Resins

Two types of resin were regularly used in early modern manuscript production, mainly to temper ink or colors and to size printed paper.

Gum arabic
Gum arabic, a resin derived from the acacia tree (esp. Acacia arabica), was long a standard ingredient in iron-gall inks, ideal for its thickening and binding properties. Although it lengthens drying time for inks on the page, as a binding agent it prevents ink from seeping too diffusely into porous writing materials such as rag paper (a hazard known as 'feathering'). Its thickening effect on the ink also improves viscosity and flow rate, and helps to suspend any added colorings. Although once used as an adhesive for paper, these days it is mostly widely employed as a thickener and emulsifier in soft drinks, and as a stabiliser in marshmallows.

Gum sandarac
Gum sandarac is a resin derived from the sandarac or avar tree (Tetraclinis articulata, or Callitris quadrivalvis), a conifer related to the juniper, most commonly found in north-west Africa. A hard and highly brittle resin, gum sandarac has long been used to make pounce and varnishes. Early modern scribes would have used gum sandarac, in combination with pumice stone or ground cuttle-fish, to clean and prepare parchment for writing, or to treat unsized papers.