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Methods for mixing paint colors in painting applications Abstract: This article introduces the methods used for mixing paint colors in painting applications, namely manual color mixing, computer-based color mixing, and fully automated computerized color mixing. It analyzes the advantages and disadvantages of each method, and outlines the basic principles that should be followed when using these methods, as well as the key factors that affect the accuracy of the resulting colors. Keywords: parent color; child color; manual color matching method; computerized color matching method; fully automated computerized color matching method 0 Introduction As people’s demands for paint colors become more diverse and personalized, along with the rapid development of the painting and repair industry, it is difficult for paint manufacturers or sellers to provide an adequate range of colors that can meet the needs of customers and repair workers in the market. It is often necessary to adjust the paint colors on-site, using standard color charts, sample colors, or actual samples as references. The so-called color mixing in coating application refers to the process of using two or more coatings of the same type but with different colors – namely the \"parent colors\" (the colors before mixing) – and mixing them in appropriate proportions until a new \"child color\" (the color after mixing) is obtained. This method is commonly used in the preparation of solvent-based coatings. Taking solvent-based coatings as an example, this article introduces the common methods for mixing coating colors in painting applications. 1 Paint mixing methods: Before the 1990s, for various reasons, the available paint colors in China’s paint market were mainly bright red, medium green, dark green, medium yellow, dark blue, medium blue, white, and black. Color mixing was often not necessary during application, and the only method of mixing used was manual mixing. By the early 1990s, with the development of the furniture and home renovation industries, and especially by the end of the 1990s, China’s automotive paint repair industry and electronic technology made rapid progress. Computers and electronic scales were utilized in the painting sector, which led to the emergence of \"computerized paint mixing\". At present, the fully automatic computerized allocation method has also appeared in our country and is being used on a small scale. 1.1 Manual color mixing method: The manual color mixing method is the simplest and most basic way of mixing colors. This method does not require specialized equipment, but it demands that the operator possess relevant color knowledge and certain operational skills. 1.1.1 Relevant color knowledge: Although there are many types of colors, and humans can distinguish nearly 300,000 different colors with their eyes, every color possesses three distinct characteristics, also known as the three attributes of color (or the three elements of color): hue (also called tone), brightness (also called lightness), and saturation (also called intensity). The hue and saturation of any color are determined by the combination of the three primary colors—red, yellow, and blue—while brightness is adjusted using black and white. As shown in Figure 1, equal amounts of red and yellow mixed together produce orange; equal amounts of yellow and blue mixed together produce green; equal amounts of blue and red mixed together produce purple. By adding a certain amount of white to red, yellow, and blue respectively, it is possible to create various shades such as pink, light red, light blue, light sky blue, light yellow, creamy yellow, egg yellow, and tooth yellow. Therefore, the manual color mixing method requires the aforementioned relevant color matching knowledge in order to be able to mix colors. 1.1.2 Confirmation of color: For any “sub-color” that is to be formulated, the standard paint color cards or sample colors, as well as the actual color sample, should first be placed in a well-lit area or under a standard light source, in order to identify the primary and secondary colors that make up that color. This helps determine which colors are used primarily to create the shade, what the approximate proportions are, and whether black or white is needed to adjust the brightness of the color. 1.1.3 Preparation before color mixing: Based on the confirmation of colors as mentioned above, prepare a certain quantity of various \"base color\" paints of the same type. Also, prepare all the tools needed for color mixing, as well as materials such as tin sheet or glass plate for creating samples. Clean all these tools to keep them in a clean state. 1.1.4 Sample preparation: Open the paint buckets of each color and stir them thoroughly using a mixing rod. First, take a few drops of the main color paint and drop them on the bucket lid, or on a tin sheet or glass plate. Then, in order of importance, add drops of the other colors using the same method. Compare with the sample colors and keep stirring as you add more paint, until the desired “sub-color” is achieved. It is possible to prepare multiple samples in this way. During the mixing process, it is necessary to confirm the ratio of amounts of each color, and pay attention to any issues such as clumping or uneven coloring. 1.1.5 Color mixing: Based on the proportions determined from samples, the approximate amounts of each \"base color\" paint are calculated. First, 50% of the main color paint is poured into the mixing bucket; then 50% of the required amount of each auxiliary color is added sequentially. After stirring thoroughly, a paint color sample is created. Once the solvent has evaporated and the color has stabilized, it is compared with the original color sample. Based on the degree of color difference, fine-tune the amount of each color added in the second round; pay special attention to the addition of dark-colored paints – add less and stir more to avoid excess. When the adjustment is close to the standard color, a new paint sample is prepared; once the solvent has evaporated and any floating color effects have stabilized, it is compared with the original color sample until the color matches closely. It should be noted that if the color sample is in a wet film state, a newly prepared coating can be dropped on the same surface for a wet-film comparison, resulting in complete consistency; if the color sample is in a dry film state, the color of the wet film obtained should be lighter rather than darker compared to the dry film sample. The color difference produced by this method is largely related to the operator’s skill. After multiple adjustments, the general color difference ΔE can be kept within 1.5 NBS (the color difference unit in the CIELAB colorimetric system). 1. 