Paint Mixing and Color Matching
What the exam expects
Know the mixing system: basecoat, reducer, hardener, and additive ratios by volume, and why ratios matter. Understand pot life, induction time, and recoat windows. Color matching questions test your knowledge of variant selection, spray-out cards, blending, and the effect of primer color and gun technique on final appearance.
Core concepts
- Mix ratio: expressed as base : reducer : hardener (e.g., 4:1:1). Always measure by volume with a graduated stick; never eyeball.
- Reducer selection: temperature-based (fast, medium, slow). Hot weather needs slower reducer; cold needs faster.
- Color variants: manufacturers list alternates for the same code because of plant and batch differences. Spray a test card, compare under proper light, then choose the variant.
- Metallic/pearl control: orientation and gun distance affect flake lay; a drop coat or control coat helps blend.
- Blending: fade color into adjacent panels; do not stop at a hard panel edge.
Traps
Questions may tempt you to "add reducer to stretch color" - that changes viscosity, coverage, and color. Another trap: matching color under fluorescent shop light instead of daylight or a color-corrected lamp. Also, primer color affects metallic topcoats more than solid colors.
Worked example
A door is painted with the OEM code but does not match the fender. The technician should spray a variant card of each listed alternate, compare in daylight at multiple angles, select the closest variant, and plan to blend into the fender rather than repaint the whole side.
Rule of thumb: measure ratios by volume, match under daylight, and always plan a blend.