L*a*b*, Illuminant C, UV Adjusted

This test is performed to determine the L*a*b* colour coördinates at C/2° of paper, solid board or folding board. The light reflected from a sample under specified conditions is analysed either by a tristimulus-filter colorimeter or by an abridged spectrophotometer, and the colour coordinates are then calculated.

Operate the instrument in accordance with ISO 5631-1 and the manufacturer’s instructions.

Leave the samples exposed for 24 h to 23°C and 50% R.H., according to ISO 187.

Calibrate the instrument according to the instrument maker’s instructions, using a non-fluorescent ISO reference standard of level 3 (IR3). Adjust the UV-content to the C/2° Illuminant/observer.

Each sample pack is made of a pad of paper to be tested and a coloured cover sheet.

Remove the coloured protective sheet from the test piece pad.

Place the test piece in the position indicated on the cover sheet.

Without touching the test area use the procedure appropriate to the instrument to obtain the three CIE tristimulus values of the first test piece (or CIELAB values if the instrument is designed to report directly in this colour space).

Record the L*, a* and b* coordinates (calculated or measured).

Move the uppermost test piece to the bottom of the pad and determine the values for the next and similarly for the following test pieces until at least ten test pieces have been measured.

Report 10 measures of L*, A* and b*, their mean and standard deviation calculated to 3 significant figures.