Measuring Reflectance on the 577 for Powder Samples
2. Prepare an homogeneous sample in any way which has been have found useful for other measurements you currently use. Small beads have been used without crushing. Try to have a sample that covers the bottom of the cuvet with as little air space as possible. Experiment a little to see how necessary this is for your application.
3. Fill the cuvet about 2/3 full and tap gently to settle the powder. Use the PRESS (Part 3690101) to firmly press the sample into place or manually compress the powder. Observe the bottom of the cuvet and ensure that there are no air spaces, etc. Wipe off the bottom of the cuvet so that there is no powder on it. This is the extent of sample preparation prior to measurement.
4. Polish the optical disc (Part 2657009) and remove any dust particles. Place this on top of the opening of the search unit and cover with the black cavity standard (Part 2657012).
5. Remove the black cavity standard and replace it with the standard plaque on top of the search unit-with the optical disc between the light beam and the plaque. This gives the same physical configuration for the standard as when you place your filled cuvet on the light opening of the search unit. Standardize the plaque.
6. Remove the standard plaque and the optical disc and place the filled cuvet on the search unit. Cover the cuvet with the black cavity standard.
7. Obtain reflectance values in the approved manner.
8. If you are using the PHOTOVOLT computer program for CIE color coordinates, obtain reflectance values for the AMBER, BLUE and GREEN filters. Always have the optical disc in place for standardization but remove when you are using the filled cuvets.
9. If you are determining WHITENESS according to ASTM 313, (using the equation for whiteness, WI = 4 B – 3 G), the value is easily hand calculated. L*a*b* and other color co-ordinates require more elaborate calculations but are easily done with the PHOTOVOLT computer program.