Sizing

Internal sizing

Usual internal sizing chemicals used in papermaking at the wet end are alkyl ketene dimer (AKD) and alkyl succinic anhydride (ASA) in neutral pH conditions, and the more ancient rosin system which requires acidic conditions and is still used in some mills.

Preservation

While sizing is intended to make paper more suitable for printing, acidic sizing using rosin also makes printing paper less durable and poses a problem for preservation of printed documents.

Sizing with starch was introduced quite early in the history of papermaking. Dard Hunter in Papermaking through Eighteen Centuries corroborates this by writing, "The Chinese used starch as a size for paper as early as A.D. 768 and its use continued until the fourteenth century when animal glue was substituted." In the early modern paper mills in Europe, which produced paper for printing and other uses, the sizing agent of choice was gelatin, as Susan Swartzburg writes in Preserving Library Materials': "Various substances have been used for sizing through the ages, from gypsum to animal gelatin." Hunter describes the process of sizing in these paper mills in the following:

The drying completed, the old papermakers dipped their paper into an animal size that had been made from the parings of hides, which they procured from the parchment-makers. It was necessary to size that paper so that it would be impervious to ink, but sizing was more needed in writing than in printing papers. Many books of the fifteenth century were printed upon paper that had not been sized, this extra treatment not being essential for a type impression. The sizing was accomplished by a worker holding a number of sheets by the aid of two wooden sticks, and dipping the paper into the warm gelatinous liquid. The sheets were then pressed to extract the superfluous gelatine. This crude method of sizing the paper was extremely wasteful as many sheets were torn and bruised beyond use. The sizing room of the early paper mills, was, for this reason, known as the 'slaughter-house'.

With the advent of the mass production of paper, the type of size used for paper production also changed. As Swartzburg writes, "By 1850 rosin size had come into use. Unfortunately, it produces a chemical action that hastens the decomposition of even the finest papers." In the field of library preservation it is known "that acid hydrolysis of cellulose and related carbo-hydrates [sic] is one of the key factors responsible for the degradation of paper during ageing." Some professional work has focused on the specific processes involved in the degradation of rosin-sized paper, in addition to work on developing permanent paper and sizing agents that will not eventually destroy the paper. An issue on the periphery to the preservation of paper and sizing, is washing, which is described by V. Daniels and J. Kosek as, "The removal of discolouration ... in water is principally effected by the dissolution of water-soluble material; this is usually done by immersing paper in water." In such a process, surface level items applied to the paper, such as size in early paper making processes as seen above, have the possibility of being removed from the paper, which might have some item specific interest in a special collections library. With later processes in paper making being more akin to "engine sizing," as H. Hardman and E. J. Cole describe it, "Engine sizing, which is part of the manufacturing process, has the ingredients added to the furnish or stock prior to sheet formation," the concern for the removal of size is less, and as such, most literature focuses on the more pressing issue of preserving acidic papers and similar issues.

Gilding

Sizing is a term used for any substance which is applied to a surface before gilding in order to ensure adhesion of the thin gold layer to the substrate. Egg whites have often been used as sizing; the Ancient Egyptians sometimes used blood. Other commonly used traditional materials for gold leaf sizing are rabbit-skin glue diluted and heated in water (water gilding), and boiled linseed oil (oil gilding); modern materials include polyvinyl acetate.

Textile warp sizing

Textile warp sizing, also known as tape sizing, of warp yarn is essential to reduce breakage of the yarn and thus production stops on the weaving machine. On the weaving machine, the warp yarns are subjected to several types of actions i.e. cyclic strain, flexing, abrasion at various loom parts, and inter yarn friction.

With sizing, the strength—abrasion resistance—of the yarn will improve and the hairiness of yarn will decrease. The degree of improvement of strength depends on adhesion force between fiber and size, size penetration, as well as encapsulation of yarn. Different types of water soluble polymers called textile sizing agents/chemicals such as modified starch, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and acrylates are used to protect the yarn. Also wax is added to reduce the abrasiveness of the warp yarns. The type of yarn material (e.g. cotton, polyester, linen), the thickness of the yarn, and the type of weaving machinery will determine the sizing recipe.

Often, the sizing liquor contain mutton tallow. Mutton tallow is an animal fat, used to improve abrasion resistance of yarns during weaving.

The sizing liquor is applied on warp yarn with a warp sizing machine. After the weaving process, the fabric is desized (washed).

Sizing may be done by hand, or in a sizing machine.

Canvas sizing for oil painting

Preparation of canvas for the oil painting always includes sizing: the canvas will "rot" if directly exposed to the paint. Aqueous glue, frequently the hide glue was used for sizing the canvas for centuries, Size in art is not a replacement for ground: it is not intended to form a level surface for painting, it is used to simply fill pores and isolate the canvas from the actual ground.