2 Computer-based color adjustment method: This is the commonly seen \"computerized color mixing\" in the market, named so because computers are used in the process of color mixing. In this allocation method, the computer actually acts as a large database of paint formulas, storing the standard formulas for various secondary colors provided by paint manufacturers; it also assigns codes (VIN) to each primary color and secondary color included in these formulas. Generally, different paint manufacturers have their own rules for coding paint colors, which correspond to a specific color chart. When formulating, first confirm or directly look up the code of the desired shade from the color chart with codes, then enter it into the computer; the computer monitor will display the formula for that desired shade. Then, based on the components and proportions specified in the formula, the amount of each primary color paint required is calculated; once the primary color paints with their respective codes are prepared, the mixing process can proceed. This mixing method is commonly used for repairing automotive topcoats. It generally requires equipment such as a computer, a digital scale, specific color charts, and various base paints of the same type with codes. The procedure for using this method is as follows. 1.2.1 Confirmation of the sub-color: If a sample color, an actual product color, or a standard color code is provided, it is first necessary to visually identify, within a specific set of coded color cards, the color card code that is closest in color to it. Then, the digital code of the color card that is most similar to the sample color, or even exactly identical to it, is identified; the color represented by this code is the sub-color to be formulated. If car repair paint is needed, the paint code for the topcoat can be found on certain parts of some cars. 1.2.2 Calculation of the amounts of various “sub-colors”: By entering the determined code into a computer, it is possible to see on the screen the composition of the sub-color paint represented by that code – namely, the various types of base paints and their quality ratios. By calculating based on their components and mass ratio, the amount of each primary paint to be used is determined. 1.2.3 Color mixing: Similar to the manual mixing method, after preparing the mixing tools, the various primary paints are mixed together manually one by one until well blended. For example, if the measured code for the locomotive’s topcoat is 201B2, entering this code into a computer will cause the display to show the formula for 201B2: 846 corresponds to 169.5 g; 522 corresponds to 1.3 g; 847 corresponds to 65.6 g; 556 corresponds to 80.7 g; and 325 corresponds to 154.6 g. Based on the above formula, the amounts of each primary color are calculated proportionally; the mass of each component is measured using an electronic scale, then these components are placed in a mixing container and mixed evenly either manually or mechanically. Thus, the preparation of the colored paint is complete. Compared with the manual color adjustment method, this method improves the accuracy of the initial mixing as well as the reproducibility of subsequent mixings, **reducing the number of times that mixing is required. Especially when the sample color is confirmed to be correct and the \"base color\" paint uses the paint code specified in the formula, the color difference ΔE can be kept at < 1NBS. 1. 3 Fully automatic computerized color matching method: This fully automatic approach consists of a computer-based color measurement system (including a spectrophotometer), a computer processing system (including color-matching software), and a computer-controlled color-assignment system (including measuring and actuating devices). Its color matching principle is roughly the same as that of computer-based color adjustment, but it differs in terms of identifying the \"sub-colors\", calculating the amounts of various \"sub-colors\" to be used, and adding them, with full automation being achieved. This method requires the use of fully automatic computerized color matching equipment, specialized computer color matching software (usually different paint manufacturers have their own such software), as well as various \"sub-color\" paints that are compatible with that computer color matching software. 1. 3.1 Confirmation of “sub-colors”: The confirmation of “sub-colors” in the fully automatic computerized color mixing method is carried out automatically by the computer-based color measurement system. To confirm a \"sub-color\", simply place the color measurement probe on the surface of the sample color; the data related to that color sample is then transmitted to the computer. Through analysis using color matching software on the computer, the composition and ratio of that color are displayed on the computer screen, thereby completing the confirmation of the \"sub-color\". 1.3.2 Calculation of the amounts of various “sub-colors”: Follow the instructions, enter parameters such as the desired quantity to be prepared, and the computer system will automatically calculate the amounts of each “sub-color”, displaying them on the computer screen. 1.3.3 Color mixing: Follow the instructions; the computer’s automatic color-mixing system will handle the addition and blending of various \"sub-colors\" automatically, after which mixing can be done either automatically or by hand. Furthermore, to reduce color differences, it can also be made into a color sample; once dried, the correction function of this computer color-matching software can be used to adjust the colors that were initially mixed. Based on the magnitude of the color difference, each “sub-color” can be automatically added again. Compared with the manual mixing method and the computerized mixing method, this method eliminates the interference of human factors and achieves full automation of the mixing process. Its color tuning accuracy is related to the precision of the system, but generally, after one adjustment, the color difference ΔE can be kept below 0.5 NBS. This technology is already well-developed abroad, with the price of each set of equipment being around 200,000 yuan; however, it is still in the developmental stage in China, and it is even less common in painting applications. 2 Conclusion No matter which of the three coloring methods is used, the same basic principles for matching colors applicable to paints of the same category must be followed when selecting colors. Since color science is an extremely complex discipline that is related not only to chemical composition but also to physical properties such as particle size, shape, and molecular orientation, color differences can exist between different manufacturers, or even between different batches of the same pigment from the same manufacturer. And these factors ultimately lead to color differences among paints of the same “base color”. Therefore, although computer-based color adjustment or fully automated computerized color adjustment methods offer higher accuracy and better reproducibility compared to manual color adjustment, when using these methods for the various \"parent colors\" within the same batch, it is possible to repeatedly generate multiple identical \"child colors\" at once. However, for different batches of each \"parent color,\" no matter which coloring method is used, even after multiple attempts at mixing, it is only possible to get colors that are similar to one another; it is not possible to obtain completely identical \"child colors.\" Therefore, in paint application, the accuracy of the various \"primary colors\" used for color mixing is key to ensuring the precision and reproducibility of the colors.