An International Round Trial Comparing Certified Tile Calibrations to Standard Wool Top Calibrati
Abstract
The results of an international round trial comparing colour calibration media are reported. It is shown that colour measuring instruments can be successfully calibrated using a Certified Tile calibration and Illuminant D65 with the 10° Observer. While the precision of yellowness (Y-Z) is unchanged, a slight increase is experienced in the precision limits of X, Y and Z.
During the late 1970’s, the Wool Research Organisation of New Zealand (WRONZ) developed a Reference Wool to calibrate instruments used in measuring wool colour. This was done in response to unacceptable variation between colour measuring instruments and resulted in better agreement between such instruments1. However, such a calibration material does not measure colour in CIE units. CIE (Commission Internationale de l’Eclairge) is the organisation responsible for colour measurement standards. Furthermore, it has disadvantages such as being subject to soiling, and photobleaching by fluorescent light. While the calibration based on Reference Wool is transferred to a ceramic tile, the Reference Wool itself can only be used once. Thus, it would be desirable to have a more durable, certified, traceable calibration standard available to calibrate colour measuring instruments.
Recent work demonstrated that a Certified Tile calibration can produce results that are linearly related to a Standard Wool calibration when samples of top are measured. All laboratories that participated in the trial had their instruments calibrated with the same set of certified tiles. This report describes a trial designed todetermine if calibrating each instrument with a different set of tiles would also produce acceptable results.
Another feature of this trial was to calibrate and measure using Illuminant C and the 2° Observer (C/2°) on the Standard Wool calibration, while using Illuminant D65 and the 10° Observer (D65/10°) for the Certified Tile calibration. Most other industries involved in colour measurement (such as the dyeing industry) use the
latter colour space. Therefore, it is appropriate for the wool industry to use the same system.
Changing to a Certified Tile calibration will cause a shift in several units for the certified results. Furthermore, D65/10° produces slightly different results to C/2° for any given calibration. Hence, they should be incorporated at the same time to minimise disruption to the industry. A bareme between the Wool-C/2° calibration arrangement and the Tile-D65/10° arrangement is also established. This will assist in understanding the transition from the old to the new system. It should be noted that the bareme is indicative of what one would expect, but is not necessarily appropriate for each individual situation. However, it is still the best guide available for such comparisons.
Citation
"An International Round Trial Comparing Certified Tile Calibrations to Standard Wool Top Calibrations",
G.R. Shepherd, T.J. Mahar & J.W. Marler, Report 08, Raw Wool Group, IWTO, Nice Meeting, December 1998.