Measuring Flat, Translucent Solids Using the MiniScan EZ
Lot-to-lot or piece-to-piece color consistency is an important indicator of quality for many colored items. Flat, translucent items can be easily measured at the sample port of a portable 45/0 or Diffuse/8° instrument such as the MiniScan EZ.
A HunterLab MiniScan EZ spectrophotometer can be used to measure the reflectance of flat, translucent solids when the instrument sample port is placed over the sample and a constant white backing such as an uncalibrated white tile or multiple layers of folded or stacked sample are read. This is the method advocated by HunterLab for the measurement of flat, translucent solids, including such items as paper and plastic plaques, if a ColorQuest XE, LabScan XE, UltraScan PRO, or UltraScan VIS with UV control is not available.
The MiniScan EZ
The Application
Flat, translucent solids may have several non-uniform characteristics that require compensating preparation and presentation techniques in order to ensure a repeatable sample measurement.
As they are not opaque, translucent samples exhibit light trapping, and will be sensitive to ambient light and to small differences in the optical path of the instrument. Backing the sample or folding or stacking layers will make the sample effectively opaque and provide a constant background for the measurement.
The samples may be directional, requiring the averaging of several readings with rotation.
The samples (particularly white ones) may be fluorescent, which means that they will be sensitive to the UV content of the light source.
| Recommended Color Scale | CIE L*a*b* as a full color descriptor, Yellowness Index and Whiteness Index often used for white samples. |
| Recommended Illuminant/Observer | D65/10°. C/2° may also be used. |
Measurement Method
| 1. Configure your software or the instrument firmware to read using the desired color scale, illuminant, and observer. | |
| 2. Standardize the instrument, first using the black glass or light trap to set the bottom of the scale. Make sure the black glass is in solid contact with the port or the light trap completely covers the port. |  |
| 3. Complete the standardization using the calibrated white standard. |  |
| 4. Place the uncalibrated white tile (HunterLab Part Number 11-0108-50), white side up, then the sample, with the side to be measured facing up, on a table top or other flat surface. Alternately, fold the sample (for paper) or stack a set number of layers (for plaques) on a flat surface. |   |
| 5. Place the instrument port on top of the sample, making sure that it is completely covered by the area to be measured and is flat against it. |  |
| 6. Take a single color reading of the sample. Rotate the sample 90° and read it at least once more. Average the multiple color readings for a single color measurement representing its color. Averaging multiple readings with rotation between readings minimizes measurement variation associated with non-uniformity or texture. | |
| 7. Record the average color values. |