ASTM D6045 Color of Petroleum Products by the Automatic Tristimulus Method
6. Apparatus
6.1 Either instrument described in 6.1.1 or 6.1.2 may be used in this test method.
6.1.1 Spectrophotometer - The spectrophotometer used in the measurement shall satisfy the following specifications:
6.1.1.1 Wavelength Range - 380-780 nm.
6.1.1.2 Effective Wavelength Width - The effective wavelength width of the radiant flux from the slit of the spectrophotometer shall be 10 +/- 2 nm or 5 +/- 1 nm.
6.1.1.3 Linearity - +/-0.5 % of full scale. Photometric reproducibility - +/-0.2 %.
6.1.1.4 Wavelength Accuracy - +/-1 nm.
6.1.1.5 Geometrical Conditions - Normal illumination and collection. The illumination light flux shall not include a ray which has an angle of five or more degrees toward the central line. The angle of the center line inclination of the illumination flux shall be 0 +/- 2°toward the normal line of the sample surface.
6.1.1.6 The spectrophotometer shall have the capability to compute tristimulus values (CIE XYZ) using CIE Standard Illuminant C and the CIE 1931 Standard Observer.
6.1.1.7 A spectrophotometer that gives results comparable to those of the instrument described in 6.1.1.1-6.1.1.6 shall be satisfactory.
6.1.2 Tristimulus Filter Colorimeter - Instrument designed for high precision color measurement of clear liquids. The instrument shall be capable of converting the light transmitted by a sample (under normal illumination/normal detection) into tristimulus values (CIE XYZ) using the CIE Standard Illuminant C and the CIE 1931 Standard Observer using Practice E 308. A correlation between measured tristimulus values and Test Method D 1500 and Test Method D 156 numbers shall be used to yield an equivalent instrumental ASTM color and/or Saybolt value. The instrument shall be capable of automatically computing ASTM color or Saybolt values, or both.
6.1.3 Sample Cell - Sample cell shall be clean, clear, colorless, and unaffected by the petroleum product being measured. Cells with path lengths of 33 mm have been found suitable for measuring ASTM color, and cells with path lengths of 100 mm have been found suitable for measuring Saybolt values. The operator shall follow the instrument manufacturer's procedures and recommendations.
7. Reagents and Materials
7.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
7.2 Diluent - Kerosine (Warning - See Note 2) having a color of +21 saybolt color or lighter by this test method or Test Method D156, or 1.5 by method B of IP 17. This material is used for diluting dark samples to be measured for ASTM color.
NOTE 2 - Warning: Combustible Vapor Harmful.
8. Sampling
8.1 Samples shall be taken in accordance with Practice D4057.
9. Preparation of Sample
9.1 Liquid Petroleum Products such as Lubricating Oils - If the sample is not clear, heat it 6°C (10°F) above its cloud point (see Test Method D2500) and observe the color at that temperature. When the sample is darker than ASTM Color 8, mix 15 volumes of the sample into 85 volumes of the solvent kerosine, and test the mixture.
