As the primary raw material for printing, the performance of paper directly determines the quality of printed ink colors. Only high‑quality paper can deliver superior color reproduction in printed materials. Therefore, a thorough understanding of the relationship between paper properties and print coloration, coupled with the judicious selection of paper tailored to the specific product and process requirements, is of great practical significance for enhancing product quality.

　　I. The Relationship Between Paper Smoothness and Color Appearance

　　Smoothness is a technical indicator used to assess the degree of surface irregularity in paper; it quantifies how flat, smooth, and uniform the paper’s surface is. Specifically, under defined vacuum conditions, it is measured by the time required for a fixed volume of air to flow between the surface of a paper sample—held at a specified pressure—and a smooth glass plate. The unit of measurement is seconds: the longer the time, the higher the paper’s smoothness. With better smoothness, the contact between the paper and the printing plate during printing is more even and complete, leading to more thorough transfer of the ink layer from the plate (for letterpress) or the blanket, and resulting in superior color reproduction. Conversely, paper with poor smoothness exhibits uneven and incomplete ink transfer, and its surface readily absorbs ink, yielding inferior color results—often causing mottling or fading in the printed output. Therefore, when printing fine‑detail work with finer screen rulings and smaller halftone dots, it is essential to use paper with high smoothness to ensure accurate reproduction of the original artwork.

　　II. The Relationship Between Paper Gloss and Color Appearance

　　Paper gloss refers to the degree of specular reflection on the paper’s surface, expressed as a percentage. The higher the gloss, the more effectively the surface reflects light like a mirror, enhancing the appearance and producing a bright, vivid finish. In practice, however, paper surfaces exhibit not only specular but also diffuse reflection, which can reduce overall gloss. Papers with high gloss tend to yield prints with richer, more vibrant ink colors and superior visual impact. In general, the smoother the paper, the higher its gloss, and the greater the glossiness of the printed image. There is a close relationship between paper gloss and smoothness, though gloss is not synonymous with smoothness; a glossy surface does not necessarily mean a perfectly smooth one. Given these characteristics, selecting the appropriate paper based on the nature of the print job is highly practical. For example, for publications where text predominates, papers with moderate gloss are preferable to minimize glare and reduce eye strain during prolonged reading. Conversely, for prints featuring predominantly graphic elements, papers with high gloss are recommended to achieve uniform, rich, and visually striking ink coverage.

　　III. The Relationship Between Paper Whiteness and Color Appearance

　　Paper whiteness refers to the paper’s ability to reflect light uniformly when illuminated; it is also known as paper brightness and is expressed as a percentage. The higher the whiteness, the more effectively the paper’s surface can accurately reproduce the color characteristics of the ink. This is because white paper reflects the colored light that has been subtractively synthesized through the transparent ink layer. Consequently, highly whited paper can reflect nearly all wavelengths of light, resulting in vivid, eye‑pleasing printed colors and excellent visual impact. By contrast, paper with low whiteness absorbs only part of the color spectrum, failing to faithfully render tonal contrasts and often leading to color shifts—such as yellowish, reddish, greenish, or bluish tints. When the paper itself exhibits a color cast, the resulting print color reflects the combined effect of both the ink and the paper, inevitably producing undesirable color deviations. In such cases, it is essential during printing to compare the paper’s whiteness and any color casts against the original artwork and to implement appropriate corrective measures. For instance, if the paper has a yellowish hue, it is advisable not to use inks with deep yellow, peacock blue, or bright red undertones; rather, one should select inks that complement the paper’s inherent color to minimize color shifts. Alternatively, color correction can be achieved through ink formulation techniques.

　　IV. The Relationship Between Paper Absorbency and Color Appearance

　　Paper absorbency refers to the paper’s ability to take up the vehicle and solvents in the ink, typically expressed as a percentage. Also known as ink absorption, it significantly influences the reproduction of color tone and the glossiness of the ink layer. Paper with high absorbency tends to produce prints with faded colors and a lack of gloss. Moreover, since most of the ink vehicle is absorbed by the paper fibers, the pigment particles are inadequately protected, resulting in an unstable ink film that can easily lead to “powdering” of the print. Conversely, if the paper exhibits insufficient absorbency, the ink layer will adhere poorly, drying will be slow, and the reverse side of the print may become smudged. Therefore, selecting paper with appropriate absorbency—based on the intended use of the printed material—is essential for ensuring consistent print quality. For example, newspaper printing calls for highly absorbent newsprint to meet the demands of high speed, urgent production, and cost-effectiveness. In contrast, when printing fine‑detail work requiring vivid colors, papers with low absorbency, such as coated art paper or glossy coated paper, are preferred. Among the paper properties that affect print color rendition, gloss and absorbency are the most critical. The combined effect of a paper’s absorbency and gloss on the final ink color appearance is referred to as the paper’s surface efficiency and can be calculated using the following formula:

　　PSE (%) = (100 - A (%) + G (%)) / 2

　　In the equation, PSE denotes paper surface efficiency; A represents the paper’s ink absorption capacity; and G stands for the paper’s gloss. Process testing demonstrates that, under identical processing conditions, higher paper surface efficiency yields maximum ink color strength while minimizing color shift and grayness. Research and testing of paper surface efficiency constitute a crucial step toward data‑driven, standardized printing processes, playing a vital role in effectively correcting color deviations and ensuring consistent print quality. Therefore, gaining a thorough understanding of how various paper properties influence the color reproduction of printed materials is undoubtedly beneficial.