CHEMICAL WORLD THIS WEEK
HESEAH€H PROGRESS Color chemists c a n obtain standards f r o m NBS on 10 of t h e m o s t i m p o r t a n t commercial standards for accurate color measurement of c h r o m a t i c specimens
c;
•IHOMATIC
reflectance
standards
for
photoelectric reflectometors in the tri stimulus colorimetry of reflecting speci mens are now available from the National Bureau of Standards. These standards are intended for use with instruments designed to measure 45°0° directional reflectance, and which are equipped with photocells, light source, and tristimulus filters. The latter must have spectral specifications approximating the tristimulus values of the standard observer and coordinate systems of the International Commission on Illumination. The standards cover 10 important com mercial colors. Since the spectral response functions for the source-filter-photocell combina tions generally do not duplicate exactly the corresponding functions obtained by combining ICI tristimulus values and illuminant C, the differences may cause error in color measurement. However, if the difference in spectral selectivity be tween specimen and standard is small, the error in color measurement will also be small. The standards therefore will per mit much more accurate color measure ment of certain chromatic specimens than has been possible with the neutral (white, gray, black) series of standards available since 1945. Each set consists of 10 3- by 5-inch porcelain-enameled iron panels having the colors, etched designations, and nomi nal values of reflectance and chroma-
ticity given in Table I. The standards are measured for 45° 0 s' directional re flectance on a multipurpose reflectometer equipped with tristimulus filters. Instru-
Table I. Colors, Designations, Reflectances, an d Chromaticity Coordinates of Standards* Chromaticity Coordinates Reflectanc '/ι Ktched Y Amber "" X Designation Blur" Green 73 0.311 0.320 73 72 SKC-SHC-OO 24 22 31 0.290 0.384 SBC-12 29 22 34 0.315 0.389 SKC-15 36 36 32 0.324 0.289 SBC-20 62 31 57 0.373 0.383 SKC-SBC-U 61 21 54 0.405 0.410 SBC-35 20 37 24 0.254 0.263 SBC-40 12 37 16 0.209 0.215 SKC-41 3.6 18 4.3 0.185 0.145 SKC-SBC-45 19 1.0 7.3 Red 0.632 0.317 SKC-70 " The standards may be ordered from the National Bureau of Standards, Washington 2 5 . E>. C . for $75 per set. Color White Bath jin-fii Kitchen ^rcea Orchid Ivory Maize Bath b l u r Delphinium blue Royal b l u r
mental calibration errors are eliminated by comparing the panels directly with the NBS reference standards. Values of the directional reflectance are obtained in per cent relative to magnesium oxide as 100% for the blue, green, and amber tristimulus filters. The values for the green filter are the luminous directional reflectances for ICI illuminant C. The uncertainty in the reported values of directional reflectance varies approxi mately from 1% of the value for high reflectances to 107r of the value for low reflectances. Experience with porcelainenameled iron reflectance standards indi-
Set of standards being used with multipurpose photoelectric reflectometer
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cates that they are reasonably permanent if used carefully to avoid abrasion. Panels that have been stored for a year or so develop what appears to be "bloom" (especially noticeable on dark-colored panels), but this can be removed by wash ing with soap and water. The following recommendations are made for the use of the reflectance stand ards : ( 1 ) Before use, always wash stand ards with soap and warm water, rinse and dry with a clean towel. (2) Handle carefully to avoid abrading the surfaces.
CHEMICAL
One or two deep scratches are not as serious as a large number of small, almost imperceptible ones. (3) Do not attempt to do accurate tristimulus colorimetry of materials having spectral selectivity very much different from the standards. Shale-Oil W a x Research R e p o r t e d b y Mines Bureau Future market demands for paraffin waxes made from petroleum can be partly met b y waxes processed from oil shale mined from large reserves in Colorado, Wyoming, and Utah, according to a Bureau of Mines report. Fully refined shale-oil wax is virtually identical with the fully refined petroleum variety and could be used in the manu facture of food containers, the report states. The cost of making the crude and semirefined grades would be about the same as in making petroleum paraffin wax, while the cost of making a fully re fined shale-oil wax would be somewhat greater than for fully refined petroleum paraffin, the publication estimates. Bureau technologists at the Laramie, Wyo., Petroleum and Oil-Shale Experi ment Station and the oil-shale demonstra tion plant at Rifle, Colo., collaborated in producing waxes from shale-oil distillates. The report describes methods used in extracting, refining, analyzing, and test ing, and lists the physical properties of the waxes. It also includes comparative tables, charts, and illustrations of appara tus. A free copy of Report of Investigations 4708, "Waxes from Shale-Oil Wax Dis tillate/' may be obtained by writing to the Bureau of Mines, Publications Distri bution Section, 4800 Forbes St., Pitts burgh 13, Pa. AND ENGINEERING
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