The chief kinds of bricks at present in the market, and their characteristics, are as follows : -
Gaults are bricks made from a natural clay with sufficient lime in the form of chalk to act as a flux. They are made in the southern and eastern counties, and are very hard, heavy, and durable, of the first quality, suit-able for best facings, and usually of a white colour, though the inferior bricks have a slight pinky tinge. The Cambridge common white bricks have a proportion of pinky ones, the mixture being classified as Mingles.
Malms, as the name implies, are made from a marl or chalky mixture, and principally used for facings and other best work. Suffolk bricks are of a similar quality, and mostly of a light colour.
Common firebricks are made from a refractory clay containing almost pure alumina and silica in the proportion of one part of the former to three parts of the latter; they are generally of a whitish yellow or light brown colour, and rather porous. They should be uniform in texture, and of course free from lime and iron. They are made chiefly in Shropshire, Staffordshire, and near Leeds, Newcastle, and Stourbridge. They are used for lining blast furnaces, setting grates and boilers, and casing fire-resisting flues and furnaces, and in fact in any position where brickwork is exposed to the action of fire.
Dinas firebricks are made in Glamorganshire from sand, i.e., pure silica, which is mixed with 1 per cent, of lime and a little water, and pressed together by machinery before burning. They are the best firebricks in existence, of a porous nature, and they will expand and withstand an enormous heat.
Ganister bricks are made from a hard fireclay marl found in the coal measures, which is ground and pugged and moulded in the ordinary way. They are closer in grain, and superior to firebricks for furnaces, etc.
Guistnuyda firebricks are similar to the Dinas bricks.
Lee Moor firebricks are made near Plymouth, from the refuse of china and clay, and are very hard, compact, and of a dull red colour.
Thompson's are light, strong, fireproof bricks, lately introduced from Cheshire; they are of a common red colour, and extraordinarily light in weight.
Glazed bricks are made extensively in the south-west of Scotland, in Wales, Warwickshire, Yorkshire, Northumberland, and Durham, from the best qualities of fire-clay, which is generally ground much finer than for firebricks. Glazed bricks are made by hand and machinery (the latter chiefly), and all, when sufficiently dry, are pressed and as fine a skin put on them as possible; after which the glaze, of whatever tint required, is put on by either of two methods, called respectively the dry and wet dip. Of these two methods the former is the better, because the previous drying (as hereinafter explained) prevents any further contraction.
The dry dip consists of dipping the bricks in the glaze after they have been once burnt in the kiln; whereas, in the "wet dip" process, the glaze is applied to the wet, undried, or unburnt bricks. After they have been dipped each process is completed by burning the bricks at a very high temperature. Glazed bricks are generally one-eighth of an inch higher than the ordinary kinds, so as to reduce the mortar joint; and they may be either glazed at one end or one side only, or at both ends, both sides, or on end and side as required.
Fareham and Woodville red bricks are of a close, sandy nature; or they can be made smooth, coming from a moderately plastic clay. Their deep red, even colour, and good surface, render them most suitable for facings.
Staffordshire or Nuneaton blue and black bricks are very hard, well-burnt and close, non-absorbent, and will resist enormous weights and pressure. They are used for damp courses, pavings, weatherings, piers, dressings, and positions requiring great compressive strength, and for damp situations. They are made from a clay containing about 10 per cent, of oxide of iron, which gives them their colour. The clay is also made into copings, channels, and many other specialities.
Black bricks, made in Berkshire, have no uniformity in colour, but are hard, close, and sandy in texture, and make a good mottled front, their ends being alternately black, blue, and a glazed yellow or white: so much so that they give the appearance of being daubed irregularly with soot before being burnt.
Rubber bricks are of a soft, sandy nature, of fine, rich, red colour, and capable of being cut, carved, or rubbed into any shape or form. They are made near Birmingham and Bracknell, and should be compact, of uniform colour, texture, and hardness, so that they cannot be scored with a knife, even in the centre; while they should rub well. They are generally made slightly larger than ordinary bricks, to allow for the rubbing down.
Dutch or adamantine clinkers are small, cream-coloured, and very hard bricks, vitrified throughout, and used chiefly for paving; and, if anything, the Adamantine is the better brick of the two for the purposes required. They are grooved or chamfered, to give a firmer foothold for horses, etc., in pavings.