ISO 7724 Paints and Varnishes - Colour Measurement

The “ISO 7724 Paints and varnishes - Colour measurement” standard published by the International Organization for Standardization (ISO) consists of the following sections published under the same title:

• The standard "ISO 7724-1 Part 1: Principles" describes the colorimetric terms and basic requirements for determining the color coordinates of paint films. Among the various color coordinates proposed by the CIE, the color coordinates in the CIE 1964 Supplementary Standard Colorimetric System and the color coordinates in the color space specified in the CIE 1976 Standard for measurements on paint films are compatible with this standard. However, this standard has been withdrawn.

The purpose of this standard is to define terms such as chromaticity, tristimulus values, and standard illuminants (e.g. D65 for daylight) and observers (e.g. CIE 2° or 10° standard observer).

This standard specifies the use of calibrated instruments (spectrophotometers or colorimeters) and standard conditions such as imaging geometry (e.g., 45°/0° or diffuse/8°) to ensure accurate color measurement.

Measurements must take into account surface properties (e.g. gloss, texture) and be performed under controlled lighting conditions.

• The standard "ISO 7724-2 Part 2: Color measurement" describes a method for determining the color coordinates of paint films. This method applies to paint films that appear to be a single color (monochromatic) when examined with normal vision. Paint films that do not completely obscure a opaque substrate can be measured using this method. All other paint films are excluded from the scope of this standard. Luminescent paint films, transparent paint films, and translucent paint films (e.g., for displays or lamp lenses), retroreflective paint films (e.g., for traffic signs), and metallic paint films are excluded from the scope of this standard.

Tristimulus values ​​can be measured by one of the following methods:

• Measurement of the spectral photometric properties (spectral reflectances or spectral reflectance factors) of the paint film with a spectrophotometer and calculation of tristimulus values
• Measurement of tristimulus values ​​with a tristimulus calorimeter.

As described in the ISO 7724-1 standard, chromaticity coordinates or color coordinates in the approximately uniform CIE 1976 (L*a*b*) color space are calculated from the tristimulus values.

One of the illumination and imaging measurement conditions should be selected taking into account the surface texture, the reflective properties of the paint film being tested and the information to be obtained by the measurement.

The purpose of this standard is to measure the colour of a paint film in terms of CIE colour coordinates (e.g. Lab* or XYZ values).

A paint film sample is typically prepared by applying it to a substrate and curing it under specified conditions. A spectrophotometer or colorimeter is used to measure the sample's spectral reflectance or transmittance. By comparing the sample to a reference standard (e.g., a white tile or a specified color), color coordinates are calculated using CIE standards. The results are recorded in a standardized color space, such as CIE Lab*, where L* represents lightness, a* represents red-green, and b* represents yellow-blue.

Spectrophotometers or colorimeters with traceable calibration are used in the tests.

• The standard "ISO 7724-3 Part 3: Calculation of color differences" describes a method for the quantitative colorimetric assessment of small differences between paint films. The CIE 1976 color difference formula has proven to be of practical value and has been specified for this application. The principle is based on calculating the differences in color, brightness, color saturation, and hue between the paint films of a test sample and those of a reference sample in the CIE 1976 color space. Applying the two specified methods yields comparable results for high-gloss paint films. However, this standard has been withdrawn.

The purpose of this standard is to measure the color difference between a sample and a reference to determine whether it is within acceptable tolerances.

The color coordinates of both the sample and the reference are measured using the methods of the ISO 7724-2 standard. The color difference is calculated using a formula, typically the CIE 1976 Lab* color difference equation. The total color difference value is compared to the specified tolerances. This determines whether the sample meets the required color specification.

This method is used to evaluate batch-to-batch consistency or color shift over time. Testing is performed in controlled environments using calibrated instruments to ensure repeatability and accuracy.

Essentially, the ISO 7724 standard is a standard that provides methods for measuring and determining the colour of paints, varnishes and related coatings and consists of three parts that include procedures for colour measurement, comparison and specification:

• The ISO 7724-1 standard describes colorimetric terms and basic requirements for color measurement, including the use of illuminants and observers.
• The ISO 7724-2 standard defines a method for determining the colour coordinates of a paint film by comparison with a reference standard, using a spectrophotometer or colorimeter.
• The ISO 7724-3 standard provides a method for calculating colour differences between a paint sample and a reference, including acceptable colour variation tolerances.

These standards ensure that color measurements are consistent, repeatable, and comparable across instruments and laboratories, which is critical for quality control in industries where color accuracy is paramount.

ISO 7724 standards apply to paints, varnishes, and related coatings, including liquid paints, powder coatings, and cured films. They are used in:

• Automotive industry: Ensuring consistent color matching for vehicle body panels, upholstery, and trim, as seen in standards such as TPJLR.52.551 for detergent resistance.
• Architectural coatings: Verifying the colour homogeneity of paints used in buildings and ensuring aesthetic consistency between batches.
• Industrial production: Control of color quality in products such as household appliances, furniture and packaging.
• Quality control and research: Providing a standard framework for color specification in product development and testing processes.

These standards are particularly important for industries where color consistency impacts brand identity, customer satisfaction, and regulatory compliance.

ISO 7724 standards are critical for the following reasons:

• Colour consistency: Ensures consistent colour retention of paints and coatings across production batches, which is essential for brand identity and customer satisfaction.
• Quality control: Provides a standard method for verifying that coatings meet color specifications, reducing defects and rework costs.
• Global standardization: Facilitates international trade by enabling manufacturers and suppliers worldwide to communicate their color requirements using a common framework.
• Compliance with various regulations: Supports compliance with industry standards such as automotive coatings (e.g., TPJLR.52.551 standard) or architectural paints where color accuracy is regulated.
• Aesthetic durability: Ensures that coatings are resistant to color changes caused by environmental factors (e.g. UV exposure) when combined with standards such as ISO 2813 for gloss measurement.

As a result, ISO 7724 standards are a fundamental standard for the paint and varnish industry, providing a robust framework for measuring, specifying, and comparing the color of coatings. Its three parts support industries such as automotive, architecture, and manufacturing by ensuring that color measurements are accurate, repeatable, and aligned with global standards. By adhering to these standards, manufacturers can achieve consistent color quality, meet customer expectations, and comply with regulatory requirements.

Our organization, which has been operating for many years and meticulously follows global developments in science and technology, employs a skilled team and extensive infrastructure to conduct testing, measurement, and analysis in a wide range of areas for businesses across all sectors. In this context, we also provide testing services in accordance with ISO 7724 Paints and varnishes - Color measurement standards.