This article appeared in the Summer 1966 (Issue #4) edition of the Kent Archaeological Review.
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Excavation of a 19th Century Clamp.
Members of the Herne Bay Record Society group recently examined a reported patch of burnt clay at Shelvingford Farm, Hoath, near Herne Bay. The farmer had found ploughing difficult after clearing an old orchard in the spring, but a detailed examination was then impossible due to sowing.
After harvest, the site was again visited, and trial holes were dug. The NG reference is TR 2095 6552, in a large field sloping gradually to the stream from Ford to the Wantsum marshes. A blackened area of silty clay about 8 inches below the surface extended about 40 feet by 35 feet; the central part of this had been subjected to very great heat, and was burnt brick-red in colour, with a corresponding brick texture. This central patch was about 30 feet in diameter, and was at least 7 inches thick in places. Even where the red clay was thickest, it was underlaid by blackened clay, the colour of which lightened gradually to the natural brown beneath.
The longer axis of the black patch was North-South, and the northern end of both black and red areas was eroded from a point where the slope increased in the direction of the stream.
The only finds were pieces of brick (wasters?) covered on all faces with a salty glaze, from the topsoil all over the site, and this suggests the identification of the site. Encyc. Brit. volume 4 page 114, under "BRICK" describes Clamp Burning as a method of burning bricks in what are called clamps -- devised perhaps towards the beginning of the 19th century. The bricks are piled up to form a heap which may contain as many as a million, and wood fuel is incorporated in the heap. The fire is started at the bottom, and finally the whole thing burns for up to six weeks. The results are uncertain, with a considerable proportion of waste by over and under burning. N Davey, in History of Building Materials, page 65, states that the red colour of bricks is produced at a temperature of 900-1000 degrees C in an oxidising atmosphere.
If this is in fact a 19th century clamp, a date for the site may be suggested by a brick in an outbuilding at the Farm which was dated 1866 before firing.
Mr Frank Jenkins has investigated a similar site in a stream valley parallel with this one three miles away at Calcott, Surrey.