This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
Copper baths may also be finished with a planished surface, which looks bright and clean, but requires regular and frequent attention to keep it in proper condition.
Cast-iron baths can be finished with a porcelain enamel; and recent improvements in the preparation of the enamel warrant the hope, that this kind of finish will in future be of a more durable nature than it has hitherto been. The defect of all porcelain enamels on iron has been that the porcelain is brittle, and liable to be chipped off easily. If the iron be exposed, oxidation at once occurs, and the remainder of the surface is more or less spoilt. A method of applying the first coat has now been devised, which, it is claimed, gives a certain toughness to the enamel, by which ordinary chipping is almost if not quite prevented. The bath is first scrubbed with pumice stone and sand to a perfectly smooth surface. It is then heated to a red heat in an annealing furnace. This part of the process involves considerable risk to the bath, as, if unequal expansion takes place, the bath hursts. Though less than formerly, the proportion of failures from this cause is still about one in twelve. When the bath has passed success-fully through the first firing, it is again cleaned and coated with flint - glass, sand, and borax; this is called the "grip". It is then put into the kiln again, after which it receives the final coat of glass, china-clay, and whatever colouring matter is required. This done, it is again fired, and should emerge from the kiln with a perfectly smooth porcelain face. The advantages of a porcelain enamel are that it is unaffected by any kind of acid, or by any of the salts (such as Tidman's bay-salt) that are frequently used in baths. The painted enamel is, on the other hand, acted upon very quickly by inferior soaps, and by the salts referred to.
A special kind of copper bath, made by the Sanitary Bath Company, is formed with very thin and fine sheet-copper in three pieces, for head, foot, and body respectively. The sheets are tinned and planished, and the seams are then brazed, and covered and supported outside with cast-iron bands. Stamped steel baths arc made in a very similar way, the seams being of course soldered together. Both these kinds of bath are light and serviceable, and are moderate in price. The only objection to them is that, the metal being so very thin, the expansion caused by the admission of water, and also by a person getting in, is evidenced by somewhat startling noises.
Zinc baths are very little used in England. They are extensively used in France, and are also somewhat in favour in Scotland. The surface is usually polished, and when new looks clean and bright. To be kept up to this condition, however, it requires constant scrubbing, and great care to prevent contact for any length of time with greasy water. The amount of time and labour required to keep a polished zinc bath in proper condition, would bean impossibility in the average English household, and a zinc bath ill-kept soon becomes both unsightly and unclean. Fig. 256 shows different forms of zinc baths made by a French firm.
Fig. 256 Four Zinc Baths.
Slate baths are made of slabs of slate about one inch in thickness, held together with iron bolts. The slabs can of course be enamelled either black or white, or to imitate marble; hut the process is costly, and the result by no means satisfactory. There is, in fact, nothing to recommend the use of slate for this purpose, and very few baths are made of the material.
Fire-clay (or. as it is sometimes called, "porcelain") is now very largely used for baths. The material used is the well-known fire-clay from the Coal-measures. The clay is subjected to a process of weathering, grinding, tempering, and mixing with certain other ingredients, in which the greatest care is taken to obtain a substances, which will burn and contract with regularity throughout its entire thickness. It is tempered or brought to the required degree of plasticity by the addition of water, and is then thoroughly stirred and kneaded in a pug-mill. The baths are built up by hand over a wooden block of the shape required, and dressed by hand, and when dry are burned in specially -constructed ovens. When they emerge, the baths are in what is called the " biscuit " state; they are then enamelled inside with a porcelain glass, and are again Darned The process of burning in each stage occupies several days, and involves an appreciable percentage of risk from unequal expansion and contraction, and other causes. It will be seen, therefore, that the manufacture is necessarilv a costly one on account of the number of failures that inevitably occur. The introduction of fire-clay baths is due to a suggestion of the late Prince Consort. In 1846 the Society of Arts, of which his Royal Highness was President, offered a prize for the production of a glazed porcelain bath made in one piece. After a long and costly series of experiments, Messrs. Rufford of Stourbridge produced, in 1850, a porcelain bath which fulfilled all the conditions laid down by the Society, and for which the "Isis" gold medal was at once awarded. The manufacture thus started was destined to increase very largely as time went on. and to-day glazed porcelain baths are in large request, more especially for hospital-, asylums, and other public institutions.
Fire-clay baths have two great drawbacks, their great weight, and their feeble power of retaining heat. The first has within the last few years been largely reduced,1 but not without risk to the strength of the bath. The second is a physical property of the material, and cannot be altered. The great advantages of a porcelain bath are its durability, and the fact of being in one piece without seams or joints. The glaze is unaffected by acids or Baits, and can only be injured by wilful mischief The coldness of the material to the touch is, however unquestionably a real defect, and one which may be, in some cases - as when a hot bath is quickly needed - positively injurious. It is unfortunate, too. that it is practically impossible to enamel a fire-clay bath outside as well as inside If this could be done with reasonable safety, a fire-clay bath would be for all ordinary purposes perfect. The risk, however, of failure in the burning is too great, since it is impossible to ensure that no air is contained in the substances of the bath. If any air should be confined in the day, the coating of enamel on both sides quite prevents its escape, and the result is of necessity a failure.