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.纸张对颜色的影响

1. The influence of paper on color

光泽度与平滑度：印刷品的光泽度取决于纸张的光泽度与平滑度。印刷用纸的表面属于半光泽表面，尤其是涂料纸。

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，当光线以45°入射角照射到纸张表面时，约有4%的光会被反射掉，这就是首层表面反射光。而其余入射光穿过油墨层，经过油墨的选择性吸收后，再透过墨层反射出来，进入人眼，被人眼所感知，这就是我们观察到的颜色。若纸张的光泽度和平滑度较高，则首层表面反射光是做镜面反射，不易进入人眼，此时观察到的颜色基本就是透过墨层反射出的颜色。

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.撤淡剂对颜色的影响

2. The effect of diluent on color

撤淡剂是一种油膏状的无色透明物质，在专色印刷中主要起冲淡颜色的作用。撤淡剂的加入量不同，对色相的影响也不同，尤其是蓝色表现得明显。

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.

在配制专色墨的过程中，匀墨仪、展墨仪对油墨产生的剪切力、压力要比印刷机上的小。

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.

在画册印刷时不需加入撤淡剂，但在配墨制作色卡时只有加入撤淡剂，才能打出均匀的专色墨颜色展示卡。在色密度相同情况下，色卡与印刷品呈现出的颜色是存在色差的，这是因为撤淡剂的加入，改变了油墨中颜料的分布状态，使油墨对光的吸收、折射和反射都发生了变化，由此就产生了色差，这种色差是由系统的差异引起的。

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.

以上就是影响专色印刷色差的因素，另外刚印出的印品，油墨尚处于湿态，与干态时有一个密度差。湿色密度大于干色密度的现象称为干退密度现象。这是因为刚印出的墨层有一定的流平性，所以表面反射以镜面反射为主，看上去色彩鲜艳，光泽好。

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.