How do you validate a APHA/Pt-Co/Hazen 500 liquid color standard?

As described in Section 6 of ASTM D1209, there are 2 criteria to validate a APHA/Pt-Co 500 standard: Continue reading

What is the stability of the APHA/Pt-Co/Hazen liquid color standards?

Per Section 6.2 of ASTM D1209 Standard Test Method for Color of Clear Liquids (Platinum Cobalt Scale):

“When properly sealed and stored the standards are stable for at least a year and do not degrade markedly for 2 years.”

 Our industrial experience is that if kept properly stoppered in amber bottles, the APHA/Pt-Co/Hazen visual color standards do not degrade significantly for longer than 2 years but this is the time frame that most sources reference as optimal.

If you have a dated APHA/Pt-Co/Hazen 500 liquid color standard, one validation method would be to see if it still meets the absorbance tolerance limits of ASTM D1209 Table 1, and is effectively clear (ASTM D1003 Haze% < 2).

A literature reference on stability of the APHA/Pt-Co/Hazen color standards can be found at:

Scharf, W. W., Ferber, K. H., and White, R. G., “Stability of Platinum-Cobalt Color Standards,” Materials Research and Standards, Vol. 6, No 6, June 1966 pp 302-304.


Do you know of an independent test lab that can measure APHA/Pt-Co/Hazen Color?

Contact the following and ask for “APHA/Pt-Co/Hazen Color testing per ASTM D1209 and D5386″.

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Can HunterLab instruments measure APHA/Pt-Co/Hazen Color above 500?

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ASTM Industrial Test Methods for visual and instrumental APHA Color Scale

FAQ: “Does HunterLab have any documentation to show that the UltraScan VIS is compliant with ASTM 1209. One of our customers is having a problem regarding the method. Their client is using the manual visual method for performing the ASTM 1209 color test method whereas they use the UltraScan VIS. Can you explain the difference?” Continue reading

What standard do I use to verify Yellowness Index Performance?

There are no physical liquid standards specifically designed to verify the Yellowness Index of liquid samples over time. Yellowness Index is defined as a mathematical function such that a perfect clear of 100% transmission, typically represented by the transmission cell filled with DI water, will have a YI value of 0.

However, a good workaround solution is to use a very stable APHA/Pt-Co liquid standard in the yellowness range of your product as an application diagnostic to monitor your liquid measurement over time. Continue reading

References for Hazen Color Scale

The original references were written by Allen Hazen, a chemist who first defined APHA/Pt-Co/Hazen color scale for the evaluation of water quality on behalf of the American Public Health Association:

Hazen, A. A new color standard for natural waters, American Chemist Journal (14:300), 1892.

Hazen, A. The measurement of the colors of natural waters, American Chemist Journal (18:264), 1896.


Industrial Test Methods referencing the Hazen Color Scale

ISO 2211:1973 Liquid chemical products – Measurement of colour in Hazen units (platinum cobalt scale) is an ISO method that references both Hazen and platinum cobalt color and was subsequently replaced by DIN EN ISO 6271.