Page:Colorimetry104nime.djvu/43

Fig. 27.Chromaticities of some standards for grading petroleum products (solid circles), rosin (crosses), and honey (squares).The solid curve is generated by an ideal absorption-band sweeping across the spectrum from the short-wave to the long-wave band [40]. The standards have broad absorption bands of different sharpness. with a shift in the wide absorption band toward the ultraviolet as brown pigments are removed on refining. The differences in scales among these products correspond to differences in sharpness of the absorption band, with oils possessing the sharpest bands, rosins next, and sugars least sharp. Figure 27 compares, on the 1960 CIE-UCS [80] chromaticity diagram, the chromaticity locus generated by varying an ideal absorption band (40) with a few color standards used for petroleum solid dots), rosin (crosses), and sugar (squares) products.

It is sometimes convenient to state the color of a product in terms of its equivalent on another scale and modified by an adjective that describes the off-locus position. Thus U. S. Rosin Standard X (extra water white), which is equivalent to ASTM petroleum color 1.4 but slightly on the purple side, will be designated 1.4p. The letter g will be used to designate departures toward green.

Table 12. Chronmticity coordinates of Planckian radiators ($c_{2}$ = 14,380) and standard sources

Source (°K)	2° Observer system				10° Observer system
	$x_{2}$	$y_{2}$	$u_{2}$	$v_{2}$	$x_{10}$	$y_{10}$	$u_{10}$	$v_{10}$
1000	0.6526	0.3447	0.4482	0.3547	0.6474	0.3504	0.4383	0.3555
2000	.5266	.4133	.3050	.3590	.5300	.4122	.3078	.3591
3000	.4368	.4041	.2506	.3476	.4403	.4026	.2532	.3476
4000	.3804	.3767	.2251	.3344	.3827	.3759	.2266	.3345
5000	.3450	.3516	.2115	.3231	.3464	.3515	.2119	.3234
6000	.3220	.3317	.2034	.3141	.3227	.3323	.2030	.3146
7000	.3063	.3165	.1982	.3070	.3066	.3176	.1973	.3078
8000	.2952	.3048	.1947	.3014	.2951	.3063	.1934	.3022
9000	.2869	.2956	.2970	.1920	.2866	.9975	.1905	.2979
10000	.2806	.2883	.1904	.2933	.2802	.2905	.1884	.2944
∞	.2399	.2342	.1800	.2636	.2394	.2366	.1786	.2648
A	.4476	.4075	.2560	.3495	.4512	.4059	.2588	.3496
B	.3485	.3517	.2137	.3235	.3498	.3527	.2138	.3241
C	.3101	.3163	.2009	.3073	.3104	.3191	.1994	.3086
E	.3333	.3333	.2105	.3158	.3333	.3333	.2105	.3158

a. Petroleum Products

For more than 30 years the color of lubricating oils and petrolatum has been graded by comparison with the colors of 12 glass standards [7]. The petroleum product in a 33-mm layer and the standard are illuminated by artificial daylight produced by combining an incandescent lamp of color temperature approximately 2750 °K with a filter of Corning Daylite glass specially selected to have spectral transmittances within specified tolerances and further to have for standard source A luminous transmittance, $\phi _{v}$, and chromaticity coordinates, within the limits:

$\tau _{v}$	0.107 to 0.160
$x$	.314 to  .330
$y$	.337 to  .341
$z$	.349 to  .329

The specimen holder, the magazine containing the glass color standards, the artificial daylight assembly, and a viewing diaphragm defining the direction of view are mounted together to form a portable instrument known as the Union colorimeter.

Table 13 gives the Lovibond analysis of the glass color standards (6), the luminous transmittance, $\tau _{v}$, and chromaticity cordinates, for source C [141], the color names used by the International Petroleum Association, and the nearest chromaticity match on the new ASTM color scale, which was adopted in 1957. This new scale consists of a set of glasses which define a scale that is closer to the range of petroleum colors and with improved step uniformity [48, 72].

Table 14 gives for these glasses the luminous transmittances and chromaticity coordinates for source C in the defining UCS (r,g-system as well as in the standard CIE ($x,y$)-system. Also listed re the luminous transmittance tolerances for the glass standards and their equivalents on three other scales.

The grading of naphthas, kerosines, and so on, has for many years been carried out by comparison of the color of rather thick layers (up to 20 in) of the refined oil with the colors of a set of three color standards made of yellowish glass. The Saybolt