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. [Illustration: FIG. 16.--A Supercalender.] The amount of polish imparted by this plate-glazing process, as it is termed, can be varied considerably. With a light pressure and few rollings, the sheet of paper can be turned out having a fairly smooth surface, and without a conspicuously shiny appearance. By employing a great pressure and repeated rolling a much higher surface is attainable. If the plates are hot a still higher finish is possible. Machine-made rag papers are glazed usually by means of the supercalender, which is a stack of alternate steel and paper rolls placed one above the other in a vertical position. The reel of paper passes between these rolls and becomes highly surfaced. This operation effects many changes in the paper, besides imparting a good finish. The thickness of the sheet is reduced by about 40 per cent., the fibres being compressed much closer together. The tensile strength of the paper is also materially increased, and in every way the paper is improved. Moderation is essential in this as in everything, because excess of glazing weakens a paper, rendering it brittle and liable to crack when folded.