Offset Lithography

Lithography was once considered an art, a specialised trade, today, it has declined to the point that most people would not know what it is.

Lithography – A 200 Year Old Profession

Lithography, derived from Ancient Greek lithos meaning ‘stone’, and graphein meaning ‘to write’, is a method of printing invented in 1796 by Alois Senefelder, a German author and actor. It was initially used for musical scores and maps but later became more widely used for printing text and images onto paper or other material.

The process of Lithography

200 Years ago, the image to be printed was drawn with a greasy substance onto the surface of a smooth and flat limestone plate which was then treated with weak acid and gum arabic (still used today) that made the un-greased parts of the stone more water attracting. The stone was then moistened and the water only adhered to the un-greased parts and finally, an oil-based ink was applied which stuck to the original image which was then transferred to a blank paper sheet producing a printed page.

Today, a similar process is followed but it is a lot more automated than it used to be and large machines are used for the process.

Modern Lithography & Printing as we know it today

Modern lithography uses the same process with more advanced technology and materials. The image is created as a polymer pattern coating that is applied to a flexible metal or plastic plate. Offset lithography – the process of printing that we use at Spectraprint – has replaced traditional lithography for medium to high volume printing since the 1960’s. Offset lithography uses metal plates in large printing machines that have rubber cylinders between the plate and paper. The ink is transferred from plate to paper with the rubber cylinders which helps keep the paper dry and allows high speed and fully automated operation.

Over the years, there have been many inventions and technical improvements in the printing process of lithography. Modern machines have multiple units and presses which allow for colour to be produced. This is called full colour printing or 4-colour printing which uses 4 different inks – Black, Cyan, Magenta & Yellow – that are put into different units of the machine, each unit has its own cylinders and presses for each colour. With computer technology, each colour has a corresponding plate which has a percentage of the image on it depending on the colour in the image. Once the paper goes through each unit, a full colour image is produced.

Before the machine operator gets started on the production of a printed sheet, the machine is thoroughly cleaned ensuring each unit is ready for the new job. During pre-production, also known as the make-ready process, the machine operator is able to adjust the strength of colour and positioning (also known as register) of each unit to fine-tune and create high quality, crisp colour images.

Offset Lithography vs Digital Printing

There are a few key differences between offset lithography and digital printing, which has become quite popular. The method of printing that you choose, depends on your specific requirements.

Digital Printing

Digital printing differs from offset lithography vastly. It is a completely digital form of printing, similar to your at-home printers that is connected to your computer, however, just much larger and capable of printing longer runs and bigger formats. Digital printing is only capable of printing in single colour or 4 colour. It is a more cost effective option for jobs that require smaller runs and jobs that may have multiple forms required such as printed wedding invitations. Different digital machines also have unique capabilities, such as being able to print on different substrates and weights, however, the downside is that you would have to find a digital printer that is able to print on the substrate you require.

Offset Lithography

The beauty of offset lithography is that it allows adjustment of colour and positioning to create the perfect printed product. Lithography can produce full colour prints and single colour prints depending on what is needed. Full colour prints can also be combined with specific tones and shades of colour, called spot colours, to further customise the print. This is necessary when a design has colour included in it that cannot be produced by traditional full colour printing such as metallic, neon or pastel colours.

The following table summarises the differences between offset lithography and digital printing as well as its pros and cons, however, please note this is not a complete list and these are general differences which may differ between the types of machines used.

Offset Lithography	Digital Printing
±10000 prints per hour	±2500 prints per hour
Make-ready set up	Minimal set up requirements
Time required for drying	Prints do not need to dry
Upfront costs, however minimum print run required for cost effectiveness as unit cost decreases as total quantity increases	Cost effective for low-volume or highly personalised jobs.
High volume generic prints	Can buy the quantities you need
Best quality prints	Quality has improved over the years due to advancements in technology
Paper stock usually between 60gsm & 400gsm	Paper stock usually between 70gsm & 300gsm
High level of colour accuracy as well as the ability to use metallic inks	Good at matching Pantones
Ability to print over a previously printed item	Cannot print over previously printed items
Capability of using prints for all types of finishing	Cannot use prints for certain types of finishing

Offset Lithography Pros & Cons

Pros	Cons
Various Sizes of printing (Business cards to large posters)	Expensive for small print runs
Customisable colours and strengths	Takes more time
Various weights and finishes of paper can be used	Not suitable for multiple designs of small runs
Cost effective for large quantities
Prints can have different finishes such as laminating, spot UV varnish etc.
Prints can be die-cut
Smoother finish and no pixelation

Digital Printing Pros & Cons:

Pros	Cons
Cost effective for custom designs and smaller quantities	Finishes on prints can be limited
Quick turnaround to produce finished format	Not suitable for heavier or textured substrates such as cardboard
Easily personalised	No protective coating, images are more likely to scuff
	Prints are more liable to crack when folded or creased
	Lamination may not adhere and cause bubbling

Ultimately, the method of printing you decide to go with depends on your unique requirements and the finishing you want to achieve.

If you want more information on our lithography expertise or if you would like an obligation free quotation for your print job, call us or click on this link to send us an email.