CHAPTER IV
PHYSICAL LABORATORY PAINT TESTS
For the paint chemist who desires to familiarize himself with the more recent analytical methods worked out in American laboratories, reference may be had to treatises on the analysis of paints, by Gardner and Schaeffer,[13] and Holley and Ladd.[14] Analytical methods are not included in this chapter, the writer’s desire being to treat the subject from the standpoint of the physical properties of painting materials. The work outlined herein is of a nature that affords a wide field of research, and a brief study will doubtless suggest similar work to the student of paint.
[13] The Analysis of Paints and Painting Materials. McGraw-Hill Book Co., New York, 1910.
[14] Mixed Paints, Color Pigments and Varnishes. John Wiley & Sons, New York, 1908.
Preparation of Paint Films. The study of paint films is one that has become of vital importance, and is receiving at the present time great attention. Among the many methods which have been suggested and attempted for securing paint films, a few already well known may be mentioned.
By painting upon zinc and eating away the zinc with acid: The objection to this method is very evident, namely, the action of the acid upon the paint coating, which is likely to be very severe. Another method has been to spread paraffin on a glass plate, and painting upon this surface. When the paint is dried, the paraffin is melted off and thus the film is obtained. This method is open to objections, in that the paraffin surface is not a comparable one upon which to paint, and also that the complete removal of the paraffin is not assured.
Another method consists in covering a piece of glass with tin foil, painting out the film upon the foil, and after drying properly, to remove the sheet of foil with its coating of paint and immerse in a bath of mercury which, by amalgamation of the tin, leaves the paint film.
We now come to a method worked out in our laboratories, which can be recommended as being not only simple but efficient and practical. It has been found that a size from noodle glue, when painted upon ordinary fair-quality paper, makes a surface from which the paint may be subsequently stripped. The paint is applied in the ordinary way to the paper, which is held during the operation by thumb tacks, and allowed to dry. The paint may be separated by immersion in water kept at about 50 degrees Centigrade. By this method large films may be obtained, but it has been found very unhandy to work with films exceeding an area of eight inches square. When the film of paint has been detached from the sized paper through the dissolving of the noodle glue, the paint film is then immersed in a fresh solution of water, in order to remove whatever excess of noodle glue there may be remaining. A glass rod is then introduced into the bath, in which the paint film is floated upon the glass rod, which is then hung up to dry in a suitable container to prevent the accumulation of dust, etc.
