ALTANA Pfund Cryptometer - Manual (Page 3)

Description
DIRECTIONS FOR DETERMINING WET HIDING POWER BY THE USE OF
THE PFUND CRYPTOMETER
General Remarks: All parts of the instrument – in
particular the clear top plates – must be kept
perfectly clean.
Caution: Do not use solvents to clean the base
plate
While sky-light may be used for illumination in
some cases, artificial light – a 100 watt or a 200
watt bulb – has been found to yield the most
reproducible results. Strong illumination should
strike the Cryptometer from the scale side at an
angle of 45°. Allow as little light as possible to
strike the eyes. For best results, conduct all tests
at temperatures between 70° and 80° F.
For a right-handed operator, the Cryptometer
should always be assembled and operated so
that the scale to be read is on the left, the pegs of
the tilted top plate are on the right, and the light
strikes the thin side of the wedge-shaped film from
the left.
A small amount of thin lubricant, applied to the
outer surfaces of base plate only, where it is
touched by the moving top plate, will prevent
scratches that impair the accuracy of the
instrument.
Stir the paint sample thoroughly so that all
pigments are uniformly distributed. Be careful to
avoid air bubbles. Apply a small pool of paint to
the center of the base plate. If too much paint is
used, there will be an overflow into the longitudinal
Description
grooves and finally over the outer strips, which at
all times must be kept free of paint.
Select the top plate with the most appropriate
wedge constant and place it with the pegs down
on the side opposite the illuminated scale. The
number (2, 3, 5 or 7) assigned to a top plate
indicates the increasing slope of the underlying
paint film. It also corresponds to the actual film
thickness, in mils, when the touching edge is
set to read 25.4 mm = 1 inch = 1,000 mils on
the engraved scale. This check point should be
marked very near the center of the 0-50 mm
scale where the best precision can be obtained.
It should be used to form a wet film of known
thickness for selecting the proper top plate and
moving it in the proper directions.
To make a reading, press lightly but evenly on the
four corners of the top plate, move it back and
forth several times to force out all surplus paint,
and then move it slowly to the left until the center
line of demarcation has disappeared completely
over its entire length because of increased wet
film thickness. Record the scale reading, located
directly under the lower left-hand corner of the
top plate, and call it “disappearance.” After
moving the top plate about 5 mm. further to
the left, reverse the motion while still pressing
down on the four corners as before. Move the
top plate to the right slowly until the center line
of demarcation reappears over its entire length
because of decreased wet film thickness. Record
the reading as before, and call it “appearance.”
The average of 5 such pairs of readings will
provide a practical mean for the Cryptometer
setting corresponding to visual hiding. Rest the
eyes by looking at a dull black surface (such as
black felt) or by closing them for a minute, and
Description
3 2