Pigments and Media
This domain tests what paint actually is, how pigment properties affect handling, and how to select a medium for a design job. Expect pigment classification, opacity/lightfastness, support preparation and safety.
Core rules
- Paint = pigment + binder. The pigment supplies colour and many handling properties; the binder supplies film, gloss and drying behaviour.
- Earth pigments (ochre, sienna, umber) are cheap, opaque and lightfast. Mineral pigments include ultramarine (natural lazurite; synthetic from the 19th century), viridian and cadmiums. Synthetic organic pigments include phthalo, quinacridone and azo colours, often transparent and strongly tinting.
- Key properties: opacity/hiding power, tinting strength, transparency, lightfastness (ASTM I–V), staining and granulation.
- Watercolour uses gum arabic and relies on transparency and the white of the paper. Gouache adds chalk for opacity. Poster colour is an opaque, economical design medium. Acrylic is a polymer emulsion that dries quickly and can be used on many supports. Oil uses a drying oil and needs a primed support.
- Paper weight (gsm), surface (cold-press, hot-press, rough) and priming change the result.
- Cadmium, lead and cobalt pigments are toxic; avoid ingestion, use ventilation and keep solvents away from skin.
Worked example
A prospectus cover needs flat, bright, reproducible shapes. Choose acrylic or poster colour rather than watercolour: opacity gives even flats, and acrylic binds well to board. Apply two thin coats rather than one thick coat to avoid cracking. Test the scanned colour against a printed proof, because saturated oranges and greens often shift. Avoid metallic or fluorescent pigments if the cover must match a CMYK proof. The reasoning is job requirement → opacity and durability → reproduction.
Traps that cost marks
- Treating gouache as identical to watercolour; it is opaque and rewettable.
- Confusing “permanence” with lightfastness without naming the rating.
- Assuming “cadmium hue” contains cadmium; it is a substitute mixture.
- Using oil paint on unprimed paper or board.
- Ignoring pigment toxicity in a school practical answer.