Definition
A standard colorimetric card is a physical tool for color comparison and evaluation through standardized color samples. It usually consists of a series of color blocks arranged in a specific order, each with a clear and stable color signature, corresponding to a specific numerical or grade identification. In laboratory testing and industrial quality control, standard colorimetric cards are used as a basic color reference standard for visual or instrument-assisted color determination, and their design and production must comply with relevant national or international standards.
Principle
Standard colorite cards work based on color matching and comparison. The human eye or photoelectric sensor determines which standard color patch is closest to the sample color by juxtaposing the color of the sample to be tested with the color block of a known color standard on the colorimetric card. Its theoretical basis involves colorimetry, which is the science of color, and the perception and description of color can usually be quantified by three stimuli or color space coordinates. Each color block on a standard color cuvette is precisely crafted and calibrated to ensure that its color values are within specified tolerances and have good batch consistency and long-term stability.
Measurement method
The methods of measurement using standard colorimetric cards are mainly divided into visual colorimetric method and instrument-assisted colorimetry. Visual colorimetry requires the operator to place the sample side by side with the colorimetric color block under a standard light source or specified natural light conditions, observe it at a specific angle, find the color block that best matches the color, and record its corresponding designation or grade. This method has clear requirements for the observer's color discrimination ability and lighting conditions. Instrument-assisted colorimetric method uses equipment such as colorimeters or spectrophotometers to measure and store the standard color data of each color block of the standard color card, and then measure the sample color, and objectively determine the closest match by calculating the distance ΔE between the sample color and the color of each standard color block in the color space. The calculation of chromatic aberration ΔE can refer to the CIELAB chromatic aberration formula: ΔEab = √((ΔL*)² + (Δa*)² + (Δb*)²)。
Influencing factors
The accuracy and repeatability of standard colorimetric card measurements are influenced by a variety of factors. Lighting conditions are the key factors, and the spectral power distribution, illuminance and observation angle of the light source must comply with the standard to avoid the phenomenon of homochromatic spectroscopy. The observer's visual characteristics, including normal color vision, fatigue level, and experience, can directly affect visual colorimetric results. The condition of the color card itself is also crucial, such as whether the color block is clean, whether there is physical wear, fading, or contamination, and whether it is used within the expiration date. The environmental background color and the juxtaposition of the sample with the color block can also interfere with the color contrast judgment.
Application:
Standard colorimetric cards are used in a wide range of fields for laboratory testing and quality control. In environmental monitoring, it can be used for water quality analysis, such as the determination of water color by platinum-cobalt colorimetry. In the food industry, it is used to evaluate the color grade of edible oils, juices, honey, and other products. In the chemical field, it is used to determine the color scale of chemical reagents or the color designation of products. In coatings, plastics, textiles and other industries, it is used for color quality control and incoming material inspection of raw materials and finished products. In addition, it is often used as a quick and convenient color evaluation tool in soil analysis, print inspection, and other fields.
Selection
Choosing the right standard color cuvette requires a combination of aspects. First, the specific criteria based on the test should be clarified, and the type, color range and grade division that meet the requirements of the standard should be selected. Secondly, according to the application scenario and accuracy requirements, decide whether to use a visual colorimetric card or require matching instruments for higher precision quantification. Furthermore, the durability of the colorimetric card, its colorfastness, and whether it provides a traceable calibration certificate are evaluated. For scenarios that require long-term monitoring, consider whether the supplier can ensure the consistency of product batches and subsequent replacement and supplementary services. Finally, whether the use environment, such as lighting conditions, is easy to meet the standard requirements should also be taken into account in the selection consideration.