Sizing paper reduces the absorbency of the sheet and is usually only required when printing or painting with oil colour on paper. On the other hand, priming paper can change the colour, texture or absorbency of the sheet and prevents the oil from oil paint being absorbed, which is necessary to stop the pigment being left underbound on the surface.
Sizing paper
Size: Either rabbit skin glue or gelatine is recommended, under Oil Painting Primer. Use a dilution of 5g to 142ml of water and soak it before dissolving by warming. Vegetarians may prefer to use a cellulose size like wallpaper paste, but its sizing abilities are not as good. Diluted acrylic emulsion can be used under acrylic primer, but is generally unnecessary.
Procedure: Ideally the paper should be stretched and dried beforehand to prevent cockling. Papers that are already externally sized will only need one coat of size, whereas internally sized sheets should have two coats of size, with the first allowed to dry thoroughly before the second is applied.
Priming paper
Priming paper changes the colour, texture or absorbency of the sheet and can be done with acrylic primer, acrylic colour or a mixture of both. For oil colour however, a thin coat of undiluted Acrylic Gesso Primer is recommended. If an oil primer is required for oil colour, rabbit skin glue should be underneath. Oil paint is completely stable when painted on properly prepared paper; any weakness of oil on paper would be due to the lack of rigidity in the sheet versus a board or canvas.
Procedure: Ideally the paper should be stretched and dried beforehand to prevent cockling if a lot of moisture is involved, and we recommend using as good a quality primer as possible. It’s important to start with a good quality surface, as poor priming can’t be resolved later during your painting.