Measuring Flat, Translucent Solids Using the LabScan XE

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 benchtop 45/0 or 0/45 instrument such as the LabScan XE.

A HunterLab LabScan XE 0/45 spectrophotometer can be used to measure the reflectance of flat, translucent solids that are placed over the sample port and either backed by the sample clamp or an uncalibrated white tile or folded or stacked into multiple layers until opaque. This method is recommended by HunterLab for the measurement of flat, translucent solids, including such items as paper and plastic plaques.

The LabScan XE

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, folding it, or stacking multiple layers will make the sample effectively opaque and provide a constant background for the measurement. Using a larger port size than area of view (if possible) will cause all the light scattered by the sample to be reflected back through the sample and measured.

• 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. Use of the UV control option is recommended.

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 to read using the desired color scale, illuminant, and observer.
2. Standardize the instrument using the the largest port size possible for which the sample can completely cover the hole in the port plate and a smaller area view than that port size (if the variable sample illumination option was purchased). (For instance, use the 2.0-inch port plate and indicate the 1.0-inch area view to the software.) First standardize on the black glass, then the white tile. The instrument may be standardized with the port up, forward, or down using the port-down stand (HunterLab Part Number D02-1009-350).
3. Center the sample to be measured over the sample port and back it using the white disk on the sample clamp (HunterLab Part Number D02-1009-200) or an uncalibrated white tile (HunterLab Part Number 11-0108-50). Make sure that the area of the sample to be measured faces the port and completely covers the port. Alternately, fold the sample (for paper) or stack a set number of layers (for plaques) at the sample port.
4. 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.
5. Record the average color values.