Kaolin and its preparation

The Manufacturer and builder 9, 1880

At a late meeting of the United States Potters' Association, a committee on raw material made a report, in which they referred to a want of uniformity in the preparation of the clay or other material before sending it to the potteries, and also to the necessity of having the raw material, wherever found, carefully analyzed. The report further states that the committee visited the clay mines in Chester and Delaware counties, Pennsylvania, and several in the State of Delaware, and found, to their surprise, immense deposits of fine, pure kaolin clays, that, if properly worked and developed, will furnish clay enough to last all the potteries in this country for a century. These pits, when opened, were worked in a wasteful and slovenly manner; but a change has been made in this respect within the past two years, by the introduction of improved machinery, by which the clay will be furnished free from iron and other impurities.

When the kaolin is taken from the earth at these mines it looks like lime, and quite solid, and, after being loosened and broken up, is shoveled into a hopper, through which it passes into a receiver. This receiver is a box, about 15 feet long, and from 2 to 3 feet high and wide. Through this box runs an iron shaft, having projections at intervals like blades of a knife. as the shaft revolves water is admitted into the box, thus dissolving the lumps, and, with the assistance of the blades, reducing the clay to powder, and leaving the receiver in the form of a whitish liquid. In this condition it is passed through a sand trough some 12 feet long, a current of water keeping it in motion and at the same time allowing the sand in the kaolin, which is the heaviest, to settle in the bottom of the trough. The liquefied kaolin is carried on and back and forth through boxes, where the mica is separatef from the kaolin, a process more difficult than getting rid of the sand, as the mica is much lighter. After this process is completed, the still liquefied kaolin is passed through very fine gauze screens, which have the effect of rendering the substance still more pure. From the screens it is conveyed into large tanks or vats, where it remains about twelve hours. When it is found that the kaolin has settled at the bottom, wth the water on the top perfectly clear, the waer is frawn off and the kaolin transferred, by means of pumps, to hydraulic presses. These presses are each about 12 feet long and 6 feet wide, the bottom being lined with zinc. Each press contains 34 leaves, having small opening between them, in which linen bags are placed to received the kaolin. The leaves are kept in their places by iron rods, and when the openings are filled the pressure is applied with sufficient force to remove all the water and leave the kaolin in a compact from in the bags. When the leaves are opened, the clay is found in cales 6 feet long, 22 inches wide and 3/4 of an inch in thickness. From the presses the clay is put in an open shed, or in the open air when the weather is hot, for thorough drying; then it assumes a nice whitish color, and is ready for shipment.