Application Note
AN 1011.00
Measuring the Color of
Non-Opaque & Textured Samples
Abstract
An Ideal Sample is...
• opaque or transparent (not translucent)
• solid (not liquid)
• flat (not curved)
• smooth (not textured)
• homogenous (all the same color)
• non-thermochromic (color does not
change with temperature)
• non-hygrochromic (color does not
change with humidity or moisture)
• non-directional (color does not change
with sample orientation)
A repeatable color measurement is essential to
successfully quantify the color of your product.
If you have an ideal sample like a color tile or
glass filter it is easy to make a repeatable color
measurement. Most real world samples are less
than ideal, but can be measured with success if
good color measurement techniques are used. This application note looks at guidelines for
presenting liquids, semi-solids, powders, pellets
and loose fibers to achieve repeatable results.
Measuring the Color of Non-Opaque & Textured Samples
AN 1011.00
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Challenge: To select the optimal color measurement technique and derive a repeatable color measurement
method based on the type of sample and instrument geometry available.
For optimal color analysis of samples, the selection of appropriate accessories and proper placement of the
sample in the optical path is important. Once a measurement method has been defined, this procedure be
followed for all subsequent color measurements.
Application #1: Liquids
Accessories: Glass transmittance cell or sample cup.
Transparent, translucent, and opaque liquids
must be placed in a container for measurement.
Transparent liquid samples are poured into a
glass transmittance cell or vial, and measured in
the transmittance compartment (Figure 1). The
preferred technique for translucent and opaque
liquids is to measure them in reflectance using a
sample cup on a directional instrument such as the
LabScan XE or ColorFlex EZ 45°/0°. Alternatively,
translucent and opaque liquids can be measured
at the reflectance port of a diffuse/8° instrument
such as the ColorQuest XE, UltraScan PRO, or
UltraScan VIS using a 50 mm path length cell.
Application #2: Translucent Semi-Solids
Accessories: Glass sample cup or transmittance
cell.
Translucent semi-solids, such as yogurt, baby food,
and salad dressings, are normally measured
in a glass sample cup using a directional type
instrument such as the LabScan XE or ColorFlex EZ
45°/0° (Figure 2), or placed in a glass transmittance
cell and measured at the reflectance port of a
diffuse/8° sphere instrument (Figure 3).
Figure 1. Transparent liquid measured in transmittance using a
clear glass vial.
Figure 2. Semi-solid yogurt sample measured throught the
Figure 3. Translucent liquid can also be read in a 50 mm thick
bottom of a sample cup on a directional 45°/0° instrument.
cell on a diffuse/8° sphere instrument.
Measuring the Color of Non-Opaque & Textured Samples
Application #3: Powders
Accessories: Powder press, glass sample cup or
transmission cell.
In measuring powders, the best technique for color
analysis is to make them more solid. One technique
is to press the powder into a smooth plaque and
measured on a directional instrument such as the
LabScan XE in the port-down or port-up orientation.
An alternate technique is to measure loose powder
through the bottom of a sample cup (Figure 4).
Powders can also be placed in a 50 mm glass
transmission cell and measured at the reflectance
port of a diffuse/8° sphere instrument in RSEX
(Reflectance Specular Excluded) mode.
AN 1011.00
Figure 4. Measuring the color of a loose powder in a sample cup
on a directional 45°/0° instrument.
Application #4: Pellets or Large Particulates
Accessories: Glass Sample Cup.
Plastic pellets and similar granular items such as rice
and sugar can be measured through the bottom
window of a sample cup making the granular
sample effectively into a solid. These samples are
typically measured using a directional geometry
instrument such as the LabScan XE or ColorFlex EZ
45°/0°. As an alternate but less preferred technique,
pellets or large particulates can be placed in a
50 mm glass transmission cell and measured at the
reflectance port of diffuse/8° sphere instrument in
RSEX (Reflectance Specular Excluded) mode.
Application #5: Textiles
Accessories: Compression Cell & Sample Cup.
Like powders, loose textile fibers trap light and are
not solid. However, if flattened against the glass
window of a sample cup using an air-driven
compression plunger, loose fibers effectively
become a solid. A compression cell set is available
for the ColorQuest XE, LabScan XE, UltraScan PRO,
and UltraScan VIS.
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Figure 5. Dried green peas presented to a ColorFlex 45°/0°
through the bottom of a clear plastic dish for color analysis.
Figure 6. Loose textile fibers placed in a sample cup, then
compressed with air.
Measuring the Color of Non-Opaque & Textured Samples
AN 1011.00
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Conclusion
The guidelines presented here promote the repeatable and reproducible
measurement of color for a variety of non-uniform samples. Once an optimal
measurement method has been established, consistent measurements from
lot-to-lot and site-to-site can be made.
References
AATCC Evaluation Procedure 6 - Instrumental Color Measurement.
ASTM E179 Standard Guide for Selection of Geometric Conditions for
Measurement of Reflection and Transmission Properties of Materials.
Hunter, Richard S., and Harold, Richard W., The Measurement of
Appearance, 2nd Ed., John Wiley and Sons, Inc. New York, NY USA 1987.
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About Hunterlab
HunterLab, the first name in color measurement, provides ruggedly dependable, consistently
accurate, and cost effective color measurement solutions. With over 6 decades of experience
in more than 65 countries, HunterLab applies leading edge technology to measure and
communicate color simply and effectively. The company offers both diffuse/8° and a complete
line of true 45º/0º optical geometry instruments in portable, bench-top and production in-line
configurations. HunterLab, the world’s true measure of color.
© Hunterlab 2014
Hunter Associates Laboratory Inc.,
11491 Sunset Hills Road, Reston, VA 20190-5280 USA
[email protected]
www.hunterlab.com