The method employed of necessity depends upon several conditions - the nature of the clay obtainable, the character of the business and the conditions under which the goods must be produced. The one who has nothing but high-heat clay is forced to work at a high heat in order to produce solid goods, and the same is true throughout the scale. The manufacturer of glazed goods only should adopt the cheapest and best methods. The one who makes glazed goods simply as a side issue should adopt the method that is best suited to the conditions existing at his works. The reasons for this are obvious. Competition is close, and, while possibly to-day there may be sufficient profit in the business to stand expensive methods, the time is not far distant when only those who are fitted to manufacture fine goods at a low cost will be in existence.
There is no doubt that the single-fire process is cheaper than the double-fire process, and I believe there is very little doubt that as good material, and probably better, can be turned out by the single-fire process. The single-fire process requires more skill on the part of the practical man, and, as has been shown, requires a clay or clays suited to it. When these conditions are fulfilled I do not see how it is possible for the double-fire process to beat it in any way. I have heard the argument advanced that by the double-fire process the straight, perfect brick only need be enameled and the others sold without enameling, thereby avoiding the loss of the crooked brick or imperfect brick. The only answer to this argument is that by the single-fire process, with proper clay, properly handled, there should and will be extremely few crooked brick, and probably no more imperfect brick than will come out of the gloss kiln by the double-fire process. If this is the case, the difference in favor of single fire will be in the cost of the first burning by the double-fire process. I cannot see a single valid argument in favor of the quality of material produced by the double-fire method, and there are many against it, especially where the first burn is at a higher heat than the second.
There is also no doubt that in single-fire methods open placing is cheaper than placing in saggers. In regard to slip and glaze on one side and enamel on the other there is much argument Some claim finer effects for one and some for the other. One dipping is claimed for enamel as against two or three dippings for slip and glaze, and the smaller cost of material is claimed as an advantage for the slip and glaze process. We will consider the pros and cons. Slip will cost not over 50 cents per 1,000 brick and glaze from 50 cents to $2 per 1,000. Enamel will cost from $5 to $20 per 1,000, unless a lime enamel, and these are usually very uncertain. Dipping costs not over 75 cents per 1,000 for each dip, so that twice dipping only costs 75 cents more than a single dip, and three times dipping only $1.50 more than a single dip. The cost is evidently in favor of slip and glaze. I have always found glaze more reliable and certain than enamel. I cannot see any reason why there should be any advantage in enamel over glaze, except as cited, when heat used is too low to enable a slip to be well fastened, but do see why there should be an advantage in glaze over enamel. The glaze is relied upon simply for gloss and finish, and is not expected or supposed to help conceal the body. Slight variations in heat may vary the gloss slightly, but, with a proper slip under the glaze, does not change the color. Variations in thickness do not appreciably affect color. Enamel gives the gloss and at the same time has to hide the body. Enamel is not absolutely opaque, but is simply translucent, consequently variations in thickness or heat affect the color materially. As to glaze running and enamel not, it is all nonsense. Either can be made so that it will run or not, depending upon the way it is compounded. It is a little more difficult to keep an enamel from running, because it is necessary to put it on thicker than glaze. The greatest objection to enamel is the thickness with which it must be used. It will not flow out to a square edge, neither will a glaze, but the enamel, being used to a greater thickness, makes a rounded corner that is noticeable, and when brick are laid in the wall it is quite objectionable. The greatest objection to the slip and glaze process at a low heat is the great difficulty of attaching the slip to the brick. This Is not true at a high heat. At a high heat the clay itself in the slip burns solid and strong and becomes firmly fixed to the clay of the brick, but at a low heat this fixing must be done by using fluxes, and it becomes a problem of great nicety to avoid peeling on one side and translucency of slip on the other. Low-heat processes are evidently slightly cheaper than high-heat processes, but not so much so as one would think. After a kiln is once heated up to a low-heat finish it takes comparatively a small per cent more fuel to run it up to a high heat In other words, the bulk of the fuel is used in getting the kiln redhot. Low-heat clays usually feel variations in the fire more than high-heat clays, so do low-heat glazes and enamels, consequently low-heat processes are slightly more risky than high-heat processes.
Take it all through, then, considering cost of production and risk, the high-heat, single-fire, open-burning process, under good management, I have always felt, possesses an advantage of from $5 to $10 per 1,000 over any other process, all other things being equal. This is undoubtedly, then, the process for the maker of enameled goods only. But this does not imply that all other processes should be abandoned or that their users will be forced to abandon them. I do think that all other processes will be forced out of factories devoted only to glazed goods. But a great deal of glazed material can and will be made as a side issue, and where the process can be adapted to the machinery, processes and heat employed in the manufacture of the bulk of the business such glazed side issue can hardly fail to be profitable. Ofttimes the main business of the manufacturer gives him advantages on the glazed business through information obtained and facilities for production of the particular class of goods. Enameled brick can sometimes be made as a side issue at a very good profit, as they can be set in the kiln where the regular goods will not go, and consequently may be considered as occupying no room and taking an inappreciable amount of fueL The adaptation of the process to the heat and conditions existing is often difficult, but rarely impossible.