Painting Techniques: Oil, Acrylic and Mixed Media
This domain examines film-forming media: how a binder dries, how layers bond, and how incompatible layers fail. The exam rewards precise technical vocabulary (fat over lean, impasto, veladura, alla prima) applied to real decisions.
Oil
- Binders: linseed (strong, yellows), walnut and poppy (paler, slower). Diluents: turpentine or white spirit. Mediums: stand oil, damar varnish, alkyds.
- Fat over lean: each successive layer must contain more oil and less solvent and dry more slowly than the one under it, so the upper film stays flexible and does not crack over a shrinking lean layer.
- Techniques: impasto (thick, loaded), scumble (thin opaque dragged over a dry layer), glaze (transparent dark over light), alla prima (wet-in-wet, finished in one session).
Acrylic
- Polymer emulsion that dries by evaporation in minutes: fast, water-thinnable, permanent, and flexible.
- Mediums extend working time (retarder), change sheen (matte/gloss), or add body (modelling paste).
- Acrylic is a safe underpainting under oil once fully cured; acrylic over oil is unreliable because the oily film rejects water-based adhesion.
- Colours shift slightly on drying and the film darkens less than oil yellowing would.
Mixed media
- Rules of compatibility: water-based layers over solvent-based films only after full cure; wax and oil resists repel water media (useful as a reserve); collage needs acrylic medium, not gum.
Worked example
Plan a three-layer oil portrait. Layer 1: a lean, solvent-thinned imprimatura and block-in. Layer 2: re-state shapes with a little linseed medium added. Layer 3: impasto highlights and a transparent glaze in the shadows. Reasoning: solvent falls, oil rises, so drying slows and adhesion holds from the bottom up.
Marks-losing traps
- Inverting the rule and putting a lean layer over an oily one, which cracks and wrinkles.
- Using linseed oil as a thinner in the first layer.
- Varnishing before the film is fully cured (months, not days, for thick paint).
- Mixing oil and acrylic directly instead of layering them.
- Losing the drawing by overpainting every area to the same finish.