Like turbidity measurement, photometric color measurement is an important parameter for assessing the quality of liquids. To ensure the comparability of measurement results, standards for the photometric measurement of liquids have been established for a wide range of applications. On this page, you will find information on the most common color scales.
The American Public Health Association (APHA) has published several testing procedures for water, wastewater, and chemistry, including a method for determining the yellowness of liquids. This method relies on a visual comparison of the liquid against a platinum-cobalt reference solution. The platinum-cobalt scale—also known as the APHA color scale—is a widely used method for determining the color of liquids.
Since the color value is expressed in Hazen units or mg/L Pt, the term “Hazen color value” is also commonly used. The standard for APHA color measurement of liquid media was issued by the ISO in 1973 (ISO 2211: Measurement of colour in Hazen units (platinum-cobalt scale)) and replaced the outdated DIN 53409 standard from 1967. However, ISO 2211 did not offer sufficient precision for certain industrial applications and was therefore replaced in 1981 by the more precise DIN ISO 6271.
| 430 nm / path length 10 mm | 0.115 AU |
|---|---|
| 455 nm / path length 10 mm | 0.135 AU |
| 480 nm / path length 10 mm | 0.115 AU |
| 510 nm / path length 10 mm | 0.06 AU |
When calibrating inline photometers using the Pt/Co solution, note that the solution reacts with the nickel in the stainless steel and loses its color.
Preparation of a stock solution (Pt/Co color value 500 Hazen):
Dissolve 1.245 g of potassium hexachloroplatinate and 1.000 g of cobalt(II) chloride hexahydrate in 100 ml of concentrated, chemically pure hydrochloric acid (d = 1.19) (heating if necessary).
Dilute to 1 liter with distilled water.
Please note that this procedure must only be carried out in suitably equipped laboratories by qualified personnel, in compliance with safety regulations.
Also, observe the safety instructions regarding the handling of the prepared stock solution.
ASTM International (formerly the American Society for Testing and Materials) is an international standards organization based in the USA. It publishes technical standards for goods and services. ASTM was founded in 1898 by a group of scientists and engineers led by Charles Benjamin Dudley.
By 2005, there were more than 12,000 ASTM standards. Color scales such as Gardner, Saybolt, or Rosin are also defined within ASTM standards. Other institutions—such as the Institute of Petroleum (IP) or Malaysian Standards (MS)—have adopted identical specifications in their own sets of standards.
ASTM D 1500, ASTM D 6045, ISO 2049, IP196
A color scale for petrochemical products, defined by 16 glass standards with specific transmission and chromaticity characteristics. The standards are graduated in 0.5 ASTM increments, ranging from 0.5 ASTM (lightest shade) to 8.0 ASTM (darkest shade). This unit serves as a quality parameter for products such as lubricating oil, heating oil, diesel, and kerosene.
ASTM D 156, ASTM D 6045
The Saybolt color scale is used to measure lightly colored petrochemical products—such as aviation fuel, kerosene, etc.—that fall below a color value of 0.6 on the ASTM D 1500 scale. The scale ranges from -16 (dark) to +30 (light), with the color value derived from the height of the sample column during a visual comparison against three defined glass standards.
ASTM D 1544, ASTM D 6166, DIN EN ISO 4630-1, MS 817 Part 10
MS = Malaysian Standards for palm oil testing / Homepage: Malaysian Palm Oil Board
Color value ranging from pale yellow to red, defined using glass standards with specific transmission and chromaticity characteristics. All standards are numbered from 1 to 18, with 1 representing the lightest shade and 18 the darkest.
DIN EN ISO 4630 defines Gardner color values 1–8 using potassium chloroplatinate solutions, and color values 9–18 using solutions of iron(III) chloride, cobalt(II) chloride, and hydrochloric acid.
The Gardner scale is used as a quality parameter for chemicals, oils, and resins; however, it exhibits a relatively large jump in color between values 8 and 9.
ASTM D 509
The Rosin color grade is arguably the most widely used method for determining the color quality of resins. The basic scale comprises 15 color standards ranging from yellow to reddish-orange. Each colored glass standard is assigned a letter designation: XC (lightest shade), XB, XA, X, WW, WG, N, M, K, I, H, G, F, E, and D (darkest). FF is an additional special standard for resins from dark woods. The colored glass standards are mounted in cubes to allow for direct comparison with resin samples.
