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). Distilled water is a reference for Gardner 0. Most applications are between Gardner 0 and 8.
As described in ASTM D1544, these liquid standards were replaced by glass filters that are the basis for the visual Gardner Color comparator.
The instrumental correlation to the visual Gardner Color scale is defined in ASTM D6166. This is implemented in HunterLab EasyMatch QC software as “Gardner D6166 [C/2]”.
Sources for Liquid Gardner Standards:
RICCA Chemical Company, Arlington, TX 76094 USA +817-461-5601 www.riccachemical.com
All RICCA Gardner Standards are ordered through Fisher Scientific www.fishersci.com (search for “Gardner Color”).
Gardco/Paul N. Gardner Company, Pompano Beach, FL 33061 USA, +954-946-9454 www.Gardco.com
Paragon Scientific Ltd., Prenton, Wirral CH43 3DU, UK +44 (0)151 649 995 www.paragon-sci.com (search for “Gardner Color”)
Hach UK, Salford M50 1DL UK +0161 872 1487 http://uk.hach.com
Hach bought Dr. Lange (Germany) and with it got their LICO color measurement instruments that include measuring APHA/Pt-Co/Hazen and Gardner Color. Dr. Lange also had a side business of supplying liquid color standards for instrument performance qualification. Hach UK has picked this business up in Europe.
The ADDISTA Colour Set of 6 certified standard colour solutions for LICO (search for LZM282) consists of 3x50 ml APHA/Pt-Co/Hazen liquid color standards (levels of 20, 100, 200) and 3x50 ml Gardner liquid color standards (levels of 2, 5, 8).
Our EasyMatch QC software has a built-in 10 mm correlation for measuring both APHA/Pt-Co/Hazen and Gardner Color simultaneously on the same sample with the 10 mm cell path length filled with distilled water being APHA/Pt-Co/Hazen and Gardner = 0, representing no color.
How Best to Use a Liquid Gardner Color Standard
- A liquid Gardner Color Standard can best be used as a performance qualification step to verify your instrumental measurement of Gardner Color is consistent over time.
- Purchase a liquid Gardner Standard near or just above typical Gardner values for your samples.
- Standardize your HunterLab sphere instrument in Total Transmittance (TTRAN); Large Area of View (LAV); UV Filter Nominal mode using a 10 mm path length transmittance cell filled with DI water.
- As a PQ (Performance Qualification) step, leave the cell + DI water in place at the port, then measure the Gardner Color. 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 color values.
- As an optional second PQ step, measure the a Gardner Standard and baseline the Gardner Color which should closely match the assigned Gardner for the standard. Over time, the measured values of the liquid Gardner Color standard should closely match the original baseline Gardner Color values to help affirm that your instrument is consistent in measuring Gardner Color over time.
- Proceed to measure and report Gardner Color for your transparent liquid samples.
Industrial References for Gardner Color:
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).