How Does Offset Printing Work

Offset printing is the most popular technique for commercial printing. It has been around since the 20th century, helping businesses produce stationery, leaflets, brochures, magazines, and cards in bulk. Also called offset lithography, commercial offset printing is also used for labelling packages such as boxes or cartons.

What is offset printing?

This printing technique is called ‘offset’ because it does not transfer ink directly onto paper like other printing methods do. Instead of going from plate to paper in two steps, ink is transferred first to a rubber cylinder and then printed on paper. The three-step offset method reduces wear and tear on the lithographic printing plate, thus prolonging its lifespan.

An offset printer includes three cylinders:

  • Plate cylinder
  • Offset blanket cylinder
  • Impression cylinder

In offset printing, the image area and the non-image area co-exist on the same flat surface.

Offset lithography works on the principle of oil and water separation. The plates have been treated to make image areas attract ink and non-image areas attract water to repel the ink. When water and ink are applied by the rollers to the plate, the oil-based ink sticks to the image while water sticking to the non-image area repels it.

Some offset printing presses use a silicone layer that repels ink instead of water. These systems are called ‘dry’ or ‘waterless’ offset presses.

4-colour printing

Offset printing presses use four basic ink colours: cyan (C), magenta (M), yellow (Y), and black (K). Each colour is applied separately, one plate per colour. Small dots of CMYK are pressed in specific patterns that form what looks like a wide range of colours.

Specialised offset printing can also use pre-mixed inks such as metallic and Pantone colours to create hues outside the standard printing colour range.

offset printing use four basic ink colours

How offset printing works

The first cylinder used in the offset printing process is the ‘plate’ cylinder. This thin cylinder has a plastic or aluminium plate around it. Each plate is customised according to the text and images to be printed onto the paper. The plate cylinder has been pre-treated to have the images attract ink and repel water. When the plate cylinder spins, it will make contact with rollers that apply the ink and water.

The second cylinder is the ‘offset blanket’ cylinder. This cylinder has a rubber blanket around it and turns in the opposite direction to the plate cylinder. When both cylinders roll against each other, water is squeezed away and ink is transferred onto the rubber blanket. This creates a mirror image of the ink design.

The third cylinder in the offset lithography process is the ‘impression’ cylinder. Made of clean steel, it turns in the opposite direction to the blanket cylinder. The impression cylinder transfers the ink as it presses paper against the rubber blanket.

Offset printing presses are fast and efficient – they can print up to 18,000 sheets per hour. With each sheet containing up to 48 pages of A4 or letter-sized content. A typical offset press can print eight pages in one sheet – which translates to around 120,000 pages per hour!

offset printing presses are fast and efficient

Sheet fed vs. web offset

Sheet-fed offset printing presses run individual sheets in various sizes. A full-size sheet measures around 1 metre by .75 metres, with half and quarter size varieties.

Web-offset printing presses, on the other hand, are fed by a large roll of paper. This “web” goes through the press in a continuous length.

Sheet-fed presses are practical for printing marketing materials. Web presses are more cost-effective if you are printing catalogues, magazines, and newspaper inserts in quantities of over 50,000.

How to start an offset printing run

Before starting a new print run, the printing plates must be replaced and a number of pages are printed to check if the quality is optimal. This is called the “make ready” time, which can last up to 15 minutes depending on the complexity of the printing job. If you are printing on a single-colour press, you must completely clean the ink system first before printing another colour.

To start the “make ready” process, the imaged plates are clamped onto the plate cylinders and the settings are adjusted for ink density. An initial batch of sheets is printed at a low speed and the colour registration as well as the ink/water balance are inspected.

the more your print, the less you pay

Offset printing vs. digital printing

While offset printing produces great-looking prints at minimal cost, some projects do not require volume runs in the thousands. If your project is less than 500 pages, then the best solution is digital printing.

Advantages of digital printing:

  • Ideal for small printing jobs (1 to 500 pages)
  • Easy to tweak colours
  • Variable data capability (names, addresses, or numbers on a card can be changed easily)
  • No initial cost of creating plates
  • Quick turnaround
  • Eco-friendly

Advantages of offset printing:

  • Most cost-effective method for large printing jobs
  • The more you print, the cheaper the price per page
  • Can accommodate a wide variety of paper types with custom finishes
  • Metallic, fluorescent, and other custom inks available
  • Highest possible print quality with accurate detail and colour fidelity

In commercial offset printing, the more you print, the less you pay. After the initial cost during setup, you will only spend a few cents per sheet for the paper and ink. If you need to print flyers, brochures, booklets, newsletters, and other materials in large volumes, the office printer or even a professional digital printer is not the way to go. They are less efficient and more costly.

If you need to print a large batch quick, then offset printing can make it happen. Once the initial design has been transferred to the plate cylinder, printing onto paper only takes a matter of seconds.

Offset printing produces sharp typefaces, fine details, and images with rich, accurate colours. An ordinary printer won’t be able to match this high level of quality.

Let Jennings help boost your print marketing strategy

If you need high-quality booklets, brochures, catalogues, flyers, business cards, corporate stationery, or other promotional materials, choose a commercial printer with 45 years of experience. Jennings Print is a family-owned printing house specialising in offset printing. Located in the heart of Newcastle, we also provide graphic design, colour reproduction, and branding services.