RAG STOCK.
Rag papers may be made from all sorts and conditions of rags, so the fineness of the finished product depends upon the newness and quality of the rags. New white cuttings from textile factories are the best, as their strength is unimpaired by previous use, and they may be prepared for manufacture with a minimum use of chemicals.
From this high standard, rags are graded down in accordance with their color, cleanliness and condition. The first sortings are made by stock-dealers, and the paper-maker orders whatever grades are suitable to his purpose. After their receipt at the mill, the bales of rags are opened, dusted by machine and distributed to girls, who sort them, open up the seams so as to release hidden dirt, remove buttons and other foreign material.
In the making of the highest grades, the new white rags are cut by hand into small pieces of uniform size, but ordinarily they are fed into a mechanical rag cutter. After this they are passed through a dusting machine to rid them as far as possible from dirt and foreign matter, which might otherwise appear as specks in the paper.
Boiling.—Dyes and greasy matters are associated with the fibers, and in order to obtain the pure cellulose fiber the rags are cooked, under steam pressure, in rotary boilers with alkali. This saponifies and dissolves the non-cellulose compounds, and the soda in combination with these soluble materials is subsequently washed out. The amount of steam pressure, the quantity of chemicals, and the duration of the cooking, are subject to variation under different conditions. At the conclusion of the process the manholes in the boilers are opened, and the contents are deposited on the floor, later to be transferred to the washer room.
Washing.—A washing engine consists of an oval tub about four feet high. It is divided longitudinally by a partition or “mid-feather,” with a passage left at either end for the circulation of the stock. On one side is located a large roll, having a continuous parallel series of knives horizontally inserted in its surface. The floor of the engine slopes gently to a point under the roll, where a bed plate is set. Behind the roll is a raised partition or dam, over which the stock is thrown as it passes between the beater roll and the bed plate. This is known as the “back-fall,” and assists in the circulation. The roll may be raised or lowered over the bed plate, and by this means the breaking of the stock is regulated.
Affixed to the tub are one or more washing cylinders, so arranged that they may be lowered into the stock. These are constructed in such a way that during the process of washing the water passes through their wire-covered surfaces and is drained into the hollow axle of the roll by an interior arrangement, called buckets. The axle, being open at one end, permits the wash water to escape.
At first the engine is partly filled with water, then the rags are gradually thrown in until the tub is full. The revolving roll keeps the mass in circulation, while the rags are broken and shredded as they pass beneath it. A continuous stream of fresh water runs into the tub, and in running out through the revolving washer drums carries off the dirt, but the fibers themselves can not pass through the wire coverings, so remain until cleansed. Necessarily the water used must be free from sediment or mineral impurities, such as iron, otherwise it would fill the stock with specks. Therefore, a filter plant is usually maintained.
Bleaching.—After the washing has been completed the drums are raised clear of the stock and bleaching liquor is introduced. This is an important step, and if not carefully managed may impair the stock. For instance, if bleaching is carried on at too high a temperature, the white color obtained will not be permanent, and discoloration will occur after the paper is made. Much of the paper, which at first displays a brilliant white color, will afterward take on a yellowish tinge, especially if it is exposed to light. A comparison between the century-old hand-made papers and modern “fine writings,” makes the old papers appear a “natural” shade, but place both for a few hours in the sunlight and often the modern paper will fade, whereas the old sun-bleached papers remain unaltered. The high artificial bleaching does not insure permanent results.
After the bleach liquor has been thoroughly mixed in, the stock is discharged into drainers and allowed to stand for a week or more, until no traces of chlorine remain. In this state the pulp is known as “half-stock.”
The treatment of hemp is so similar to that of rags that a description here of the process is superfluous.