5.2 Reference standards for calibration of the instrument and the working standards
5.2.1 Use reference standards sufficiently frequently to ensure satisfactory calibration and
UV adjustment.
NOTE This frequency interval can be fixed according to a defined schedule or control limits (e.g. from drift analysis of
the measuring instrument).
5.2.2 Non-fluorescent reference standard for photometric calibration, issued by an ISO/TC 6 authorized
laboratory in accordance with the provisions of ISO 2469.
5.2.3 Fluorescent reference standard for use in adjusting the UV content of the radiation incident upon
the sample, having an ISO-brightness value assigned by an ISO/TC 6 authorized laboratory as prescribed in
Annex B.
5.3 Working standards
5.3.1 Two plates of flat opal glass, ceramic or other suitable non-fluorescent material, cleaned and
calibrated as described in ISO 2469.
NOTE In some instruments, the function of the primary working standard may be taken over by a built-in internal
standard.
5.3.2 Stable plastic or other tablet, incorporating a fluorescent whitening agent.
5.3.3 Black cavity, having a reflectance factor which does not differ from its nominal value by more than
0,2 %, at all wavelengths. The black cavity should be stored upside down in a dust-free environment or with a
protective cover.
NOTE The condition of the black cavity can be checked by reference to the instrument maker.
6 Sampling and conditioning
If the tests are being made to evaluate a lot of paper or board, the sample shall be selected in accordance
with ISO 186. If a lot of pulps is to be evaluated, the sample shall be selected in accordance with ISO 7213. If
the tests are made on another type of sample, make sure that the test pieces taken are representative of the
sample received.
Conditioning according to ISO 187 is recommended but not required, but preconditioning with elevated
temperatures should not be applied since it might change the optical properties.
7 Preparation of test pieces
Regarding pulp samples, prepare laboratory sheets in accordance with ISO 3688.
Avoiding watermarks, dirt and obvious defects, cut rectangular test pieces approximately 75 mm × 150 mm.
Assemble at least ten of the test pieces in a pad with their top sides uppermost; the number should be such
that doubling the number of test pieces does not alter the radiance factor. Protect the pad by placing an
additional sheet on both the top and bottom of the pad; avoid contamination and unnecessary exposure to
light or heat.
Mark the top test piece in one corner to identify the sample and its top side.
If the top side can be distinguished from the wire side, it shall be uppermost; if not, as may be the case for
papers manufactured on double wire machines, ensure that the same side of the sheet is uppermost.