The use of glazed clay products in buildings is of very ancient origin. Specimens of this character of work are in existence to-day which are supposed to be between three and four thousand years old, and the surface is as perfect as the day it was made. These ancient clayworkere evidently understood their business thoroughly. There may have been bad work, also; if so, it has not lived to tell the tale, and so it will be - good material will outlast generations, while the poor stuff will hardly outlast its maker. In building, the most essential property of the material used should be durability; after that we can look for beauty of form, of finish and of color, and artistic blendings of these into a pleasing and useful whole, but without durability we are building simply for to-day, and, besides this, what is more displeasing than signs of premature decay.
Glazed clay has been used in buildings in the United States for a few years. During that time its use has decidedly increased, but still it may be said to have barely commenced. The demand for such material is evidently not a fad, but has been almost forced upon the architects by the many merits of the perfect article, beauty and cleanliness being among these, but the latter is undoubtedly one of the principal merits. The perfect glazed surface will be washed clean by every heavy rain, and will not absorb any of the moisture.
The introduction of glazed clay products has been considerably constrained by the fact that all goods of this class are not perfect, and consequently there has been a lack of confidence on the part of architects as to their standing qualities, when used for external work in our severe climate. This lack of confidence is being gradually removed, due to the improvement made by our manufacturers, and, with its removal, we find a demand springing up, and growing at a tremendous pace, for the higher class and more artistic material in terra cotta, both for inside and outside work, but this demand can only be sustained by the production of perfect goods.
The two greatest causes that interfere with the production of perfect material of this class are peeling or shelling and crazing. The first of these is a fatal defect, but, fortunately, one that is not very prevalent, while the second is, unfortunately, almost universally prevalent to a greater or less extent. The question as to what extent crazing militates against the usefulness of the material is a very pertinent one, but still more pertinent is the question, How can it be avoided?
In light colored surfaces crazing is certainly unsightly, and the crazed places collect dirt; consequently the material does not possess the merit of cleanliness to its fullest extent In dark colored surfaces an extremely careful examination may be necessary to detect the crazing, and consequently the appearance of the surface is not affected, but the element of un-cleanliness still remains. Under the head of how to avoid crazing, I think the fact will be brought out that it does not increase peeling, but, on the contrary, it will be shown that glazed surfaces which craze are less apt to peel than those which do not craze. I do not mean to imply that the absence of crazing would indicate peeling; not at all. The perfect material will neither craze nor peel, and the imperfect material, unless horribly bad, is not apt to develop both difficulties. If horribly bad, both difficulties will possibly show themselves so quickly that the material will never be laid in the wall. Whether crazing leads to disintegration and decay or not, it certainly does lead to the appearance of it, and, so far as this goes, must be considered as a grave defect. The fact that makers of glazed goods try so hard to avoid crazing proves conclusively, without further argument on my part, that it is considered a grave defect
The subject of crazing seems to be surrounded by more of mystery and seems more difficult to overcome than any other one trouble met with by the manufacturer of glazed material. I have never yet talked with any one having a knowledge of the subject who had any idea of the existence or possibility of the existence of any law governing it, but all seem to think it is a matter largely of chance, and only to be overcome by constant experimenting, and experimenting guided by no fixed idea or principle, but simply conducted haphazard. If results be favorable, well and good; if not try, try again, either until favorable results are obtained or until the problem has to be abandoned, due to the exhaustion either of the experimenter's patience or pocketbook. Glazers are usually very secretive, and it may have been, in the conversations I have held with them on this subject my impressions were derived more from a determination on their part not to advance their ideas than from a lack of them.
There undoubtedly is a law governing crazing, as there is governing all phenomena. The great difficulty is to ascertain this law. All laws have been established through theories. At first the theory advanced may have been only partially correct, or later developments may have entirely exploded it, but without a theory advanced, to be either exploded or sustained, a law can hardly be discovered.
I have held a theory or principle in regard to crazing for the past eight years, and have always worked in accordance therewith. During that time I have never been baffled by the crazing difficulty, and I believe this success is due to the merits of the theory. My researches may not have extended far enough to discover the flaw in it, if there be one, and even should there be one, the theory has been very far ahead of no theory, as is evidenced by my experience. It is this theory I purpose to advance, with the hope that it may be of some assistance to the craft I am unable to lay down any iron-clad rules, on account of the extreme variations in clays used for bodies, but will give the deductions from nineteen years' experience, and hope to be able to put it before my readers in such a way as to be practical. It is much to be regretted that the secretive spirit, mentioned previously, exists. Had I had access to articles on this subject my nineteen years of work would probably have been productive of more valuable results. As it was, I had to start with almost no light and make It for myself as I went along. For eleven years I was working entirely in the dark, without principle or guide, and it was an extremely slow and discouraging way of working. During the last eight years my advance has been much more rapid, and results obtained have been certainties.