China clay

“ The loading material used for ordinary qualities is kaolin, or china clay, and for the better qualities sulphate of lime or pearl hardening, as it is termed in the trade. China clay, as it occurs in commerce, is in the form of soft lumps and powder, is nearly white, and when rubbed between the finger and thumb should present no hard particles of gritty matter. To prepare it for mixing with the pulp it is first worked up into a thin cream with water, which is usually done in a vessel furnished with an agitating arrangement by which the clay becomes intimately mixed with the water. ”

“ The pottery and china clays are usually more free from accessory constituents, and are regarded as the 'purest' clays on the market, though a considerable amount of latitude must be allowed in interpreting the term 'pure.' China clays are by no means pure in the state in which they occur, and require careful treatment before they can be sold. ”

“ The men and women who handle the clay get the same stuff for nothing, and do well enough without the perfume. China clay, being a modern industry in this land of ancients, has no piskie, or nuggie, or bucca connected with it, and Guy took kindly to it on that account, saying it represented the practical, hard-headed twentieth century. ”

“ Owing to their extreme smallness it is exceedingly difficult to prove that they are not so, though for all ordinary purposes they may be regarded as amorphous, the proportion of obviously crystalline matter present in British china clay of the highest qualities being so small as to be negligible. ”

“ Clay is chiefly silicate of aluminum and other metals. Kaolin is its purest form. The properties of clay vary with its composition, as china clay, fire clay, pipe clay, brick clay. Clays are found in all parts of the world as a result of the decomposition of other rocks.
The location of manufacturing centers of pottery of all kinds and of bricks, is dependent on clay deposits. In pottery making, Ohio, New Jersey and Pennsylvania lead the United States. Abroad, fine china is made in France, Germany, Austria, England, Japan, and China.
[104-
107] ”

“ True fuller's earth is obtained chiefly from the neighbourhood of Reigate, Surrey, Woburn Sands, Bedfordshire and from below the Oolite formation near Bath, but owing to the scarcity of the material and the irregularity of its behaviour, china clay is now largely used for the same purpose. True fuller's earth is much more fusible than the white clays usually substituted for it, and when mixed with water it does not form a plastic paste but falls to powder. ”

“ A few of the most important clay rocks, such as china-clay, brick-clay, red-clay and shale, may be briefly described here.
China-clay is white, friable and earthy. It occurs in regions of granite, porphyry and syenite, and usually occupies funnel-shaped cavities of no great superficial area, but of considerable depth. It consists of very fine scaly kaolin, larger, shining plates of white mica, grains of quartz and particles of semi-decomposed felspar, tourmaline, zircon and other minerals, which originally formed part of the granite. ”

“ Where, however, decomposition of the granitoid rock has been exceptionally thorough, kaolin may be present in sufficient quantity to predominate over other materials. The product washed from the surface then gathers as a white clay even in lakes, and further artificial washing may extract from it an actual kaolin-earth or china-clay. In such cases, the rock has become rotted throughout in consequence of subterranean action. ”

“ Mellor and Holdcroft point out that there is no critical point of decomposition for clay substance obtained from china clay, as it appears to lose water at all temperatures, though its decomposition proceeds at so slow a rate below 400° C. as to be scarcely appreciable.
[15] Some clays are highly hygroscopic and absorb moisture readily from the atmosphere. According to Seger (7) this hygroscopicity distinguishes true clay from silt and dust. ”

“ In composition, ball clays appear to consist chiefly of a hydro-alumino-silicate corresponding to the formula H4Al2Si2O9, and in this they very closely resemble the china clays (kaolins) . The latter are, however, but slightly plastic whilst the ball clays are [65] amongst the most plastic clays known. The china clays are also much more refractory than the ball clays owing to the somewhat larger proportion of alkalies in the latter.
Pipe clays are an inferior quality of ball clay; they contain rather more iron and alkalies and considerably more silica. ”

“ Ever since the publication of Seger's memorable [148] papers (7) , and to a small extent before that time, it has been generally understood that china clay or kaolin represented the true essential constituent of clays, but several investigators have been so imbued with the idea that all true clay substance must have a crystalline form that they have frequently used the term 'kaolinite' to include the 'amorphous' substance in plastic clays. ”

“ It is commonly supposed that all clays are plastic, but some of the purest china clays are almost devoid of this property and some of the most impure earths used for brickmaking possess it in a striking degree. Shales, on the one hand—whilst clearly a variety of clay—are hard and rock-like, requiring to be reduced to powder and very thoroughly mixed with water before they become plastic; many impure surface deposits, on the other hand, are so highly plastic as to necessitate the [3] addition of other (sandy) materials before they can be used for the manufacture of bricks and tiles. ”

“ Simply and solely because the snake or worm WAS white. We are near the county of Stafford, where the great industry of china-burning was originated and grew. Stafford owes much of its wealth to the large deposits of the rare china clay found in it from time to time. These deposits become in time pretty well exhausted; but for centuries Stafford adventurers looked for the special clay, as Ohio and Pennsylvania farmers and explorers looked for oil. Anyone owning real estate on which china clay can be discovered strikes a sort of gold mine. ”

“ Usually, however, the most careful treatment fails to remove all these minerals; their presence [9] may then be detected by microscopical examination and by chemical analysis. For most of the purposes for which clays are used, small proportions of these silicates are unimportant, but where clays of a highly refractory nature are required; and for most of the purposes for which china clays (kaolins) are employed, [10] they must not be present to the extent of more than 5 per cent., smaller proportions being preferable. ”

