SELECTING AND PREPARING THE CLAYS.-" WEATHERING." " First in order we will try and give you our ideas on the se lecting and preparing of the clays or raw material to be used in the manufacture of pressed brick. Of course all sections of the country do not have just the right kind of materials that will produce a first-class pressed brick, and where clays are found suitable for the purpose, they will differ very much in their natures in one locality from what they are in some others, and therefore the manufacturer in selecting and preparing his ma terials is compelled to be governed according to circumstances, that is, he must make the best use of what different materials he may have at hand, for the reason that pressed brick as well as other building brick will hardly permit, or will pay well enough to allow the shipping of the clay any great distance. Now, although the burning of pressed brick is the last process which the clay goes through before being finished into pressed brick, it is about the first step to be taken into consideration. In selecting and preparing our raw materials we must first know what the brick that are to be made from them will be when burnt, or else all of our work at the start will be of no use ; and I think all of you will agree with me when I say that to prepare materials that will make a good pressed brick in a raw or green state is but very little trouble, but to get at what kind of ma terials will make a perfect pressed brick after it has gone through the test of firing requires much care and study ; and we think that the only way, or at least the best way known to us at present how to combine materials successfully for the making of good pressed brick is by a practical experience, that is by the making of different trials and experiments with whatever kinds of clay, loam or sand that the manufacturer may have at his command.
" Of course a chemical analysis of clays is all right as a matter. of theory, but where so much raw material is required to be used as is the case in the manufacture of brick ; I think that the knowledge and experience gained by practical working is by far the best ; of course it requires time and expense to get this kind of experience, but it will certainly pay the manufac turer the best in the long run.
" Some of the main points to be considered in combining materials for pressed brick is to get a combination that will stand enough firing to produce a brick of sufficient hardness for all purposes without too much warping or shrinkage, and at the same time to retain a desirable color, as we often find that in using too much of a clay that will fuse or melt easily, the brick when burnt are warped and crooked and shrunk so much that they will be of many different sizes, those that are burnt the hardest being smaller than those that are not burnt so hard, and on the other hand some material will stand more firing and produce a brick that will be of a fair color and keep straight and of full size when burnt, but probably they will not be as tough and strong as are desired. Thus it happens very often
that by combining two or more materials together we get the results for which we are trying. There is such a wide differ ence in materials that one manufacturer may have at his com mand from what others may have, that there can be no set rule for the combining of materials for pressed brick, that will apply to every locality or that can always be followed with safety. The preparation and proper pugging or tempering of clays for pressed brick is quite an important matter, but with the improved machinery that has lately been brought into use for that purpose it can now be done with very little difficulty.
" The question of weathering clay before being used for the manufacture of brick is a thing that has been advocated always as beneficial. We claim that the benefits which a manufac turer will gain by the weathering of clays before using depends a great deal upon circumstances. In the first place, we do not think that a brick can be any better from having the clay ex posed to the weather for a long time than it can by using the clay direct from the bank, providing that the clay be thor oughly worked and mixed before being used.
" So you can see that what we mean by this is, that the weathering of clay is of no real benefit to the finished article, but will only lessen the labor and expense of mixing and pre paring of the clay before use.
"This matter, as well as some other points appertaining to the manufacture of pressed brick, must be governed according to circumstances. In some places the clays used are of a very stubborn and strong nature, and will not yield readily to the common methods used for tempering and mixing unless they are first exposed to the weather for a long time, and then they will yield very readily when the water is placed upon them for the purpose of soaking and mixing. It is much cheaper to expose material of this kind to the weather than it would be to use extra machinery for the purpose of reducing it to that state that. it can be worked by the ordinary methods used for temper ing. The majority of clays that are used for the manufacture of pressed brick can be worked at a reasonable cost of labor and expense without the process of weathering, and for these reasons we claim that it is much cheaper to use the material direct from the bank, and we think it can be done without in any way affecting the quality of the finished article.
" There is one expense attached to the weathering of raw material to be used in the manufacture of brick, besides the cost of the extra handling which is necessary, and that is in the percentage of loss to the materials by being exposed a long time to the elements. We have made some tests of what loss there is in weathering clay by digging it up in the early winter and letting it lie until the next summer before using it, which is about the period that it has been the custom for brickmakers in the eastern part of the United States to weather their clay, and we have found that the actual loss to materials has been fully fifteen per cent.