Coating Systems and Colour Technology
Coating Systems and Colour Technology tests how paints are built, how they cure, and how colour and sheen behave on a job. Expect questions on binder-pigment balance, dry and wet film, tinting, hiding, and metamerism.
Coating composition and film formation
- A coating contains binder, pigment, solvent or water, and additives. The pigment volume concentration relative to critical PVC determines whether the film is glossy, semi-gloss, or flat and whether it has enough binder to protect.
- Waterborne coatings coalesce as water and cosolvent evaporate; alkyds oxidize and crosslink; epoxies and polyurethanes cure chemically. Recoat windows and pot life follow the product data sheet.
Colour and appearance
- Colour is described by hue, value, and chroma. Light reflectance value indicates how much light a colour returns; lower LRV absorbs more light and heat.
- Tinting uses colourants added to a base; the base must match the colourant system. Metamerism occurs when two colour matches look alike under one light source but differ under another.
- Sheen changes appearance and durability: flat hides defects, while satin and semi-gloss clean better in kitchens and bathrooms.
Worked example
A 18 L pail is tinted with 6% colourant by volume. Colourant volume = 18 × 0.06 = 1.08 L. If the base has an LRV of 85 and the colourant an LRV of 5, a rough weighted estimate is 0.94 × 85 + 0.06 × 5 = 80.2. The estimate is only a guide because colourants scatter and absorb light non-linearly, but it shows why small tint additions can move a light base substantially.
Traps that cost marks
Specifying a flat sheen in a washable area; ignoring metamerism when approving a custom colour; adding universal colourant incompatible with the base; and judging hiding from a wet sample rather than a cured drawdown all lose marks.
Key points
- Binder, pigment, solvent, and additives determine film properties.
- PVC relative to critical PVC explains sheen and durability.
- Recoat windows and cure chemistry come from the product data sheet.
- Metamerism and LRV affect colour approval.
- Tint only within the base and colourant system.