• Manufacturing control and testing
• Cost reduction through close control of coating thickness
• Testing incoming shipment for conformity with wet hiding power specification

The cryptometer operates by forming a wedge-shaped film of paint between two optically ground and finished glass plates - a graduated opaque base plate and a transparent top plate. The plates are separated at a fixed angle. When the top plate is moved back and forth, a line of demarcation on the base plate alternately appears and disappears when the paint film is of sufficient thickness to produce complete hiding of the base plate. The graduation in mm at that point of the base plate is converted to hiding power sq. ft./gal.) and thickness (mils) by an accompanying chart. Chart calculations are based upon the tangent of the angle separating the plates and the length of the paint film in mm at the point where complete hiding is produced.

The Black and White Cryptometer tests paints and pigments of all colors, including all of the chromatic colors and the blacks, whites and grays. The base plate of this model has two graduated sections of opaque glass - a black section for testing of paints or pigments having a reflection factor of greater than 70%, and a white section for darker paints and pigments. Two top plates are furnished - one having a wedge constant of .007 for paints of lesser opacity and one with a .002 wedge constant for paints of greater opacity.

All parts of the instrument – in particular the clear top plates – must be kept perfectly clean.
Caution: Do not immerse in solvents.

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 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 25.4mm = 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 5mm 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 then confirm visual hiding of the paint sample at the average setting.

1. Follow carefully the instructions given under “General Use”
   
2. Place the Cryptometer so that the black field is to the left, apply a small pool of paint at the dividing line between the black and white fields, lay the top plate on it so that the pegs are to the right, and make 5 pairs of readings for “disappearance” and “appearance”.
   
3. Reverse the Cryptometer so that the white field is to the left, and proceed as before to make 5 pairs of readings.
   
4. Average the 5 quadruple sets of readings – disappearance and appearance over both black and white fields – to obtain a practical mean setting that can be confirmed for visual hiding after resting the eyes.
   
5. Refer to Table I, under the column heading for the top plate used, to obtain the corresponding Wet Hiding Power in square feet per gallon and also the corresponding Wet Film Thickness in mils or thousandths of an inch.

1. Weigh out an appropriate volume of the pigment and place it on a glass rubout plate.
   
2. Measure out an appropriate volume of refined linseed oil and add it to the pigment.
   
3. Make a homogeneous mixture of the pigment and oil, using a glass muller and spatula, so as to attain the appropriate painting consistency in this pigment-in-oil dispersion.
   
4. Apply a small pool of this dispersion to the lower plate of the most appropriate model, select the top plate with the most appropriate wedge constant, and proceed to determine an average Cryptometer setting as described above.
   
5. Compute the wet hiding power of the pigment according to the formula:

• X = wet hiding power in terms of units of area per unit weight of dry pigment;
• V = total volume equal to the sum of the pigment volume and the oil volume;
• K = top plate wedge constant or slope;
• L = Cryptometer setting, and
• M = weight or pigment only.