“ Hard refractory clays often remain porous and are a fruitful source of crazing and breaking. The addition of flint or fine washed sand, finely powdered grog, or pitchers, or even refractory China clays, in quantities varying from about 5 per cent to 20 per cent, but settled only by repeated trials, will stiffen up or open out rich clays inclined to warp or burst. Rich fusible clays added to hard clays may stop the crazing, or the fusing point may be lowered by the addition of spar. Stiff gravelly clay will require finer sieving or repeated washing to rid it of some of the grit or sand. ”

“ China clays and kaolins are not appreciably affected by dilute acids, but some specimens are partially decomposed by boiling concentrated hydrochloric acid (26) and all are decomposed by boiling sulphuric [107] acid, the alumina being dissolved and the silica liberated in a form easily soluble in solutions of caustic soda or potash. This has led to the conclusion that some kaolins may have been produced by weathering, as the bulk of true kaolinitic clays (such as Cornish china clay) is not affected by boiling hydrochloric acid (p. 81) . ”

“ There are several kinds of filler in common use. The most common is China clay, of which the cleanest and finest grades are obtained principally in England. No equally good deposit has yet been successfully developed in this country. Clay is a product of the natural disintegration of feldspar. ”

“ The large whitewashed place was occupied by ungainly machines and receptacles through which the four sorts of clay used in the common 'body'—ball clay, China clay, flint clay and stone clay—were compelled to pass before they became a white putty-like mixture meet for shaping by human hands. ”

“ Mix four parts by weight of carbonate of soda with six parts of china clay, and grind this mixture in about eight parts of japan, thinning the product with turpentine or benzine to the consistency of linseed oil. Laundry starch may be used in place of china clay, giving a filler which is somewhat easier of application than the clay filler because it does not settle. It lacks in durability, however, especially if it is not well covered. The finest grained woods do not require the addition of any material to the filler to give body. ”

“ The soil of the mountains in the south of China is of the poorest description. Rocks of granite are seen every where protruding themselves above the scanty vegetation, whilst the soil itself is composed of dry burnt clay mixed with particles of granite in a decaying or disintegrated state. This soil naturally so poor, is kept so by the practice of periodically cutting and carrying off the long grass [Pg 293] and stunted bushes for fire-wood. Sometimes the natives set fire to this upon the mountains, for the purpose of affording a scanty manure, but nevertheless the soil is miserably sterile. ”

“ As ordinary clays are never quite free from metallic [156] compounds other than alumina, this formation of a fused portion—technically known as vitrification (p. 37) —occurs at temperatures depending on the nature of the materials present, so that a wide range of products is obtained, the series commencing with the entirely unfused pure clay (china clay) , passing through the slightly vitrified fireclays, the more completely vitrified ball clays to the vitrifiable stoneware clays and ending with materials so rich in easily fusible matter as scarcely to be worthy of the name of clays. ”

“ On some of the hills on the island of Amoy, the traveller may wander for miles and scarcely see even a weed. On every side there is nothing but masses of dark crumbling granite, and red burnt-looking clay. This, however, seems the northern boundary of the most barren part of China. When we reach the river Min near Foo-chow-foo, there is a great change visible in the vegetation of the hills, caused, of course, by the richer nature of the soil. This remark applies to the northern portion of Fokien and to the whole of the province of Chekiang. ”

“ This sort of clay, as I hinted formerly, is used to clay sugar; and the best sort of mugs are made with it, and the ingenious Mr. Daught of Fulham tells me that ’tis the same earth China-ware is made of, and ’tis made, not by lying long in the earth, but in the fire; and if it were worth while, we may make as good China here as any is in the world. ”

“ The glassy cement that holds the particles of lime carbonate shows as the glaze of the polished surface. It is silica. One sees the same mineral on the face of polished granite.
Clays are rarely pure. Kaolin is a white clay which, when baked, becomes porcelain. China-ware [Pg 34] is artificially metamorphosed kaolin. In the early rocks the clay beds were transformed by heat into jasper and slates. In beds where clay mingled with sand, in layers, gneiss was formed. If mica is a prominent element, the metamorphic rock is easily parted into overlapping, scaly layers. It is a mica schist. ”

“ These are much heavier than the quartz, feldspar and other ingredients of the soil, which vary from 2.6 to 2.7 and are washed away. Finally, there is the natural disinclination on the part of the Chinese to dig, from their belief that it is wrong to explore the soil, and this disinclination on their part has done much to prevent a better knowledge of the Stone Age, and our knowledge of the races which must have preceded the civilization of China; many facts of mining interest have been neglected, as well, on account of this prejudice. ”

“ The earth was worn away around everything, walls, trees, roadsides, monuments, those great slabs of stone, top-heavy with carved dragons, that may be seen anywhere; for great portions of China are half-desert, dry as dust, of a moistureless brown soil ready to wash or blow away at the least provocation, and slavishly dependent upon irrigation. Chinese farming methods, too, increase this erosion. Everywhere men were cutting off the top layer of soil and screening the earth into many little mounds that stretched in long rows across the sunken fields. ”

“ Fields of rice and the opium poppy were sometimes met with, but of the silk-worm and tea-plant, which furnish the great staples of the Chinese export trade, we saw absolutely nothing on our route through the northern provinces. Apart from the “Yellow Lands” of the Hoang-ho, which need no manure, the arable regions of China seem to have maintained their fecundity for over four thousand years, entirely through the thoughtful care of the peasantry in restoring to the soil, under another form, all that the crops have taken from it. The plowing of the Chinese is very poor. ”

“ They are not, however, exactly like the European implements, but have a character of their own. We do not yet know what the men of these communities looked like, because as yet no indisputable human remains have been found. All the stone implements have been found on the surface, where they have been brought to light by the wind as it swept away the loess. These stone-age communities seem to have lasted a considerable time and to have been spread not only over North China but over Mongolia and Manchuria. It must not be assumed that the stone age came to an end at the same time everywhere. ”