Oil Painting
Adhesion or Anchorage of Coatings

1. An absorbent or porous surface which will partially imbibe the paint vehicle.

2. A rough, textural surface [granular, fibrous, weblike, or scored] which will hold the dried paint in a mechanical grip or bond.

A slick, shiny, completely nonabsorbent surface is the least likely to offer permanent adhesion. A coating that is too absorbent is generally not desirable; for example, an unsized gesso coating with full absorbency may take watercolor and tempera very well, but it will absorb so much of an oil vehicle as to leave the paint in a weak condition, a development more likely with heavy, thick coatings than with thin or very thin coats. Extreme absorbency can be reduced by the use of a size, as previously mentioned.

As a general rule, a combination of the proper degree of tooth plus the proper degree of absorbency is desirable. However, for some painting methods that coarseness of texture of a nonabsorbent ground or the absorbency of a smooth ground will alone suffice to promote good adhesion of the surface coating to the support.

A common cause of poor adhesion and of the development of various defects through weakening of the paint film is the use of stale oil colors--blobs of color that have been too long exposed to air on the palette, where they have begun to go through their drying action and have thickened. Painters who "freshen" such colors by adding turpentine to them delude themselves; the thickened oils have already gone though their sticky, adhesive stage [p. 103] either partially or wholly while on the palette, and they have little or no chance of equaling the adhesive power or film strength of fresh colors. [pp. 103-104]