Measuring the color of fabric samples is important for the following reasons:
Fabrics may be translucent and are very often directional. Therefore, special presentation techniques are required to provide repeatable results. In general, several layers of sample should be presented to the instrument together. Also, several readings of the fabric should be averaged for the final result, preferably with rotation of the sample between measurements.
A HunterLab MiniScan EZ 45/0 LAV spectrophotometer can be used to measure the reflectance of fabric samples, usually folded into multiple layers. This is the method advocated by HunterLab for the measurement of fabric if a LabScan XE with UV control is not available.
Fabrics have several non-uniform characteristics that require compensating preparation and presentation techniques in order to ensure a repeatable sample measurement.
Fabrics may not be completely opaque and may look different when backed with differently colored samples. Using a sufficient sample thickness (several layers) and a sample backing will minimize these effects.
Fabrics are usually directional and sometimes non-homogeneous, requiring the averaging of several readings with rotation.
Fabrics (particularly white ones) may be slightly fluorescent, which means that they will be sensitive to the UV content of the light source. If this is the case, consideration should be given to using an instrument with a UV control option. (See Measuring Fabric Using the LabScan XE.)
|Recommended Color Scale||CIE L*a*b* or Hunter L, a, b as a full color descriptor|
|Recommended Single-Number Indices||DEcmc for indication of total color difference, Shade number for dividing multiple samples into shade groups|
|Recommended Illuminant/Observer||D65/10°. C/2° may also be used.|
|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 to set the bottom of scale. Make sure the black glass is in solid contact with the port.|
|3. Complete the standardization using the calibrated white standard.|
|4. It is possible to measure a single layer of fabric. If you do, you must specify the background (usually a white backing tile) as a condition of measurement. Place the white backing tile, white side up, on a table top or other flat surface. Lay the single fabric layer across the face of the tile and stretch it flat and smooth.|
|5. Place the instrument port on top of the fabric and measure it as indicated in step number 8.|
|6. The more common practice is to fold the fabric into multiple layers until it is effectively opaque. Four layers (two folds in half) are usually sufficient.|
|7. Place the white backing tile, white side up, on a table top or other flat surface and cover it with the folded sample. Place the instrument port on top of the fabric. The white tile provides a solid surface and consistent background. If necessary, pull the fabric taut and back around the tile to ensure that it does not pillow into the port.|
|8. Take a single color reading of the fabric backed by the tile. Rotate the fabric 90° and read the fabric at least once more. Average the multiple color readings for a single color measurement representing the color of the lot. Averaging multiple readings with rotation between readings minimizes measurement variation associated with directionality and non-homogeneous color. A common practice is to average four readings with rotation, with one reading made in each quadrant.|
|9. Record the average color values representing the fabric color.|