September 26, 2023 | Quality Control
What appliance makers fear is not an ugly colour — it is two units side by side that visibly differ. Once colour drift reaches a batch, rework costs far more than the paint ever saved.
| ΔE | What the eye sees | Where it is acceptable |
|---|---|---|
| ≤ 1.0 | Essentially indistinguishable | Adjacent panels on one unit |
| 1.0 – 1.5 | Noticeable on close comparison | General appliance exteriors |
| 1.5 – 3.0 | Visible side by side | Most customers will object |
| > 3.0 | Clearly a different colour | Batch rejection risk |
As a rule, adjacent panels — a fridge door next to its side — should sit at ΔE ≤ 1.0; up to 1.5 between separate parts is usually accepted. Put the number in the contract, or acceptance becomes an argument.
Paint lot. The same RAL code still varies in pigment dispersion between batches. Most often blamed, least often the real cause.
Oven temperature and line speed. Different cure means different depth of the same colour — hotter or slower runs darker. This is the most common source in practice.
Film thickness. Going from 18 μm to 22 μm shifts both opacity and hue, most visibly on light colours.
Substrate tone. Zinc, galvalume and Zn-Al-Mg have different base colours that thin coatings cannot fully hide — small effect on dark shades, large on light ones.
1. Retention samples. Keep an A4 panel from every batch marked with lot, date and film thickness, one set each side. Physical evidence ends arguments that data alone does not.
2. First-off check across batches. Compare the first panel of a new batch against the retention sample before running the coil. Stop and adjust rather than discovering it at the end.
3. Consolidate orders. Book the colour for a model in one go where possible, so panels that end up on the same unit come from the same batch.
4. Agree on a physical standard. A RAL code is a starting point, not a specification. The signed physical sample is what both sides measure against.
Colour tolerance is negotiable — but only as a number you can measure. Between "close enough" and "exactly the same" sits one ΔE value and the price of a spectrophotometer.
