Sizing is used in paper making to change the absorption and wear characteristics of the materials; it is conventionally used as a surface preparation for some art techniques or gilding by artisans, painters and artists.
Precious Pieces uses natural sizing materials such as a mixture of collagen and myoban alumstone to improve the surface strength, water resistance and wet strength of the washi parchment. The sizing agent covers the cellulose and forms a film which is water-repellent.
All parchment can be made with internal or surface sizing treatments.
There are two types of sizing: internal sizing, sometimes also called engine sizing, and surface sizing (tub sizing). Internal sizing is applied to almost all papers and especially to all those that are machine made, while surface sizing is added for the highest grade bond, ledger, and writing papers.
Internal sizing (saizu):
Wet strength Internal sizing used in papermaking at the wet vat. By making the paper web more hydrophobic, the sizing agents influence dewatering and retention of fillers and fibers in the paper sheet. Next to paper quality, internal sizing agents’ main effect is on runability of the paper machine.
Surface sizing (do-sa biki):
Surface sizing solutions consists of mainly modified starches or sometime other hydrocolloid as gelatine and a surface sizing agent. Surface sizing agents are amphipathic molecules, having both hydrophilic (water-loving) and hydrophobic (water-repelling) ends. The sizing agent covers the cellulose and forms a film, with the hydrophilic tail facing the fiber and the hydrophobic tail facing outwards. This creates a water-repellent situation. Sizing improves the surface strength, printability, and water resistance of the paper surface. In the sizing solution, optical brightening agents (OBA) may also be added to improve the opacity and whiteness of the paper surface.