The process by which gelatin rosin, starch or other synthetic substance is added to paper to provide resistence to the absorption of moisture or eliminating ink feathering and bleed through. Sizing added to the beater or vat of pulp is known as internal sizing. Sulphite pulp is produced from the wood of coniferous trees. Wood chips are cooked in calcium bisulphate or sodium sulphite, and bleached, producing fairly long strong fibers. Since the end of the 1860' s until recent years, it has been the most widely used pulp in America.
Sulphite pulp is available in a range of grades up to pure alpha cellulose.
Vellum is also used to designate heavy weight, translucent drawing of drafting papers. The translucent design or name easily visible when a sheet is held to the light. A design is sewn onto the papermaking screen with raised wire. When the sheet is formed, the pulp settles in a thinner layer over the wire design. The continuous ribbon of paper, in its full width, during any stage of its progress through the paper machine.