Petrov (neTpoB) and MefaMe (MefaMe) designed a special instrument in order to measure the darkening degree of Guanbei white under the action of light. This instrument is also suitable for determining the degree of darkening of other pigments. A sketch of the instrument is shown in Figure 37.
The principle of the instrument is as follows: the light from the electric lamp 1 is irradiated on the pigment sample 2 placed in the groove of the special receiver 3, when the light is reflected from the surface of the pigment, it is collected by the lens on the surface of the photoelectric tube 4 superior. The magnitude of the photocurrent excited by the light is recorded by the galvanometer 5 . (Related instrument: Colorimeter)
The method for measuring the degree of darkening of lithopone is as follows. Put water and slurry-like zinc whitening in the drawing tank of the receiver 3 and cover it with a quartz plate before being irradiated by ultraviolet light. After placing the susceptor in the instrument, measure the photocurrent excited by the light reflected by the second barium white. After the first measurement, irradiate the paste-like zinc-coated white mercury quartz lamp or arc lamp in the receiver, and after a certain period of time (10 minutes of gold), put the receiver back into the receiver, and Make a second photocurrent measurement. Connect to the galvanometer and record the difference of the photocurrent value to judge the degree of darkening of the bright silvery white.
