C.S.O. 13 in 3752/19.
65
HONG KONG,
GEOLOGICAL SURVEY OF THE COLONY.
REPORT ON CLAYS FROM CERTAIN DISTRICTS.
No. 1929
6
Clay and Kaolin from Hong Kong.
The samples which are the subject of this report were sent to the Imperial Institute by His Excellency the Governor, Hong Kong, and referred to in his letter of the 8th December 1927.
It was required that the materials, which had been forwarded at the request of Dr. R. W. Brock, Dean of the Faculty of Applied Science, University of British Columbia, should be tested as to their suitability for higher-grade clay products and wares.
Results of Examination.
White Clay.
The sample consisted of 31 lb. of a fairly soft whitish clay, in the form of small lumps. It was of rather poor plasticity when mixed with water.
Pottery trials.
Unwashed clay. For use in these trials a quantity of the clay was ground to pass a sieve containing 120 meshes per linear inch. It was noticed that the material was easy to grind and that no clogging of the mill took place. An attempt to mould thin-walled vessels from the ground clay proved unsuccessful, the clay being only slightly plastic and having practically no binding power. The formation of pieces of a less fragile nature by pressing the moist clay in plaster moulds was somewhat easier, but the unfired ware was extremely weak and very difficult to handle. It was thought that finer grinding might pos- sibly improve the working properties of the clay, and a further quantity of the sample was therefore ground to pass a sieve having 180 meshes per linear inch. Trials with this finer material showed that, although a certain amount of improvement was effected by this treatment, the clay was still deficient in plasticity and would not be adapted for moulding by the usual methods.
Washed clay. A quantity of the raw clay was roughly crushed to about 4′′ mesh, and then blunged in a laboratory washing mill with about five times its weight of water. On account of the comparatively fine nature of the impurities contained in the raw clay, it was found necessary, in order to ensure that the impurities were thoroughly freed from clay, to reduce the rate of flow of the clay and water entering the blunger below that which could be successfully employed when washing a crude kaolin. After leaving the blunger the slip was allowed to settle and the separation of clay from the impurities was thereby effected. It was found that this separation was somewhat difficult on account of the fine state of division of the non-clayey particles.
The results obtained from this test showed that the crude material yielded 56.6 per cent of clay, and 43.4 per cent of residue.
The washed clay was of a fairly-good texture and colour, though not dead white: It worked well in all the tests to which it was submitted. The residue consisted mainly of kaolinized felspar and a little quartz.