What is offset printing? How it works, and when to use it.

Offset printing: a simple definition

Offset printing is a printing method that transfers ink from a metal plate to a rubber blanket, and from the blanket onto paper or card. Because the plate never touches the paper directly, the image is “offset”, which gives the process its name. Its full name is offset lithography, and printers often just call it litho.

How offset printing works

Offset printing relies on one simple fact: oil and water do not mix. The plate is treated so that the image area holds oily ink and the blank area holds water, which keeps the ink off it.

1. The plates are made. Your artwork is split into four colours: cyan, magenta, yellow and black. Each colour gets its own aluminium plate, imaged by laser straight from the file.
2. The plate is dampened and inked. Water rollers wet the blank areas. Ink rollers follow, and the ink sticks only to the image.
3. The image is offset. The plate presses the inked image onto a rubber blanket. This is the “offset” in the name: the plate never touches the paper.
4. The blanket prints the sheet. The soft rubber presses the image onto the paper. Because it gives a little, it prints cleanly on textured stocks as well as smooth ones.
5. The colours build up. The sheet passes through one unit for each colour, and the four layers combine into the full-colour image.

Sheet-fed and web offset

There are two kinds of offset press. They work the same way and differ in how the paper goes in.

• Sheet-fed offset prints on individual sheets. It is used for brochures, booklets, stationery and packaging, where quality and a choice of paper matter most.
• Web offset prints on a continuous roll of paper at very high speed. It is used for newspapers, magazines and catalogues printed in very large numbers.

Both are forms of commercial offset printing: the large presses run by print companies for business, publishing and packaging work.

Advantages and disadvantages of offset printing

Advantages

• Low cost per copy on long runs. Once the plates are made, each extra copy costs very little.
• Consistent quality. The last copy looks the same as the first, even across tens of thousands.
• Exact colour. Spot inks such as Pantone colours can be printed to match a brand precisely.
• Prints on almost anything flat. The soft rubber blanket prints cleanly on smooth, textured and uncoated stocks.

Disadvantages

• Expensive for short runs. The plates and set-up cost the same whether you print 50 copies or 50,000.
• Slower to start. Making plates and setting up the press takes time before the first sheet is printed.
• No changes between copies. Every copy is identical, so names, codes or versions need digital printing.
• Changes cost more. A late correction means making a new plate.

Examples of offset printing

You will have handled offset printing today without knowing it. Typical examples include:

• Newspapers, magazines and paperback books
• Catalogues, brochures and annual reports printed in large numbers
• Cartons and product packaging
• Long runs of leaflets, letterheads and envelopes for large organisations

Offset or digital: how they compare

Which one should you choose?

For most business print, the choice comes down to how many you need and how soon.

• Choose digital for short runs, tight deadlines, or anything personalised. A few hundred flyers or a box of business cards is digital work.
• Choose offset for long runs where the cost of each copy matters, or when a brand colour has to match exactly.

There is no fixed number where one becomes cheaper than the other. It depends on the size, the paper and the number of colours, so ask for a price on both if your run is large.

You do not have to decide yourself. When litho is the right method for a job, we print it litho through our production partners, and we will tell you which way is better value before you order.

A short history

Offset printing began in England in 1875, when Robert Barclay used the method to print on tin. In 1904 the American printer Ira Washington Rubel found that passing the image through a rubber blanket gave a sharper print on paper, and offset printing on paper took off from there.

Presses fed from a roll, plates made by laser and computer-controlled inking followed over the next century. The principle has not changed.