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.


Is it possible to create ASTM traceable haze standards above 30%?

The current, available ASTM D1003 Haze Standards have nominal Haze% values of 1, 5, 10, 20 and 30 with air (transparent solids) or the transmission cell filled with DI water being 0 (transparent liquids). Here are some thoughts on further options. Continue reading

Measuring the Color of Clear Liquids

Liquid Fragrance Sample

Liquid Fragrance Sample

One application that often comes up is measuring the color of clean liquids such as the fragrance sample seen above. This liquid fragrances is clear and looks almost like water. Fragrances such as this are often added to cleaning supplies, air fresheners, or other consumer products. One of the problems that this type of sample can experience is that the chemistry of the liquid fragrance solution can go bad and it will start to visually yellow. This is a concern of the manufacture because if the liquid fragrance yellows it cannot be added to the end product. Continue reading

Human Observers

Human Observer Experiment

Human Observer Experiment

This is the final blog note article in our series describing the Visual Observing Situation Model in which we will discuss human observers. Previously we discussed how the illuminants and objects are quantified to help measure color.

In the human eye there are rods that are responsible for low light vision and cones that are responsible for color vision functioning at higher light levels. There are three types of cone sensitivities: red, green, and blue. To effectively quantify how the human eye sees color a standard observer (a table of numbers) must be derived.

To develop the standard observer a set of experiments were run to quantify the ability of the human eye to see color. These experiments had a person looking at a white screen through an aperture having a 2 degree field of view with half of the screen illuminated by a test light. The person then adjusted the amount of 3 primary colored lights on the other half of the screen until they matched the test light color. This process was repeated for all colors across the visual spectrum.

The experiments resulted in a x bar, y bar, and z bar function that became the CIE 1931 2˚ Standard Observer. These functions quantify the red, green, and blue cone sensitivity of the average human observer. After these initial experiments were conducted it was found that the cones are spread beyond the area in the eye they were believed to be concentrated. The experiments were re-done in 1964 resulting in the CIE 1964 10˚ Standard Observer.

These experiments provided a table of numbers that effectively quantifies how the human eye sees color and quantifies the last piece of the Visual Observing Situation model. With all three pieces of information the way color is perceived by human observers can now be quantified.


How do you quantify color?

Visual Observing Situation Model

Visual Observing Situation Model

HunterLab instruments measure the color as it relates to the quality of the product. To be able to begin to measure and quantify color we have to know more about why colors appear as they do. As humans we all see and perceive color differently; this is because the human perception of color is a psychophysical response. The visual observing situation model shown above illustrates the three components necessary for the perception of color. Continue reading

ColorFlex EZ Coffee Meter

ColorFlex EZ Coffee Meter

ColorFlex EZ Coffee Meter

Recently HunterLab developed the ColorFlex EZ Coffee meter. The color of coffee is important because it is predominantly used to assess the degree of roasting. The CFEZ Coffee is specially designed to measure the color of roasted coffee grounds, freeze-dried coffee, and instant powders.

Specialty scales have been added to the CFEZ to help easily determine the quality of the coffee being measured. These scales include the HunterLab Coffee Color Index (HCCI), SCAA (Specialty Coffee Association of America) Number, and SCAA Roast Classification. The CFEZ Coffee also now comes with a PQ (performance qualification) coffee tile. This tile allows the user to check the CFEZ Coffee instrument to ensure that it is reading color as expected.

The CFEZ Coffee has been designed to consistently measure lot to lot differences to improve upon consistency and batch to batch production quality. By using the CFEZ Coffee it will be easy for to define the degree of roasting. The CFEZ Coffee gives users a quick and easy way to quantitatively determine the quality of their coffee.

You can find more information for the CFEZ Coffee at the product page on our website.

Measuring Citrus Juices

Measuring CitrusColor is often used as an indication of quality and freshness for food products; this especially applies to orange juice where a red-orange color is preferred. The HunterLab ColorFlex EZ instrument is widely used in the citrus industry to objectively measure the color of juices.

Originally citrus juice manufactures used subjective methods for evaluating sample color. They would perform visual comparisons of orange juice in a standard glass tube to a set of United States Department of Agriculture (USDA) plastic comparators also in glass tubes. The results of this method were often inconsistent and unreliable. Continue reading