With the purpose of elucidating the cause of cracks and deterioration in the final paint film of an.overlapped oil painting, a relation between changes with time in paint film and the overlapped paint film has been investigated by coating an oil paint composed primarily of white lead, zinc white, and titanium white on a canvas and then analyzing products formed in the paint film during a period of time. As a result, the following new facts were observed : 1. With regard to a known knowledge that lead white and zinc white as active pigments react with vehicle to form metal soaps, the experimental results could not afford a persuasive explanation for their quantitative relations. However, it was observed that they were different as to the amounts of metal soaps formed. 2. As for the zinc white paint film, it was inferred that zinc soap was remarkably formed and the formation of the zinc soap was the major cause of cracks in the final paint film. 3. In contrast with a well-known knowledge that pigments tending to react with vehicle to form metal soaps are less chalked, the experiments conducted this time revealed that chalking was accelerated as metal soaps were formed, but that no formation of metal soap was observed and also no chalking was recognized for the paint film of titanium white as an inert pigment.
Contact charging was measured against reference Fe powder. A blow-off apparatus which is recently developed having a unique Faraday cage structure was used for the measurement. As the amount of aminosilane adsorbed on silica powders was increased, following were observed. (1) the contact charge varied from (-) to (+) value. (2) the pH value of these powders dispersed in deionized water became larger. (3) the zeta potential varied from (-) to (+) linearly as the contact charge varied toward (+) direction. From the above facts it is obvious that the contact charging is in close correlation with the acidity (or basicity) of the powder surfaces, the decrease in the acidity being due to the replacement of the silanol groups of the silica surface (which act as H+ ion doners) by the amino groups of the silane (which act as H+ ion accepters). These facts also suggest a general possibility that the contact charging of a fine powder can be controlled by suitable selection of both the species and number of the functional group (e. g. -NH2) adsorbed on its surface.