Purpose: Provides background on the Gardner Index.
Answer:
The Gardner Index is a yellowness index. It was originally developed for color specification of resins. Initially, liquid standards of potassium dichromate, ferric chloride and cobaltous chloride, or potassium chloroplatinate were used. These solutions varied in stability and had a tendency to fade with time. Colorimetric values are now used to create glass standards as defined in ASTM Designation D1544 --Standard Test Method for Color of Transparent Liquids (Gardner Color Scale).
The glass standards are normally used for visual, subjective evaluation and assignment of Gardner color values. At HunterLab, the Gardner index is available in EasyMatch QC and Universal Software. A correlation between the Gardner Index and Yellowness Index E313 is used in the form of look-up tables. Measurements are made in total transmittance mode using a 10-mm or 20-mm sample cell. (Refer to your User's Manual for which one to use.) The samples to be measured should be clear liquids that are similar in hue to the Gardner glass standards. This method provides objective measurement and assignment of Gardner values.
Conditions for Measurement
Illuminant: C
Standard Observer Function: 2-degree
Transmittance and/or Reflectance: Transmittance only.
Formulas
No formula is employed in HunterLab instruments for calculating the Gardner Index. Yellowness Index E313 is calculated, and its corresponding Gardner value is looked up in a table and displayed.
Typical Applications
This index is generally used for describing the color of drying oils, varnishes, fatty acids, and resins.
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