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.

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.

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.