The white standard WS DIN 5033 is a barium sulphate tablet produced
with the powder press. This standard is mainly used as a primary
standard for the calibration of working standards for reflectance
photometers but it can also be used as a working standard itself.
The white standard must have a very even, flat, clean and mat surface;
the values of the spectral reflection factor must be known. The
even surface is achieved by pressing the barium sulphate powder
in the press against a matted glass which is later removed.
Within one batch, the spectral reflection factor's reproducibility
is ± 0.1% and therefore better than the ± 0.2% required by DIN 5033,
standards with a nominal diameter of 40 mm can be produced using
the powder press 40 described here. The nominal diameter of the
white standard should always be larger than the measuring port of
the instrument to prevent false measuring results caused by the
The barium sulphate powder is pressed into a metal ring which is
closed with a plate at the back after pressing. In this way, the
tablet is entirely surrounded by a metal mount. The tablet surface
is flush with the front surface of the holder; this permits exactly
defined positioning of the white standard against the measuring
port of the photometer. If produced correctly, the tablet is so
compact that it will not lose any powder even when positioned vertically
or with its surface pointing downwards.