The artwork to be printed goes directly from a computer as an electronic file, with no film or plate needed, to a digital press.
Litho or digital print are the choices for most commercial print jobs. Both have their strengths and cost implications.
For personal stationery and invitations Impact offers thermography through its subsidiary Saint Owen's Press.
Lithography derives from 'writing with stone' from the days when a stone was etched and used as a printing plate.
Working on the principle that oil and water repel one another litho printing today uses a metal printing plate that accepts ink only to those areas to be printed, water filling the gaps.
As the Plate cylinder is rotated - see diagram - ink is transferred from the reservoir, then transferred again to the Blanket cylinder, and then to the printed page by pressing between the Blanket and Impression cylinder.
Litho printing produces a sharp image because the rubber covered Blanket conforms to the small surface variations of paper.
If a page was to be printed directly from the plate cylinder the image will be reversed. The offset process of using the Blanket cylinder corrects that, hence litho offset.
Digital or 'on demand' printing is similar to using a desktop printer. Writing, designing and pre-press are all part of the digital workflow. Files go electronically to a printing machine. No film or plates are involved.
Typically short run documents from text books to promotional flyers and inserts are the candidates for digital printing.
The process offers speed, flexibility and the opportunity for considerable personalisation and variation within a print run.
Also known as raised printing, thermography begins with offset printing using ink that dries slowly.
Printed sheets leave the litho press by a conveyor belt. The sheets are then sprayed with with a fine resin powder which sticks to the wet ink. A vacuum unit collects loose resin from non inked areas and finally, the sheets pass through a heating unit that melts and swells the resin on the inked areas, raising the printing above the surface of the paper.
Thermography costs less than engraving and to the untrained eye looks and feels similar.
Litho offset and digital printing come with their own advantages and quality and cost implications.
Pros
Best for most jobs.
Accurate pre-press proofs.
High quality finish.
A wide range of paper choices and special inks.
Low unit cost for long runs.
Cons
High start up costs of making a film or plate.
High unit costs for short runs.
Slow and expensive turnaround compared to digital print.
Pros
Fast turnaround.
No film or plate.
Print only the number you need.
High degree of personalisation.
Easy adjustment during print run.
Cons
Higher unit costs for long runs.
Less accurate pre-press proofs.
Less accurate colour matches.
Reduced paper choices and no special inks.