Fig. 15.—Apparatus for Sizing Paper in continuous Rolls.
Sizing the Paper.—The dried paper as it leaves the loft is termed Waterleaf because, being unsized, it readily absorbs water, and therefore before it can be used it must be sized. For this purpose it is dipped into a solution of gelatine, an operation described as tub-sizing or animal-sizing, the former term being used on account of the tub in which the size is kept, and the latter on account of the fact that the gelatine is made from animal matter such as hides, cartilage, hoofs, and other refuse.
Animal Size.—This is prepared from hide pieces, skins, and the like by a simple process, which, however, requires a good deal of care in order to obtain the best results. The material is first thoroughly washed in plenty of clean water, and then heated with a definite quantity of water in a steam jacketed copper pan. The pieces slowly dissolve until a solution of gelatine is produced, and after the dirt and impurities have settled to the bottom of the pan the clear liquid is drawn off into store vessels. There are many details of a technical character to be attended to in the manufacture of good gelatine, and as the process is expensive, considerable attention is demanded at this stage in the completion of a sheet of paper.
The dry sheets of paper are sized by the simple expedient of dipping, or by the passage of the paper through a long trough. In the first case the workman takes up a number of sheets and dips the bunch into a vat of size at the proper temperature, about 100° Fahrenheit. He then allows the surplus size to drain off, and the sheets are submitted to a slight pressure in order to remove the excess of gelatine that will not drain off.
In the second case a different method is adopted in that the sheets of paper are carried by travelling felts through a bath of heated size, the excess gelatine being removed by the action of rubber or wooden rollers through which the papers are passed before leaving the apparatus. The papers are quickly and evenly sized by this method, which is now most generally used.
Glazing.—When the sheets of paper are quite dry they are ready for glazing, a process which turns the dull rough surface of the sized sheet into a highly polished smooth surface fit for use. The sheets are placed singly between copper or zinc plates, and a pile of these passed several times through heavy iron rollers, great pressure being applied to the latter during the operation.
