Accurate matching of colors is becoming increasingly important to modern industry.
Household appliances such as stoves, refrigerators, washing machines, and clothes dryers may be assembled from parts produced on different production lines and finished with different materials. A noticeable color difference between parts may be objectionable to the customer and may hurt the sale of the product.
Likewise, for many other uses, such as advertising signs, trade marks, traffic lights, and railroad signals, color is rigidly specified and closely controlled.
For many years manufacturers and purchasers of colored materials have employed inspectors to determine whether or not two samples are sufficiently similar in color to be called a "match."
Frequently inspectors cannot agree, and in recent decades instruments have been developed to measure color and color differences precisely.
But the extent to which instrumental values of color differences agree with estimates of human observers is a question that has never been satisfactorily resolved.
To obtain data which may lead to a solution of this problem, the National Bureau of Standards, in cooperation with the Porcelain Enamel Institute, embarked some years ago on a long-range research program. Although much experimental work remains to be done, preliminary phases of the investigation have provided significant information on the evaluation of color differences.
This initial stage of the program has been carried out by J. C. Richmond, H. J. Keegan, and H. K. Hammond of the NBS staff and R. S. Hunter, Director of Hunter-lab, with the cooperation of a number of industrial laboratories.
For estimation of color differences, approximately 200 porcelain enamel specimens were prepared in 1.5 groups of 13 panels each. Each group contained one panel which represented the "standard" color. The other panels of the group represented departures of approximately one and two steps in each of the six directions : lighter, darker, stronger, weaker, and toward the two adjacent hues. Thirty-four observers from 10 cooperating laboratories were then asked to estimate visually the relative magnitude and most prominent directions of the color differences between each specimen and the corresponding standard for that group.
Nineteen of the 34 observers were classed as experienced in color matching while 1.5 were without experience in color work.
The data from the two groups of observers were averaged separately 4'4