay mixture would be thrown into the wetted mould and pressed down with a wooden plane. The excess clay was scraped off the surface of the mould with a wire bow and further smoothing achieved with a wooden strike. The completed brick was turned out onto a wooden pallet for preliminary drying on a nearby flat. When dry enough to handle the maker’s lad would convey the ‘green’ bricks in a hack-barrow to the main drying floor or hack. Brick moulds and a hack-barrow at the Silk Mill Museum, Derby are illustrated.

In the hack the bricks were laid outside to dry by air and sun for some days. Once adequately dried the bricks were fired or burnt in a kiln or clamp. During this process first the water is driven off, next any organic material burns, and finally at a higher temperature (but well below the melting point of the fabric) the aluminium silicate and silica minerals sinter, or start to fuse. This will be around 1000+/-100ºC. The iron oxide in the clay acts as a flux enabling the silica and alumina to fuse which adds considerably to the hardness and strength of the final brick. The chemical processes are quite complicated but it is not usually necessary to enquire exactly what reactions occur and at what temperature. The term aluminosilicate minerals covers the fabric of bricks nicely. At higher temperatures still further melting occurs with, effectively, glasses being produced. Such a brick is more brittle but is almost impervious to water. One of the skills of the brick-burner was knowing how to achieve these results. Once the bricks were removed from the kiln time was allowed for them to mature. Newly fired bricks incorporate water into their fabrics quite quickly and increase in volume as a result.

The iron content of the brick was also responsible for its colour. A clay which burns to a red colour will provide a stronger brick than a clay which burns to a white or yellow brick. Any lime content in a brick has two effects. It stops the raw brick from shrinking and drying out, and it also acts as a flux during burning which causes the silica to melt and creates the bond which binds all the components of the brick together. Nodules of lime can be burned to quicklime during firing and any amount of quicklime (calcium oxide) within a brick fabric is detrimental to its quality and can cause the brick to split into pieces. For this reason it was inadvisable to use crushed lime as a temper.

Can anything be learned from examination of the bricks themselves? There is no evidence that ground-up shale was ever used as the sole raw material for hand-moulded bricks; to do so would have been technically very difficult. The opposite situation, that alluvial clay mixture was sometimes used in a brick-making press cannot be ruled out. Indeed if what I have recorded elsewhere concerning brick production by the Button family at Soil Hill, Halifax is true then this must be the technique they adopted, using a hand press. I know of no evidence that any type of brick-making press, however powered, was in use before 1850. Unfortunately there is no date available after which one can say that a local brick must be machine pressed. I have newspaper evidence that hand made bricks were being made as ordinary commercial items in Bolton Woods in 1875 when brick-presses had been available for a generation. It is quite possible that a single manufacturer could have produced all types of brick: alluvial clay bricks; machine-pressed (probably in a hand operated press) and shale bricks; machine-pressed.

Alluvial clay can be identified with some certainty in brick fragments. The signs of mixing of clays with different iron content (and consequently of different colours) will usually be visible. Inclusions present in the clay, or added as temper, such as small stones or pieces of fired shale will be readily detected. The fabric of machine-pressed brick is a much more uniform and monotonous product, as would be predicted from its method of production. Clay clots may not have filled the hand moulds completely with a result that fine creases in the fabric may be visible on the brick stretchers. You would expect the arrises at the bottom of the brick would not be completely sharp, but this would be hard to assess in a worn brick. Having read all this you will naturally wish to rush out to start making your own collections. Good hunting!

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