Measuring Fibers
The instrument illustrated below is an UltraScan VIS. Measurements on an UltraScan PRO or ColorQuest XE would be carried out in a very similar fashion.
The color of fibers is often measured before the final product is produced. These fibers are typically translucent and must be measured as masses of a consistent size using special accessories and presentation techniques. Several readings of each mass should then be averaged for the final result, preferably with replacement of the sample between measurements.
A HunterLab UltraScan VIS diffuse/8° spectrophotometer with the 1.0-inch area of view can be used to measure the reflectance of fibers using the compression cell assembly. This is the most common method advocated by HunterLab for the measurement of fibers.
The UltraScan VIS
The Application
Fibers have several non-uniform characteristics that require compensating preparation and presentation techniques in order to ensure a repeatable sample measurement.
Fibers are not a flat solid sample and must be measured through the bottom of a clear glass sample cup in order to be effectively made into a solid.
Fiber masses are irregular in size and shape, requiring the averaging of several readings with replacement.
Fibers are sometimes translucent — not opaque — and will be sensitive to ambient light and to small differences in the optical configuration of the instrument. Using a sufficient and constant sample thickness (at least 5 mm) will make the measurements more repeatable.
| Recommended Color Scale | CIE L*a*b* as a full color descriptor |
| Recommended Illuminant/Observer | D65/10°. C/2° may also be used. |
Measurement Method
| 1. Configure your software to read using the desired color scale, illuminant, and observer. | |
| 2. Standardize the instrument for the large area of view in Reflectance - Specular Included mode using the light trap and calibrated white standard that comes with the instrument. |  |
| 3. Replace the regular port insert with the special port insert that is part of the compression cell assembly (HunterLab Part Number D02-1011-131 for ColorQuest XE and UltraScan VIS, L02-1012-387 for UltraScan PRO) and replace the original sample clamp with the modified sample clamp. |  |
| 4. Connect the air compressor to the assembly as described in the instrument user's manual. |  |
| 5. Weigh a fixed amount of the sample material into the sample cup. The fibers should completely fill the cup. Using a sufficient amount of sample and a constant weight of sample makes measurements more repeatable. |  |
| 6. Place the sample cup into the cup holder port plate and adjust the sample clamp to hold the cup in place. |  |
| 7. Turn on the compressed air and adjust the pressure as described in the instrument user's manual. | |
| 8. Flip the pressure switch on the sample clamp to the on position (up). The clamp will compress the sample into the sample cup. A smooth, flat surface is now available for measurement. Using a constant pressure makes measurements more repeatable. |  |
| 9. Take a single color reading of the fibers through the bottom of the sample cup. Empty, reweigh more sample, refill the cup, and remeasure it at least three times from the same batch. Average the three color readings for a single color measurement representing the color of the batch. Averaging multiple readings minimizes measurement variation associated with non-uniform samples. | |
| 10. Record the average color values for the sample batch. |