56 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS perature can be applied to these only with a considerable degree of approximation. Nevertheless, it is so convenient to refer to a simple and single number that color tem- perature is commonly used even for fluorescent light. The spectral dis- tribution curve and the color tem- perature are the scientific terms used to describe the illumination which is one of the factors involved in the perception of color. ß The second factor in the percep- tion' of color is the object. The fundamental specification of the color of an opaque object is the curve in which reflectance is plotted rs. wave length. In the case of clear liquids, the curve of transmission rs. wave length is the fundamental specification of color. If we con- sider that white light containing all the different colors of the' rainbow is falling on a sample, a colored sample will selectively reflect these different kinds of light. A red sample will reflect more of the red light which is incident upon it than the blue light which is incident upon it. The white light has been altered in its spectral distribution by encounter- ing the sample. One of the easiest ways to determine the reflectance characteristics of a sample is to measure it with an automatically recording spectrophotometer. This is an instrument which consists of a monochromator and a photometer. The function of the monochromator is to furnish light of only one wave length at a time, varied through all the rainbow colors as the plot is made automatically. The function of the photometer is to compare the amount of this particular color light which is reflected from the sample to the amount which is reflected from the white standard. The white standard is usually taken to be magnesium oxide. This instrument automatically plots the reflectance curve or the transmission curve for a particular sample. This curve can be the specification of the color. Because the durve of reflectance rs. wave length for a particular sam- ple is difficult to talk about, it is common practice to reduce the data to a simpler set of numerical figures. It has been found that in general, at least three dimensions are necessary to specify a color. In this discus- sion we can do scarcely more than mention some of the more common ways of specifying the color. One of the methods is to use tri-stimulus values. As is well known by color marchers, using red, yellow and blue dyes or pigments in the proper pro- portion, it is possible to produce all dull colors. It is thus possible to express dull colors in terms of amounts of the three pigment pri- maries needed to duplicate them. In the tri-stimulus values, this fundamental method is used. A color is expressed in terms of three imaginary, additive primaries which have been internationally standard- ized by physicists and psychologists. Another way of specifying a color which also involves three terms, is to use the terms "apparent luminous reflectance, .... dominant wave len. gth," and "excitation purity." This is an additive method of speci-

COLOR MATCHING IN THE COSMETIC INDUSTRY 57 lying a color which can be demon- strated physically with real colors. If white light is mixed in with spec- tral light, and the intensity of the mixed light adjusted, any particular color may be duplicated and thereby specified. A third method of specifying color is in the Munsell notation. The Munsell notation involves specifying again three factors: value, hue and chroma. Value is related to the total amount of light reflected. Hue is related to the name of the color, that is whether it is red, green or blue. Chroma is related to in- tensity of a color, that is, it is the attribute by which a cherry red differs from a brick red. In all of these cases where color is specified in terms of three numbers, the color of the illuminant and the properties of the eye must be taken into consideration. Therefore, if two samples have the same specifi- cations in terms of any of these three simpler numbers, it means only that they will appear alike to a standard observer under standard illumination conditions. The fun- damental specification of the color attribute of a sample itself is the spectrophotometric curve. The eyes of individuals which are the third factor in appearance of color, vary quite widely in color per- ception. One reason for this is the phenomenon of color blindness. Colors which are confused by one person may be easily identified and distinguished by another person. Another factor which leads to differ- ences is the age of the observer. As the observer grows older, a yel- low pigment develops in the eye and this has the effect of giving a sample the appearance of being viewed under tungsten light. Thus an old person and a young person may look at two samples under north sky light and the younger observer may find that the two samples look alike but the older observer because of the yellow pigment in his eye is effec- tively viewing them under tungsten light where there may be mismatch and he may call the two samples different. An imaginary person with average eyesight, the so-called standard observer, has also been internationally adopted. The process of observing color is thus a complex one involving all the variations of the illuminant, the sample, and the human eye. The only way that one can be sure that two samples will look alike to all observers at all times is to have their. spectrophotometric curves identical, and even this must be qualified by the statement that they possess equal fluorescent properties and geometries. There are two methods of mixing colors to get a desired new color. One is the additive method of color mixture, and the other is the sub- tractive method of color mixture. In the additive method of color mixture, one starts out with no light at all, and adds to the amount of light which the observer can see. This method is the basis of the tri- stimulus specification, but is of lesser interest to the cosmetic color- ist because the cosmetic colorist