Offset printing in depth: rubber blanket, printing plates, and ink balance
How the nature of the material determines the method
Offset printing is still the backbone of much graphic production—from books and magazines to packaging. The principle sounds simple: ink isn't transferred directly from printing plate to paper but through an intermediate station. In practice it requires a fine balance that the graphic technician must control.
§From printing plate to rubber cloth to paper
The name offset means precisely 'offset'. The image is exposed on a thin aluminium plate mounted on the machine's plate cylinder. From here the colour is transferred first to a rubber blanket — a rubber-coated cylinder — and only then to the paper. This gives a softer and more uniform colour impression than if the plate printed directly onto the paper.
- 01The plate cylinder carries the exposed printing plate with the image.
- 02The rubber blanket transfers the colour from plate to paper and is spared wear.
- 03The pressure cylinder presses the paper against the rubber blanket with the correct pressure.
§Damping water and color balance
Offset printing exploits the fact that oil and water repel each other. Non-printing areas of the plate are kept damp with fountain solution while printing areas absorb oil-based ink. The balance between ink and fountain solution is critical: too much fountain solution gives weak, washed-out colors; too little gives smudging where ink deposits where it shouldn't.
§Properties of print inks
Print inks should be selected based on the task, not just colour. Viscosity determines how easily the ink flows through the machine's ink system, while drying properties determine how quickly the paper can be further processed. Adhesion ensures the ink stays on the paper without smudging, and fastness tells you how lightfast or chemically resistant the ink is over time.
| Property | What it tells you |
|---|---|
| Viscosity | How viscous the paint is, and how it behaves in the paint mixer |
| Drying properties | How quickly the paint dries before the sheet can be post-treated |
| Adhesive ability | Whether the color binds properly to the paper or cardboard |
| Authenticity | How well the colour holds up against light, friction and chemicals over time |
§Paper and material play along
The paper and cardboard properties have a direct impact on how well the adhesive binds — wrong material can cause delamination.
§Inspection and adjustment along the way
Even a well-adjusted machine can drift over a long run. Therefore sample sheets are taken regularly compared with the approved proof sheet and both colour balance and moisture are adjusted if deviations occur. Standards such as ISO 12647-2 and PSO provide a common language for when a print is really 'approved' — not just by eye but according to measured colour values.
“Offset printing isn't just pushing a button—it's keeping a chemical and mechanical balance alive, sheet after sheet.”