The original definition of 1958 Gardner Color Scale was a series of 18 liquid color standards ranging from near clear, a light yellow (Gardner 1) to a dark brown (Gardner 18).
As described in ASTM D1544, these were replaced by glass filters and form the basis for a visual color comparator. The instrumental correlation to the visual Gardner Color scale is defined in ASTM D6045.
Sources for Liquid Gardner Standards:
Gardco – Paul N. Gardner Company, Pompano Beach, FL 33061-6688 USA +954-946-9454 gardco.com
How Best to Use a Liquid Gardner Color Standard
A liquid Gardner Color Standard can best be used to verify your instrumental measurement for consistency in measuring Gardner Color over time.
- Purchase a liquid Gardner Standard near or just above typical Gardner values for your samples.
- Standardize your HunterLab sphere instrument in Total Transmission (TTRAN) Large Area of View (LAV) mode using a cell of 10-mm path length filled with DI water.
- As a Performance Qualification (PQ) step, leave the cell in place at the port, then measure the Gardner Color of DI water. If the instrument is set up correctly, the measured Gardner Color should be = 0, with corresponding L* = 100.0, a* = 0.0, b* = 0.0 values.
- As an Application Diagnostic, measure the liquid Gardner Standard and baseline the Gardner Color which should closely match the assigned Gardner for the standard. Measured over time, the measured values of the liquid Gardner Color standard should very closely match the original baseline Gardner Color values. This helps affirm that your instrument is consistent in measuring Gardner Color over time.
- Proceed to measure and report Gardner Color for your samples.
ASTM D1544 Standard Test Method for Color of Transparent Liquids (Gardner Scale)
ASTM D6166 Standard Test Method for Color of Naval Stores and Related Products (Instrumental Determination of Gardner Color).