LimsPulse
Colorimeter · Calibration procedure

White and black tile calibration

Sets the 0% and 100% points of the reflectance scale with a black trap or tile and a certified white tile, then verifies accuracy with the white tile and a coloured check tile.

Photo of a Colorimeter
Photo: Sonal Shinde, CC BY-SA 4.0 (cropped), via Wikimedia Commons
PURPOSE

Why this is checked

All colour values are calculated from reflectance relative to the black and white references. If the white tile is dirty or the wrong values are loaded, every L*a*b* result shifts. Calibrating each session and checking with known tiles keeps the scale correct.

Frequency

Black and white calibration at the start of each session (and as often as the manual requires, often every few hours); check-tile verification daily; recertification of tiles and instrument service typically every 12 months.

Learn how the Colorimeter works
YOU WILL NEED

Standards & tools

  • White calibration tile (ceramic or opal glass) with certified reflectance or XYZ / L*a*b* values matched to the instrument
  • Black trap or black glass tile for zero
  • Coloured check tile (for example green) with assigned L*a*b* values
BEFORE YOU START

Prerequisites

  • Instrument warmed up as the manual specifies
  • Tiles clean and within certification
  • Method settings selected (geometry, aperture, D65/10°, SCI or SCE)
PROCEDURE

Step by step

  1. 1Place the black trap or black tile at the port and run the zero calibration.
  2. 2Clean the white tile, place it at the port and run the white calibration.
  3. 3Measure the white tile again as a sample and compare L*a*b* with its certified values.
  4. 4Measure the black tile as a sample and record L*.
  5. 5Measure the green check tile and compare with its assigned values.
  6. 6Calculate ΔE*ab for each tile and record the results.
RECORD

Example observation table

TileCertified L* / a* / b*Measured L* / a* / b*ΔL* / Δa* / Δb*ΔE*ab
White95.12 / −0.85 / 2.1095.20 / −0.82 / 2.18+0.08 / +0.03 / +0.080.12
Black0.40 / 0.10 / −0.200.45 / 0.08 / −0.15+0.05 / −0.02 / +0.050.07
Green check53.25 / −35.10 / 10.0553.40 / −35.32 / 10.21+0.15 / −0.22 / +0.160.31
CALCULATION

How to calculate the result

Formula
ΔE*ab = √(ΔL*² + Δa*² + Δb*²), where ΔL* = L*measured − L*certified (and the same for a*, b*)
Worked example
  1. 1

    White tile: ΔL* = 95.20 − 95.12 = +0.08; Δa* = −0.82 − (−0.85) = +0.03; Δb* = 2.18 − 2.10 = +0.08

  2. 2
    ΔE*ab = √(0.08² + 0.03² + 0.08²) = √(0.0064 + 0.0009 + 0.0064) = √0.0137 = 0.12
  3. 3
    Green check tile: ΔE*ab = √(0.15² + 0.22² + 0.16²) = 0.31
ACCEPTANCE CRITERIA

Pass if

  • White tile re-measured as a sample: typically ΔE*ab ≤ about 0.15–0.3, or as the maker specifies
  • Coloured check tile: typically ΔE*ab ≤ about 0.5, or the limit in your SOP
  • Repeatability on the white tile typically ΔE*ab ≤ about 0.05 for benchtop spectrophotometers
IF IT FAILS

What to do

  • Clean the tiles and port, check tile serial numbers and repeat the calibration.
  • Allow longer warm-up and repeat.
  • If it still fails, do not report colour results; arrange service and tile recertification.
  • Review colour results since the last good verification.
In LimsPulse · Calibration Management

LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.

See how