THE ART OF THE TILE-MASON
First of a series of articles on the designing, manufacturing and laying of clay tiles by "Ceramico”.
It is not considered necessary, in this series of articles dealing with the work of the tile-mason, to discuss at very great length and detail the manufacture of the tiles that he uses. The study of the manufacture of pottery, of which tile- making is a part, is very great and complex and no useful purpose can be served by discussing it in anything but the briefest of detail in any article or series of articles dealing with the tile-mason and his work. Indeed, very few tile- masons themselves possess more than a very rudimentary knowledge of the tiles which they use.
However, in order to get a good grasp of the tile-layers' art it is necessary to know something about the tiles, whose use we are about to describe, in the exterior and interior decoration of buildings.
There are, of course, many types of tiles which we will describe in brief detail later, but let us start first of all with the six inches by six inches, white glazed tile, which is used more universally than any other. It must be clearly understood that we give only the basic principles of manu- facture and any figures that we give are fair average only as each manufacturer has his own pet theories about what to do so that he may possibly get something a little better, some- how, than his contemporaries.
The raw materials that go into the making of the white six-by-six are as follows:-
Flint
40%
Ball Clay
28%
China Clay
2242
Cornish Stone
10%
To describe these materials briefly, one by one, flint is fuse resisting, is intensely white (after passing through the furnace), and prevents excessive contraction in the whole during firing. It consists of ordinary seashore boulders, which are fired by special methods in a specially constructed kiln, in which the temperature reaches 1,100 degrees Centigrade. This intense heat causes the flint to become very brittle and pure white all through. It is then ground, with water, for approximately twenty-four hours, great skill being required to know exactly when sufficient fineness has been obtained.
The experts believe that the best ball clay in the world is found in Dorsetshire, England and, according to geologists, this has been carried there, over the centuries, by the movement of water in the form of rivers etc. It consists of decomposed rock formation which is now quite a distance beneath the earth's surface and therefore has to be mined or at least quarried, after which it is laid out in the open to "weather". It is then "blunged" up with water until a milky liquid of the required consistency is obtained. Ball clay in the body of the tile gives hardness and density.
China clay, as most people understand, is the king of clays, is a basic constituent of all clays, and is obtained from decomposed granite formations. Streams of water are played over the granite and the mixture thus obtained runs steadily for quite a distance-as much as two or three miles over a vast network of settling tanks. At this stage of the process there are various solid bodies traversing the "milky way" along with the china clay, but since the latter is lighter than any of them it remains in suspension until it reaches the final series of tanks where it is trapped. It is then dried before despatch to the tile factory, where it is churned up in the same way as the ball clay. China clay gives to the tile body, whiteness and stability.
Everyone knows what Cornish stone is. This is ground down to a fine powder and mixed with water like flint.
Hardness, density, and the ability to fuse at the proper temperature, are the contributions of this latter to the tile body,
It can readily be seen that in these four ingredients the manufacturer has a sound basis for an exceptionally fine product. Where one ingredient lacks another compensates,
A laundry house maxim is "out of the blue comes the whitest wash" and, in like manner, the tile manufacturer, to ensure perfect whiteness, throws into his mix a pinch of cobalt oxide, 0.05%.
There are two methods of working the mix, wet and dry. In the first case the ingredients, all in a state of suspension in water, have their respective weights adjusted to a pint measure and are then poured into a tank in their proper pre-determined proportions. After mixing a thick white liquid results which is known to the trade as "slip."
The dry method is merely the mixing of the ingredients in the dry state with the water being added afterwards but this method can never be quite as accurate as the other because of the different water content in each of the raw materials.
taken
After mixing the slip is sieved very carefully and is then over beds of electro magnets in order that metal particles might be removed.
In every process up to now the presence of water has been merely to facilitate the smooth working of the operation and now, it's object having been accomplished, this water is to be removed.
This is done by pumping the slip through closely woven canvas sheets that are held in position by wooden or metal frames. Slabs of waterless slip are held between the frames and the water gets away.
These slabs are then dried by placing in a steam heated drying room after which they are ground down very finely Indeed until they become nothing more than dust. Thus, all the ingredients mentioned are now part of this dust and are ready to exert their induence in the forming, out of this dust, a sound six inches by six inches white glazed tile.
The dust is formed into tiles by pressure in a crew press, Some of these presses are worked by hand and some are worked mechanically but a lot of tile-makers still swear by the hand operated ones believing that the process of making a perfect tue depends, to a large extent, on the touch of the skuled operative.
The tile is made slighty larger than the actual size that is required for the simple reason that it is to undergo two severe firing process, "biscuit" and "glost" during which it will shrink. The skill, of course, comes in knowing how much a budy of certain percentages of ingredients will shrink under what heat.
The tile, pressed out of dust and still unfired clay, can be handled but must be done so very carefully. It has rough edges which must be got rid of and this process of putting a finish to the unfired tile is called "tettling". After fettling the tiles are formed into bungs, put onto wooden boards and placed into drying chambers.
The next thing to happen is the biscuit firing. The tiles, a few at a time, are bedded snugly in sand in a receptacle known as a saggar which is made of fireclay and is highly refractory. Now, the saggars containing the tiles are placed into a specially constructed kiln or oven in which the heat is gradually stepped up over a period of approximately seven days. The maximum heat reached is 1,150 degrees Centigrade. The cooling off, though not taking so long has to be carefully carried out too and the whole process of firing and cooling requires great skill and is therefore a well paid job.
We have now a biscuit tile but, notwithstanding the great care and skill that has already been used up to now we shall not And them all perfect. This is where the sorters come in and these people with great dexterity speedily sort out the wheat from the chaff.
SOFTWOOD and HARDWOOD LOGS and PLANKS
I
Kapoh
Seraya Poonah Merbau
416 BEACH RD., SINGAPORE MILLS: SINGAPORE,
KEMAMAN & MALACCA.
Keruing
Jelutong
etc.
Kempas Balau Chenghai
Large stocks available for immediate delivery Samples and quotations gladly submitted on request
CHYE HIN LIMITED.
GENERAL TIMBER MERCHANTS & SAWMILLERS TELE: NOS:-7877 & 7878.
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AGENTS IN H. K. THE SINGAPORE SAWMILL LTD., 344 LOCKHART RD.
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