The European Brewery Convention (EBC) promotes, among other things, brewing science activities in Europe. Parameters such as beer turbidity, color, and bitterness are expressed in EBC units. The organization was founded in 1947 to support malting and brewing science. Its aim was—and remains—to develop analytical methods that ensure beer quality and promote consistently high standards for raw materials and brewing processes.
Over the years, this successful work led to the standardization of many processes, resulting in improved product safety and process hygiene. Against this backdrop, the EBC established a Technology and Engineering Forum in 1990, tasked with developing the simplest possible technical procedures to optimize production and quality assurance within the malting and brewing industries.
Color is a key parameter for monitoring the quality of beer and wort during the brewing process. To determine the color of beer and wort, light absorption is measured at 430 nm (MEBAK 2.16.2, EBC 9.4). In the laboratory, samples are filtered to a turbidity value of less than 1 EBC prior to color determination.
Subsequently, the absorbance is measured using a 10 mm cuvette.
If necessary, the sample is diluted until the absorbance falls below 2 absorbance units (E430). Finally, the EBC color value is calculated as follows: E430 × 25 × dilution factor.
Like the EBC, the ASBC publishes standard methods and has released calibration units for measuring color in beer and wort. The ASBC unit is rarely used in Europe and has largely been replaced by the EBC unit even in the USA. The ASBC color value can be derived directly from the EBC color value: 1 ASBC = 0.375 EBC color + 0.46.
AOCS Cc 13e, AOCS Cc 13j, ISO 15305, MS 252: Part 16, IP 17 Method A
Lovibond color values are based on a comparison with 84 glass standards of varying optical density (Neutral N) and color (Red, Yellow, Blue). These colored glasses range from lightly tinted to fully saturated. Color filters (R, Y, B) and neutral filters (N) are combined until the hue and brightness match the product sample.
The result is a set of RYBN glasses that define the Lovibond® color (RYBN units). Since millions of filter combinations are possible with this method, virtually any color can be determined.
Primary applications include edible oils and fats, as well as chemicals and pharmaceutical products. Today, the Lovibond color value for edible oils is also determined photometrically, typically by measuring specific fixed red and yellow values. In general, the color of edible oil is expressed numerically in terms of Lovibond Red and Lovibond Yellow.
ICUMSA GS1-7, ICUMSA GS2/3-9
ICUMSA describes a photometric method for measuring the color of filtered sugar solutions and serves as a measure of sugar purity in dissolved form. The method measures the sample’s transmittance at a known sugar concentration (Brix value). The specified measurement wavelengths are 420 nm for white and lightly colored sugar, and 560 nm for dark sugar. The ICUMSA color value is expressed in RBU (Reference Base Units). The lower the ICUMSA value in RBU, the whiter the sugar.
ICUMSA online
Example:
Sugar with an ICUMSA value of 46 RBU indicates pure white sugar of the highest quality.
An ICUMSA value of 150 RBU indicates a darker sugar of lower quality.
DIN EN ISO 7887-3
The SAC value—spectral absorption coefficient—describes the yellow coloration of water during the treatment of drinking water, wastewater, and process water. The measurement is expressed in m⁻¹ (absorbance per meter of path length [Abs/m]). This measurement method is typically used to monitor water treatment processes.
Color assessment according to DAB 1996
Purity requirements of the German Pharmacopoeia: The German Pharmacopoeia contains regulations that supplement those of the European Pharmacopoeia. For instance, it governs analytical methods or herbal substances that are not in common use across all member states of the European Pharmacopoeia Commission. The European Pharmacopoeia establishes standards for areas that are widespread throughout Europe or require uniform regulation.
Klett color value (cosmetic industry, raw material assessment)
Hess-Ives color value (cosmetic industry, color assessment of fat derivatives)
The measurement units listed here are not based on comparative calibration standards. Transmission and absorption are derived directly from light intensity.
In physics, transmission is a measure of a medium’s permeability to waves—such as sound waves or electromagnetic waves (IR, VIS, UV light, etc.)—where 100% of the emitted light intensity reaching a photometer’s receiver optics corresponds to 100% transmission. If the light intensity is halved (e.g., due to turbidity in the product sample), the transmission value is also halved to 50%.
Absorption values are calculated from the logarithm of the reciprocal of transmission; they also describe the attenuation of radiant power as optical radiation passes through a medium. The absorption value typically follows the Beer-Lambert law and is proportional to the path length traversed by the beam and the quantity of absorbing substances (proportional to concentration).
% (Percent transmission)
A (Spectral absorbance)
Spectral absorbance is also referred to as:
EXT (Extinction)
CU (Concentration Unit)
AU (Absorption Unit)
OD (Optical Density)
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