January 15, 1930
I S D C S T R I A L A N D ENGlNEERlNG CHEMISTRY Literature Cited
(1) Bonney, U. S., (2) Gardner, (3) Gregory,
Drugs, Oils Points, 88, 386 (1923); Paint hffrs. Assocn Tech. Circ. 198. Paint Mfrs. Assocn. U. S., Tech. Civc. 265. Rassweiler, a n d Lampert, J . Rheology, 1, 30 (1929).
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(4) Notiy, d u , J . Gcn. Physiol., 1, 521 (1919); Central Scientific Co., Auli. 82. ( 5 ) Williamson, Patterson, and H u n t , IND. END.CHRM.,Si, 1111 (1929); also paper presented before Division of Paint and Varnish Chemistry a t 77th Meeting of American Chemical Society, Columbus, Ohio, April 29 t o M a y 3, 1929,
Evaluation of the Contrast-Obliterating and Brightening Power of White Pigments‘ George S. Haslam TEE S E W JERSEY ZINC C D l a P A N Y : P A L M E R T O N . PA.
r\: COKSIDERIKG the % . m e t h o d for t h e evaluation of brightening power a n d contrast-obliterating power has been presented. The choice of a pigment in formulating a paint, the d a t a obtained, using six of t h e more c o m m o n white nature of the task to be pigments, a r e presented a n d the increase i n hiding power w i t h decrease i n brightness is shown. accomplished must be conT h e d a t a indicate that t h e value at which the eye is sidered. If i t i s d e s i r e d capable of detecting c o n t r a s t is less than the generally to obliterate a contrast between a high and low accepted 98 Per cent. brightness regardless of the resulting brightness, then a pigment of one type may be selected, but if it is desired to bring a dark background to the highest possible degree of whiteness or brightness, then an entirely different pigment may be used. It is assumed that in most cases it is desired to eliminate any contrast that may exist and a t the same time impart to the surface the greatest brightness possible. Therefore, in order to evaluate a white pigment it is necessary to express the con-
CONTRAST RATIO-If a contrast exists on the surface to ~ ~ a ~ “contrast which will be the brightness of the black divided by the brightness of the white* CONTRAST OBLITERATING PoWR-The “contrast-oblit-
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tionship betneen hid’O0 u/nlmo+. ar .-* ing poi\ er and tinting strength has been pro?
