The rule of inking on the gravure printing machine can be understood in four sentences!

1. The depth of the engraved characters and patterns on the plate cylinder directly affects the amount of ink transferred to the printed material. If the design is deeply etched, more ink is required to ensure full coverage. Conversely, if the pattern is shallow, less ink is needed to avoid over-inking and potential smudging.

2. The material hardness of the impression cylinder and the pressure applied during printing also influence the ink volume. A softer impression cylinder tends to transfer more ink due to its ability to conform better to the surface, while a harder cylinder may result in less ink being picked up. Similarly, higher pressure increases ink transfer, whereas lower pressure reduces it. This makes both material choice and pressure settings critical for consistent print quality.

3. Ink viscosity plays a major role in determining how much ink is applied. Higher viscosity inks tend to be thicker and may not flow as easily, leading to a heavier ink laydown. Lower viscosity inks are thinner and spread more readily, resulting in a lighter coverage. Balancing this factor is essential for achieving the desired print outcome without excessive ink buildup or insufficient coverage.

4. The speed at which the printing process occurs also impacts the ink amount. Faster speeds often require thinner inks to prevent issues like streaking or uneven distribution. Slower speeds allow for slightly thicker inks, which can help maintain even coverage and reduce problems like water marks or drying issues.

Among all these factors, the plate cylinder is the primary determinant of ink volume, while ink viscosity is considered the most influential variable. Viscosity and ink thickness are closely related, though not exactly the same. When measured using tools like a paint cup or Zahn cup, they are often treated as equivalent for practical purposes. In everyday terms, high viscosity is referred to as "thick" and low viscosity as "thin."

Understanding these relationships helps in adjusting ink properties based on the printing conditions. For example, when the plate has deep engraving, a thicker ink is needed to fill the cells properly and avoid ghosting—where an image appears faintly around the edges. On the other hand, shallow engravings require thinner ink to prevent the ink from clogging the plate and causing blockage. Similarly, fast printing speeds call for thinner inks to prevent issues like unclean scraping, while slower speeds benefit from slightly thicker inks to avoid water marks or ink running.

Common problems such as knife lines, ink starvation, fake drying, and ink bleeding are often linked to ink that is too thick. Therefore, careful management of ink viscosity is crucial for smooth and high-quality printing. To summarize, here are four simple guidelines:

- Deep engraved patterns require thick ink;

- Light engraved patterns require thin ink;

- Fast printing speeds require thin ink;

- Slow printing speeds require thick ink.