Madeley, Jan. 1st, 1877.
INTRODUCTION.
The Borough of Wenlock comprises places not only rich in historic interest but important also as centres of manufacturing industry; and none more so than those grouped within a mile or two of the Iron-bridge, itself a work of world-wide fame. “Broseley Pipes” and “Broseley Bricks,”—the latter including all similar productions emanating from Coalbrookdale, the Woodlands, Lady-Wood, Coleford, &c.—possess acknowledged merits which create for them a constant demand, whilst in higher branches of the art, where similar natural and other clays are used, Messrs. Maw, Craven, Dunnill, and Co., and Bathurst, find a still more extensive market for their goods.
From time immemorial the merits of these clays seem to have been known and recognised; if not from Early British, at any rate from the period when the armies of imperial Rome penetrated the Valley of the Severn, through intermediate ages, these beds of clay which give employment to thousands seem to have been used for some purpose or other, either for articles of ornament or of use. At Caersws, near Llandinam, on the left bank of the Severn, we have seen Roman bricks apparently with the initials of the workmen’s names upon them; whilst of pottery, cart loads have been found there and at Wroxeter, including a number of jars, bottles, urns, lamps, vases, &c., with hunting and other subjects. Some of the mortars, colanders, dishes, and similar kitchen utensils, are of coarse white clay, similar to that now used at Broseley. It is therefore evident from modern excavations that fifteen hundred years ago the value of these clays was known to the brick-makers and potters introduced by that enterprising people. Specimens of Norman and of later periods are rare, but certain evidences concur to make it clear that not only fifteen hundred years ago was the worth of these clays established, but that from that period to the present they have been used in one way or another.
The subject is therefore one of historical as well as of industrial interest, although those at present engaged in the various branches of manufacture may be too absorbed in turning the material to account to pause to note the stages the trades in which they are engaged have gone through.
It was the value of these clays which led to the establishment of works for the manufacture of porcelain at Caughley, Jackfield, Coalport, and Madeley, historical notices of which works will be found in the following pages, which are for the most part a reprint of articles that have appeared in the “Salopian and West-Midland Magazine.”
NATIVE CLAYS:
OR THOSE USED FOR
BRICKS & TILES, TESSELATED TILES,
POTTERY, &c.
Clay, as commonly understood, means earth of sufficient ductility to allow of its being kneaded by the hand into useful shapes or forms, and ranks as a raw material, or one not worked up or prepared for use. Some clays are soft, others are indurated, or hard and rocky: but all have, nevertheless, been in one sense prepared by poundings, washings, and mixings, carried on by Nature on a much larger scale than that on which they are now fitted for use. They differ in quality, in degree of firmness, and in colour, and show certain relationships by which it is clear that they are derived from sand, just as sand is derived from a hardy race of pebbles, which in turn bear a close relationship to rocks, from which undoubtedly they are also derived. Surface clays, used for making inferior bricks and tiles, whose earthy odour gives evidence of alumina, are often derived from red sandstone rocks, which have been ground down by machinery of waves or streams; whilst the deeper coal-measure clunches, used for firebricks and pottery, were originally the sediment thrown by rivers at their embouchures into inland lakes or seas. Common red clays, deriving their colour from iron, have many impurities, and contain a large percentage of alumina. Fire-clays are nearly free from iron, and contain a large amount of silica, whilst china-clay, or kaolin, contains felspar, sometimes with the impurities of soda and potash.
Let us first take brick and tile Clays. Of the three substances expressed by the three words of four letters—clay, coal, and gold, we question whether the first does not rank highest in importance. The latter may be the most coveted, but the former, we imagine, contributes most to the conveniences and comforts of mankind. It is in one form or another universally attainable. There is a great difference in its qualities; and when it is remembered that a porous brick made from bad clay will hold nearly a quart of water, the advantage of good clays producing good bricks which will protect health and property from the injurious effects of a fickle climate, becomes apparent. In addition to ordinary clays used for the manufacture of building materials, we have throughout the whole coalfields of Shropshire and Staffordshire superior fire-clays, which occur in a tough indurated state, and are known by the familiar name of clunches. They possess but a small portion of iron, which gives a red colour to ordinary clays, at the same time that they are distinguished by an almost entire absence of lime and alkalies; yet contain, on the other hand, that proportion of silica and alumina which although they cannot be melted by the strongest heat, form ingredients which during the process of burning combine to form an artificial stone capable of sustaining great heat. The following is an analysis of one of these fire-clays:—
| Silica | 61.91 |
| Alumina | 21.73 |
| Protoxide of Iron | 4.73 |
| Lime | 0.09 |
| Magnesia | 0.59 |
| Potash | 3.16 |
| Soda | 0.25 |
| Chloride of sodium | 0.08 |
| Organic matter | 0.70 |
| Water | 6.73 |
| 99.97 |