Chapter 2
Preparing Art for Screenprinting
The Originals
The original 'art' or design' to be printed can come in many forms, but
must eventually be converted to a stencil image on the screen. In screen
printing, only one colour can be printed at one time, and so multi-coloured
print jobs require a separate piece of film to create each colour's stencil
when working with photostencils. When we talk about art for screen printing,
we really mean 3 different things:
1. The
Original Art or Design
This can be in the form of a sketch, a layout on a computer, a painting
or drawing, a typewritten rough, or a finished camera-ready design. ¨
>From this original you can determine what you are going to print, the
size, location on the substrate, and number of colours required to reproduce
the image. ¨ Decide at this point if the art is reproducible or usable
for screen printing. Some images just won't work, or become too expensive
or difficult to reproduce. A good screenprinter should develop the skills
to identify problem prints when they first see the job, not after they
tried printing it. ¨ Remember, most clients won't know the difference
between many print processes, and may not understand why that multi-coloured
logo their kid designed using crayons or a low-end graphics program will
be impossible to colour separate without a big outlay of cash. Be gentle,
but don't be afraid to say no. The best designers and artists know the
criteria for the particular media, and design accordingly, not the other
way around.
2. Mechanical
Art
This is an interim art step where the elements of the design are composed
or laid out with proper type, artwork is changed to camera ready images,
or, in the case of continuous tone or full colour originals, scanned as
digital information in a computer. At the end of this stage, all design
elements are in place relative to each other, colours have been separated
to individual overlays or plates, in register, and trapping considerations
where colours meet have been built in. The term 'camera ready' is used
to describe the art at the end of this step. With the mass conversion
to computers for graphic prep, some of this type of terminology will find
itself up on the shelf, along with 'paste-up', 'silkscreen', and 'typesetter'.
¨ The term 'mechanical art' refers to the physical re-scaling and building
of the separate colour plates, with type and halftoned photos. In the
old days of paste-up and camera shots, this was done as separate steps,
and then laid out on a board with overlays, ready for the darkroom.
3. Film
Positive
A film positive carries an opaque image on a transparent film, which is
identical to the image to be printed. This film is used to expose a stencil.
(Artprinters take note: I'm not ignoring the ability to draw directly
on the screen with resist, rip paper and stick it under the screen, cut
water soluble handcut stencils, or use other methods to make screenprinting
stencils as a way of creating unique screenprinted works of art. But that's
a sign that you probably want to stay 'improvisational' . There's more
on this in the 'Screens and Stencils', but not a lot. Sorry.)
Let's
Look at Each Step in More Detail….
Original Art or Design
Line drawings (or line art, which is art or type with no tonal shading)
should be in black on white, irregardless of the final colour. Photos
or works of art need to be scanned (digitalized) to prepare them for conversion
to halftone art, or separation for printing process colour. Alternatively,
you can use a process camera and convert the images using halftone filters.
This is how they used to do it, and it is a disappearing skill. Although
process cameras can match a scan for quality, and win hands down for price,
digital film production is becoming more popular because designers can
transfer art files directly, change elements quickly, and processing chemicals
inherent in photo-based film are eliminated. Nearly all modern graphics
prepress equipment and training is centred around digital technology.
Note: To reproduce tonal variations in most types of printing, it is neccessary to convert the greyscales of continuous tone photos to a screen of small dots, which fool the eye into thinking it sees a grey area even though the print colour is black. They use these dots to print multi-colour as well. This is called 'four colour process' or 'CYMK' if you were raised by a computer. Look at the colour funnies, and then look at a magazine photo with a magnifying glass. Depending on the tonal value of an area, the dots are smaller or larger, or more concentrated. One of the major drawbacks to screen printing compared to other printing methods is its physical limitations in the reproduction of fine halftone dots.
Typesetting and layout is now easily done on a computer, either in the shop, in the home, or by a designer. If you are an artist and directly creating a screenprinted fine art piece, hand painting, inking, and hand-cutting can be done directly on clear mylar, acetate, or rubylith, skipping the mechanical art stage. Even if you are working this way, you will probably want to draw a sketch at size to figure out elements of the design.
Mechanical
Art
The computer has now overtaken the drafting or layout table as the workstation
of choice in screen shops. Most PC's and all Mac's have graphic and layout
capabilities, so that designs can be completely laid out, corrected, proofed,
and OK'd before producing final film. Programs such as Corel Draw, Adobe
Illustrator, Pagemaker, Photoshop, etc. allow all the old functions of
typesetting, enlargement and reduction using a process camera, paste-up,
masking, and producing overlays to be done by one person at one computer
workstation.
Keep in mind, there is still a place for some traditional methods, even in the most modern art department. Large flat areas of colour are still more economically produced using knifecut rubylith film. The need for this type of overlay is determined at the mechanical stage, but cut using the final film as the layout guide. All work should be thoroughly proofed at this stage before producing final film. At the end of this step run a quality control check for: Spelling, missing components, registry of multicolour plates to each other, trapping and colour printing order.
Film Positives
Remember, the image on the film will be the image on the stencil, which
will be the final printed image! Mistakes don't disappear in screen printing,
they get magnified. ¨ Make sure the film you are using has enough density
of black. Just because it looks black doesn't mean it will block light.
