Printing, as a kind of image and character reproduction technology, its social significance lies in that it records and spreads the corresponding history and culture while reproducing words and images. Therefore, the country where printing technology appears must be the ancient country of human civilization. As a practical technology for reproduction, printing was invented by the Chinese people, and the well-known seal is its early prototype. What factors affect the color difference of spot color printing? Let's talk about it today.

1.紙張對顏色的影響

1. The influence of paper on color

光澤度與平滑度：印刷品的光澤度取決于紙張的光澤度與平滑度。印刷用紙的表面屬于半光澤表面，尤其是涂料紙。

Glossiness and smoothness: the glossiness of printed matter depends on the glossiness and smoothness of paper. The surface of printing paper belongs to semi gloss surface, especially coated paper.

在彩色印刷品上，當光線以45°入射角照射到紙張表面時，約有4%的光會被反射掉，這就是首層表面反射光。而其余入射光穿過油墨層，經過油墨的選擇性吸收后，再透過墨層反射出來，進入人眼，被人眼所感知，這就是我們觀察到的顏色。若紙張的光澤度和平滑度較高，則首層表面反射光是做鏡面反射，不易進入人眼，此時觀察到的顏色基本就是透過墨層反射出的顏色。

On color printed matter, when the light rays irradiate the paper surface at an incidence angle of 45 degrees, about 4% of the light will be reflected, which is the reflected light from the first layer surface. And the rest of the incident light through the ink layer, after the selective absorption of the ink, and then through the ink layer reflection, into the human eye, perceived by the human eye, this is the color we observed. If the glossiness and smoothness of the paper is high, the light reflected from the surface of the first layer is specular reflection, which is not easy to enter the human eye. At this time, the color observed is basically the color reflected through the ink layer.

2.撤淡劑對顏色的影響

2. The effect of diluent on color

撤淡劑是一種油膏狀的無色透明物質，在專色印刷中主要起沖淡顏色的作用。撤淡劑的加入量不同，對色相的影響也不同，尤其是藍色表現得明顯。

Diluent is a kind of colorless transparent substance in the form of oil paste, which mainly plays the role of diluting color in spot color printing. The effect of diluent on hue is different, especially blue.

在配制專色墨的過程中，勻墨儀、展墨儀對油墨產生的剪切力、壓力要比印刷機上的小。

In the process of preparing spot color ink, the shearing force and pressure produced by homogenizer and spreader are smaller than those on the printing press.

在畫冊印刷時不需加入撤淡劑，但在配墨制作色卡時只有加入撤淡劑，才能打出均勻的專色墨顏色展示卡。在色密度相同情況下，色卡與印刷品呈現出的顏色是存在色差的，這是因為撤淡劑的加入，改變了油墨中顏料的分布狀態，使油墨對光的吸收、折射和反射都發生了變化，由此就產生了色差，這種色差是由系統的差異引起的。

There is no need to add diluting agent in album printing, but only adding diluting agent in matching ink to make color card can produce uniform spot color ink display card. In the case of the same color density, there is a color difference between the color card and the printed matter. This is because the addition of diluent changes the distribution of pigment in the ink, and changes the absorption, refraction and reflection of light in the ink, resulting in the color difference, which is caused by the difference of the system.

以上就是影響專色印刷色差的因素，另外剛印出的印品，油墨尚處于濕態，與干態時有一個密度差。濕色密度大于干色密度的現象稱為干退密度現象。這是因為剛印出的墨層有一定的流平性，所以表面反射以鏡面反射為主，看上去色彩鮮艷，光澤好。

The above factors affect spot color printing color difference, in addition, just printed, ink is still in wet state, and dry state when there is a density difference. The phenomenon that wet color density is greater than dry color density is called dry density phenomenon. This is because the newly printed ink layer has a certain leveling, so the surface reflection is mainly specular reflection, which looks bright and glossy.