Measuring Small Items
The instrument illustrated below is a ColorQuest XE. Measurements on an UltraScan PRO or UltraScan VIS would be carried out in a very similar fashion.
The color of small pieces must often be assessed, primarily to ensure lot-to-lot color consistency. In some cases, a flat area large enough to cover the sample port may be available so that the pieces can be measured individually as described in Procedure #1, below. Other times, a sampling of a number of pieces should be measured together in order to obtain an overall average of the color for the batch. Several readings of the individual item or group of items should be averaged for the final result, preferably with replacement of the sample between measurements.
By convention, the instrument geometry most commonly used to measure the color of small items is a directional (45°/0° or 0°/45°) geometry instrument such as the LabScan XE (preferred) or ColorFlex 45/0. However, if very tight repeatability is not required, it is also possible to measure item color using a diffuse geometry instrument such as the HunterLab ColorQuest XE, UltraScan PRO, or UltraScan VIS spectrophotometer with appropriate sample devices.
The ColorQuest XE
The Application
Small items have several non-uniform characteristics that require compensating preparation and presentation techniques in order to ensure a repeatable sample measurement.
The available measurement area may be very small and/or curved. The proper size port insert must be used to limit the area measured by the instrument, and a flat area must be located for measurement, or else a group of samples must be measured through the clear window of a glass cell or dish in order to be effectively made into a solid.
These pieces are irregular in size and shape, requiring the averaging of several readings with replacement.
The pieces may be translucent — not opaque — and will be sensitive to ambient light and to small differences in the optical configuration of the instrument. Using a sufficient sample thickness and/or constant background will minimize these effects.
They may be slightly fluorescent, which means that they will be sensitive to the UV content of the light source. If fluorescence is an issue, use of the UV control option is recommended.
Note: If inter-instrument agreement is a concern when measuring translucent pieces, all the instruments used for those measurements MUST be the same model to minimize measurement differences.
| Recommended Color Scale | CIE L*a*b* or Hunter L, a, b as a full color descriptor |
| Recommended Single-Number Index | YI E313 for indication of yellowness, WI E313 for indication of whiteness, dE CMC for visible total color difference. |
| Recommended Illuminant/Observer | D65/10°. C/2° may also be used. |
Measurement Methods
Procedure #1: Measuring Small Items Individually.This method is preferred so long as a relatively flat sample area is available that can completely cover the opening in the port plate chosen for measurement. The small area view (SAV) option must be available with the instrument in order to use this measurement method.
| 1. Configure your software to read using the desired color scale, illuminant, and observer. | |
| 2. Install the small area view port plate and standardize the instrument in RSIN mode for the smallest area view available in your software. If the area of the sample to be measured will not completely cover the hole in this port plate without presenting excessive curvature to the instrument, you may install the 4-mm optional port plate (HunterLab Part Number A02-1011-184 for ColorQuest XE, UltraScan PRO, and UltraScan VIS, A02-1010-838 for UltraScan XE) instead. Other special port plates are also available that may suit your needs, such as round tablet holders (HunterLab Part Number CMR-2788 for ColorQuest XE and UltraScan VIS, CMR-2513 for UltraScan XE, CMR-2927 for UltraScan PRO) and caplet holders (HunterLab Part Numbers CMR-2880 and CMR-2944 for ColorQuest XE and UltraScan VIS; multiple sizes). First standardize on the light trap, then the white tile. |   |
| 3. Locate a flat area on the sample, place it over the reflectance port, and hold it in place using the sample clamp with the white disk installed to back the sample. Make sure that the area of the sample to be measured faces the port and completely covers the port opening. Use the retroviewer (included with UltraScan XE, UltraScan PRO, and UltraScan VIS, HunterLab Part Number RETRO-CQXE for ColorQuest XE), if available, to check that the desired sample area is correctly positioned over the port opening. |  |
| 4. Take a single color reading of the sample. Rotate the sample 90° or move the sample to another area containing the same color and read it at least once more. Alternatively, you may measure another part of the same color. Average the multiple color readings for a single color measurement. Averaging multiple readings with rotation or movement between readings allows you to better estimate the color of the piece as a whole. | |
| 5. Record the average color values. |
Procedure #2: Measuring Small Items in Batches. This method should be used to obtain an overall average of the color of a batch, particularly when samples are too small or too curved to be measured using Procedure #1.
| 1. Configure your software to read using the desired color scale, illuminant, and observer. | |
| 2. Standardize the instrument for RSIN and the large area of view, first using the light trap... |  |
| 3. ...then the white standard tile that came with the instrument. | |
| 4. Scoop up or pour pieces from the sample batch to completely fill the 50-mm glass cell (HunterLab Part Number 13-8573-20) or a glass or plastic Petri dish with an available lid (not available through HunterLab). The constant sample thickness makes the translucent, irregular pieces effectively opaque for reflectance measurement. If you are using a Petri dish, also place the cover firmly on the dish. |   |
| 5. Lower or remove the sample clamp. If you will be using a sample cell to hold your sample, also install the shelf of the reflectance sample shelf with light cover (HunterLab Part Number B02-1005-172) at the reflectance port. |  |
| 6. Place the filled cell or covered dish flush against the reflectance port and hold it in place using the sample clamp (dish only). The pieces will be read through the clear window of the cell or dish. |   |
| 7. Take a single color reading of the pieces. Dump, refill, and read the pieces at least five times from the same batch (or, if you are using a Petri dish, present a different area of the dish to the instrument). Average the five color readings for a single color measurement representing the color of the batch. Averaging multiple readings minimizes measurement variation associated with non-uniform samples. | |
| 8. Record the average color values for the sample batch. |