Measuring Transparent Liquids Using the ColorQuest XT
The instrument illustrated below is a ColorQuest XT. Measurements on an UltraScan VIS, UltraScan PRO, or ColorQuest XE would be carried out in a very similar fashion.
Batch-to-batch color consistency (or colorlessness, for some) is an important indicator of quality for many transparent liquids. Transparent liquids require special handling when being evaluated either visually or instrumentally. The color of a transparent sample changes when the path length is changed, so the path length must be fixed. Transparent liquids should be measured in a transmittance mode on a benchtop sphere instrument in order to assess the color of the liquids when light shines through them.
A HunterLab ColorQuest XT diffuse/8° spectrophotometer standardized in total transmittance (TTRAN) or regular transmittance (RTRAN) mode can be used to measure the transmittance of transparent liquids that are contained in optically-clear sample cells held in place over the transmission port or lens. This method is recommended by HunterLab for the measurement of transparent liquids.
The ColorQuest XT
The Application
Transparent liquids have several non-uniform characteristics that require compensating preparation and presentation techniques in order to ensure a repeatable sample measurement.
Liquids must be contained in and measured through a clear sample cell in order to be effectively made solid.
They are transparent--not opaque--and will be sensitive to path length changes, so a constant path length should be used.
Liquids may contain bubbles or nonhomogeneous areas that alter the color measurement, requiring the averaging of several readings with replacement.
| Recommended Color Scale | CIE L*a*b* or Hunter L, a, b as a full color descriptor |
| Recommended Single-Number Indices | YI D1925 (2/C), YI E313 when samples are near clear, APHA, ASTM D1500, Gardner, and/or Saybolt when samples are yellowish |
| Recommended Illuminant/Observer | D65/10° or C/2°. |
Measurement Method
Note: The pictures below illustrate standardization and measurement in TTRAN mode. RTRAN measurements are made in a very similar fashion, but with the sample placed at the lens rather than the transmission port.
| 1. Configure your software or the applet to read using the desired color scale, illuminant, and observer. | |
| 2. Install the transmission cell holder (HunterLab Part Number C02-1005-481) in the instrument's transmission compartment as described in your User's Manual. |  |
| 3. Standardize the instrument in the desired transmittance mode by following the software or touch screen prompts. Use of TTRAN mode is recommended if the samples have internal light scattering centers or a surface texture. Otherwise, either RTRAN or TTRAN mode may be used. You will need to read the black card, either at the transmission port or the lens, as your first step in standardization. Rest the card on the transmission shelf in the required orientation and close the transmission compartment door. |  |
| 4. Complete the standardization by removing the black card from the transmission compartment and replacing it at the transmission port or lens with a blank-filled cell of the same size as the one to be used for the sample measurements. (The blank should be distilled water or another clear solvent that is similar in composition to the sample.) |  |
| 5. Stir or shake the sample, if necessary, to homogenize it to its usual level. Then fill the sample cell to the top with the sample. Center the sample-filled cell over the transmission port (TTRAN) or lens (RTRAN) on the transmission shelf. Be careful to choose a cell path length appropriate for the sample and indices to be measured. The part numbers for the HunterLab glass transmission cells are as follows: 13-8573-20 for 50-mm, B04-1003-801 for 33-mm, 04-4592-00 for 20-mm, and 13-8573-40 for 10-mm. Disposable cells may also be used. Use enough liquid that the hole in the sphere (TTRAN) or the lens (RTRAN) is completely covered by the liquid. Wipe any excess liquid from the outside of the cell with a lintless wipe. Close the transmission compartment door. |  |
| 6. Take a single color reading of the sample. Empty and refill the sample cell and read the sample at least once more. Average the multiple color readings for a single color measurement representing its color. Averaging multiple readings with replacement between readings minimizes measurement variation associated with non-uniformity. | |
| 7. Record the average color values for the sample. |