Grey scale colour difference check
A practical guide to grey scale colour difference check: what to check on site, what a photograph cannot establish, and what to write in your purchase specification.
Colour difference in furniture is described in words — "even colour throughout", "batch to batch consistent" — and almost none of those words are checkable. A grey scale value is checkable.
The grey scale
A grey scale card carries steps of known lightness difference. Under a defined light level, a panel and a reference card are compared and the difference step is recorded.
| Typical requirement | What it means in practice |
|---|---|
| Grey scale 4 or better | Residential orders. Acceptable visible variation within a batch. |
| Grey scale 5 or better | Contract and hospitality work. Visually matched under normal lighting. |
| ΔE ≤ 1.0 | Instrumental measurement, used where a contract specifies a numeric colour target. |
Why per-unit checking misses the defect
A spray line re-adjustment between shifts, or a lacquer batch change, produces two batches within one production run. Every chair in batch A matches the approved sample. Every chair in batch B also matches the approved sample. But A and B differ from each other.
The failure is in the batch relationship, not in any individual unit. Only a check that compares samples drawn from different positions in the run can find it.
How the check is done
- Sample units from the front, middle and rear of the batch
- Place them side by side under daylight, then again under raking light
- Record the grey scale reading against the approved sample
- Photograph the samples together in one frame, so the comparison is visible in the report
dining verification sets out where this sits in a dining furniture verification.
What to write in the specification
"Grey scale 4 or better, measured on samples drawn from the front, middle and rear of the batch. Any split above the stated value is a finding."
And at booking, tell the verifier whether your order is large enough to have crossed more than one production shift. It changes the sampling plan.
Common questions
What should my purchase specification contain?
Model and quantity, dimensions with tolerance, materials named rather than described generically, colour standard with a grey scale value, and any standard the goods must meet.
How early should verification happen before shipment?
After production is substantially complete but before the container is sealed. Earlier and there is nothing to inspect; later and the remedy is to unload in China rather than in your own country.
What does AQL mean in furniture inspection?
AQL is the Acceptable Quality Limit under ISO 2859-1 — the quality threshold used to accept or reject a sampled lot. It is an input to a decision, not a statement about how good the goods are.
Verifying a furniture order?
We check your goods at the factory against your PI, your agreed specification and your approved sample. Three levels, published prices, report within 24 hours.