¨ Positive images are used in making screenprinting stencils. Negatives
are used in offset platemaking. Make sure you specify a film positive
when ordering film from a reprographics or design firm. Film positives
can be made using the following methods:
- Litho film, which is the traditional way of producing large format film. Lith film is shot in a process camera and produces a negative of whatever is shot, as line art. (no grey) Usually a smaller negative is produced from an original layout, and then a 'blow-back' or enlargement is shot from the negative, which becomes a positive. (positive art >internegative >positive film) The film is processed in a developer and stop bath. It is inexpensive, but must be processed in a darkroom using chemicals.
- PMT or stat camera, where the image is shot on a paper throw-away negative and transferred to a special treated film by running both materials through a developer bath and a set of rollers. This system was quicker and simpler when introduced in the 1960's, and replaced litho film in design and print shops when smaller format (up to 18" x24") film was required. Most shops have switched to computer technology and both the above systems (using cameras) have declined in use over the last 5 -10 years.
- Linotronic, or digital film. Usually output by a specialized colour sep company, or a film output service, or in-house in larger screen and offset shops. This film is produced from digital images created on computer programs and modemed or supplied to the output device on disc. The output devices are expensive, but produce very accurate and dense film, and are integrated with high end laser scanners to do high quality process and halftone work. This type of film is now industry standard.
- Laser printer using specially treated mylar. Very popular with small shops using computers for layout. Inexpensive and fast, but not super high quality. As long as the laser printer is good and has high resolution, this system is probably acceptable for 90% of average screen jobs, as long as the size isn't an issue.
- Inked by hand on mylar or acetate, or knife or computer cut on rubylith. Only suitable for specific applications or flat colour areas. For the fine artist, this method allows the use of familiar tools (rapidograph style tech pens, conte or litho crayons, certain pencils or markers, brushes, etc.) to be used to create a drawing that can then be exposed directly, without secondary processing.
- Thermal or inkjet digital printers. Cheaper than high-end linotronic, with quality that is not noticeably different, many shops are switching to this as affordable inhouse film production technology. These types of printers are available in wider and wider formats every year, and can be driven with regular computers and minimal software outlay.
Tips &
Tidbits
When ordering any film for screen printing, specify 'right reading emulsion
up film positive'. ¨ When ordering large blowups from smaller mechanical
layouts, it is neccessary to communicate the final size to the camera
operator. This is communicated as a percentage. An easy way to determine
exact enlargement or reduction percentages is to measure the width or
the height of the original and the width or height of the final desired
size, then divide to find the desired percentage.
Here's how: Original width 9.5 inches. Desired width 12 inches. Divide 9.5 into 12 to determine the enlargement percentage. (1.26 = 126%) Divide 12 into 9.5 to determine a reduction percentage (.79 = 79%) Ø This works when you know any two dimensions from the original and the finished size. The percentage can be multiplied by any other known measurement on an image to determine corresponding size on a finished piece. Ø 100% is the same size, less than 100% is a reduction, and more than 100% is an enlargement.
Film is very delicate, and should be handled with care and kept clean at all times. ¨ Film should be examined carefully before use for flaws, scratches, misalignment or mis-register, and corrected either with opaque touch?up, or by reshooting. Films for screenprinting can be stripped together with other pieces of film using clear tape to make larger images, or add elements to existing film.
Opaquing pens, available from a graphic supply shop, are really handy. Blockout 'tuche' can be applied by brush, and is water soluble so it can easily be removed.
A Note
About Graphic Supplies:
I don't want to start any arguments, but it has been my observation over
the years that many of the best materials are available from commercial
graphic suppliers or screenprint supply houses. Screenprinting materials
available from fine art stores tend to be hobby grade, limited in selection,
and don't do a good job past a certain point. If you are serious about
what you are doing - and hey, you've read this far- always seek out the
best materials you can afford, coupled with good advice.
New technology
in the Screen Art Department
Computers The only way to fly. One skilled operator with around $5,000
worth of hardware and software can deliver 90% of an average screen shop's
art needs in less time and for less money than was ever imagined even
10 years ago. Goodbye cameras, typesetters, paste-up, and stripping. Hello
hard drive crashes, corrupt files, and yearly equipment upgrades.
Direct Projection Small scale negatives are enlarged and projected directly on the coated screen. Eliminates costly full-size film, vacuum frame for exposure, and a few traditional steps in the process. Digital Ink Jet and Thermal Imaging Positives Print full size positives directly from computer, using an opaque ink jet plotter on a transparent film media. Advantage is no developing chemicals, no darkroom, and it's affordable enough for small operations because it runs on existing graphic computer programs.
Digital Ink Jet Direct to Screen Prints image with water soluble opaque ink directly from the graphic files to the coated screen. Eliminates the need for film positives, vacuum frame for exposure, and even more traditional steps. This the equivalent to 'direct-to-plate' in offset printing.
Note from the Author: I hope you have enjoyed this month's chapter. If any readers have questions, comments or suggestions, please forward them to andynanc@mars.ark.com and I'll try and respond. Next month, come back to World Printmakers to read all about Screens and Stencils. In the meantime, keep your squeegee sharp…. Andy
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