Measuring Shade: Delta E and the Tolerance

Shade approval is where a technically acceptable batch meets a buyer’s eye. “Too dark” and “not quite the same” are not specifications, and a spectrophotometer only helps if the tolerance and the method are agreed in advance. This note covers what Delta E measures, which tolerance is realistic, and how to prepare a sample that can be compared at all.

1. What Delta E is

Delta E is the numerical distance between two colours in a defined colour space, usually CIELAB. A value of zero means no measurable difference. The number is convenient because it collapses three coordinates into one decision, and dangerous for the same reason, since different formulas weight lightness, chroma and hue differently.

2. Instrument and geometry

A spectrophotometer with 45/0 geometry reads like the eye and suits opaque emulsions; an integrating sphere handles texture and gloss better but averages more surface. The instrument must be calibrated on a white tile at the start of each session. Two labs using different geometry will disagree by one or two Delta E units on the same sample, which is enough to fail a batch.

3. Which Delta E formula

Delta E 1976 treats all directions equally and is generous to hue shifts. Delta E 1994 and Delta E 2000 compress differences in saturated colours and weight hue more heavily. A tolerance of 2.0 under the 1976 formula is not the same as 2.0 under 2000, so the formula must be written into the specification, not assumed.

4. Tolerances that hold up

For tinted emulsions, a limit of 1.5 to 2.0 Delta E is common practice, with 1.0 used for matching within a single batch. Powders and pressed products usually need a tighter number because pigment concentration makes shifts more visible. Loose powders and products with pearlescence are harder to measure and often need a visual panel alongside the instrument.

5. Preparing the drawdown

Colour is only comparable when the film is comparable. Use the same substrate, the same wet film thickness, typically 50 to 100 micrometres, and the same drying time before reading. A wet sample reads darker than a dry one, and a thick film hides the substrate while a thin film shows it. Three drawdowns, averaged, is a reasonable minimum.

6. Standard versus batch

Keep a physical retained standard, sealed, dark and at room temperature, and replace it before it yellows, usually within a year. Reading a new batch against an aged standard slowly drags the whole production darker. Record the standard’s own Delta E against the master each time it is replaced, so the drift is visible rather than assumed.

7. Metamerism

Two samples can match under daylight and separate under warm shop lighting, because their pigment spectra differ even when the tristimulus values agree. Check every approval under at least two sources, typically daylight and a warm incandescent or LED equivalent. A pair that fails under the second source will generate returns from retail floors it never met in the lab.

8. Pigment load and opacity

At low pigment load, a tinted emulsion is partly transparent and the colour depends on what is behind it. Increasing titanium dioxide raises hiding and makes the reading more stable, at the cost of a chalkier look. When a formula changes opacity, the shade tolerance should be re-agreed, because the previous number was measured on a different optical system.

9. A workflow that repeats

Calibrate, read the standard three times, read the batch three times, and report the mean and range for each. Store the readings with the batch number. Where the instrument says pass and the eye says fail, keep the sample and escalate, because texture, gloss and sparkle all affect perception in ways a flat measurement cannot capture.

10. Where it fits

Shade control matters most in colour cosmetics and tinted care. Compare creams and brightening lotion, or read the encyclopedia on pigment dispersion.