What is Digital Printing?
In the family of print processes digital printing is the baby of the bunch at just 24 years of age. The name is derived from its set up process as the image which is required to be printed is taken directly from a digital source, namely a computer file. This method is the go to option for short run, quick turn around projects, as compared to alternative printing methods – such as screen and lithographic, the set up process, in terms of time consumption, is minimal.
The method is most commonly utilised alongside inkjet and laser printing techniques where the ink is deposited directly from the printer head onto the substrate (surface to be printed) one spot colour at a time. The product is then dried using a UV curing process.
What is Screen Printing?
The ancestry of print culture arguable owes itself to screen printing. Believed to have links to ancient Egypt and heritage in the Song Dynasty of 11th century China, the process, as we know it today, was refined in early 20th century England by Samuel Simon; who in 1907 was granted a patent for utilising silk as a screen for printing. The process would go through further innovations, over the next 50 years, with printers experimenting with the use of different chemicals which in turn lead to the inception of photo reactive stencils. The creative history of the process would continue into the 1960s with Andy Warhol unveiling his screen printed depiction of Marilyn Monroe, taking the process from private galleries and into the public eye. With such exposure it was just 5 years later that a patent was applied for, for a commercial screen printing machine, by inventor Michael Vasilantone which was used to print slogans and basic graphics on t shirts. The psychedelic 60’s is hailed as the epoch which gave birth to youth culture in the western world, and I believe that the ideologies and iconography of the era are deeply routed within the screen printing process, so next time you don your favourite t shirt or ponder a Andy Warhol print take a second to consider the long and arduous journey the process has taken to help define contemporary culture.
Screen printing is incredibly versatile as it can print to any substrate, regardless of shape, thickness or size. It can also apply a greater thickness of ink than other print processes, this means it is incredible successful for printing block colour, as there is no risk of banding. The method encompasses 3 elements; the screen, the squeegee and the ink. The screen is made by stretching a porous mesh over a frame, typically made of wood or metal. A stencil of the image to be printed is then produced on the screen; this can be done either manually or photo-chemically. If the design includes more than 1 colour then a separate screen is to be made to coincide with the placement of each individual colour. Once the screens are prepared the printing process can begin. The print process comprises of placing the screen over the substrate, the ink is then placed on top of the screen. Once this has been done the ink is forced through the screen by the squeegee, as the ink will only pass through areas where there is no stencil a replica image is produced on the substrate. The ink is then dried using a UV curing process with the process being repeated until the number of colours required for the design have been fulfilled.
What is Lithographic Printing?
Have you seen what happens if you give your frying pan a wash after making a bacon butty? Well firstly you’ll get a scolding from your wife/mother/brother/lover for attempting to pour fat down the plug hole, failing that you may also notice that the oil you’ve used will float separately from the water. And this ladies, gentleman, bacon butty lovers the world over, is the original principle of lithographic printing; the non miscibility of water and oil.
The technique was developed over 200 years ago (1796) by German playwright Johann Alois Senefelder. He was making little money from his plays, without the ability to sell of copies of his works, so in an act of self preservation he began to experiment with reverse imaging (the act of preparing an image for print by making a reverse copy of it) on cheap limestone.
His choice of material was namely down to the difficultly, and expense, of creating copper plates, which were the standard material for printing at the time.
Another innovation Senefelder birthed during this time was the ability to amend copper printing plates by using a liquid mixture of wax, soap, lamp black and rain water to add to or alter the image already inscribed.
Due to Senefelder’s intrepid nature it was not long until he began using his home made correction fluid in conjunction with the limestone slabs, doing so allowed a realisation that he could paint an image on the limestone which was resistant to water. Through further experimentation he then realised that if he was to treat the limestone with water, and then with oil based ink, he could create an image where the non printable areas would repel the oil based ink. When the slab was then applied to paper the image would be duplicated the right side up.
Senefelder named the process “chemical printing”, with the patent being approved in 1799, 3 years after his original printing trials. This technique is the linchpin of lithographic printing as we know it today.
As you can imagine the process has developed somewhat over the centuries and is no longer produced by disenfranchised playwrights rubbing lamp black on old bits of limestone.
In a contemporary print house materials such as aluminium, polyester, mylar or paper are used to create the printing plates which are then covered with photosensitive emulsion. A photographic negative of the image to be printed is placed on top of the plate and then exposed to ultraviolet light, the emulsion that remains after this process creates a positive image of the photographic negative.
The plate is then affixed within the printing press, having water and hydrophobic ink applied to allow the image to be printed, not too dissimilar from Senefelder’s original process. Before applying the ink to the substrate the plate rolls against a rubber cylinder in order to get rid of any excess water, the cylinder also picks up the ink from the plate and then transfers it to the desired substrate by it being passed between the rubber “blanket” cylinder and an “impression” cylinder – this part of the process is what the description “offset” is referencing.