hisun.wong@citicorp.com
Date: 07/22/02-08:58:36 PM Z
Philippe,
I took the liberty of forwarding a message from Dave Willison on the
subject. Photogravure is a halftone process and the range of tone on
Polymer does not affect the printing. I am only speaking based on theory.
A lot of information in two attached e-mails.
Regards
Hisun
Hong Kong
-----Original Message-----
From: Dwillisart [mailto:Dwillisart@aol.com]
Sent: Thursday, January 17, 2002 10:22 PM
To: hisun.wong
Cc: Dwillisart
Subject: Re: photopolymer gravure and screenprinting
Hisun:
Both screenprinting and photopolymer gravure require a positive image
to create plates or screens. I usually start with a photograph that
has been scanned into the computer or a shot taken with a digital
camera. (I've even used three dimensional objects placed on the
scanner.) I then work with photoshop (image>adjust>levels)to alter
shadows and highlights to correspond to the type of process I'm using.
Many photopolymer plate and films, for example, require a positive with
shadow areas that are about 50 percent black. I use Photoshop LE, which
came with my scanner. (The full version of Photoshop has always been a
little expensive for my tastes!). With levels adjusted the image will
look somewhat light and flat. Remember, however, that the printing process
tends to darken the image and in some cases increase contrast. The bottom
line is that the positive image should not be judged with the same standards
that you would use to judge a good photograph.
When I complete the positive, I print the image using a laser printer and
laser transparencies. I bought a HP 1200 which produces a resolution ranging
from 600 to 1200 dpi. The HP 1200 prints up to 8.5 x 11, so any larger
images have to be printed on multiple transparencies. The image is printed
using a halftone dot pattern which is adjustable. I normally use the default
although the shape of the dot and the number of lines per inch can be changed.
(NOTE: Before I used the laser printer, I printed with an Epson 1160 inkjet
using standard paper. I then copied the image on to transparency film using
a small portable Xerox copier. Since inkjet printers do not produce a halftone
pattern, I used Photoshop or Painter filters to produce a halftone or mezzotint
pattern.)
After the positive is printed, it is transferred to a plate using a contact
frame and a UV light source. I use two types of plates: (1) Plexiglas with
ImagOn photopolymer film laminated via an etching press; (2) Andersen-Vreeland
precoated plates also known as "solar print" plates. ImagOn is less expensive
but the platemaking process involves more steps (the film must be adhered to
a plate). Also, I've found that Imagon is more prone to dust, scratches,
imperfections, etc. than the pre-coated plates. The downside to solar plates
is that the plate cannot be reclaimed (Imagon can be removed and the plate
reused). Also solar plate must be in perfect contact with your halftone or
the final print will show blank or light areas.
My UV setup is simple and inexpensive. For the Imagon plates I use two
500-watt halogen worklights suspended about 14 inches above the plate. My
average exposure time is about two minutes using a halftone laser positive.
For the solar plates, I use 4 black light bulbs (BLB) suspended about 6-8
inches above the plate. My average exposure time is about 3-5 minutes with
a laser halftone. Both plates are developed using a tray of water (for solar
plate) and water with soda ash (for Imagon). The plates are then re-exposed
to UV light for about 3-5 minutes to harden the plate.
I print both type of plates using an etching press and standard etching inks.
Ink is applied with matboard and wiped by hand. The plate is then run through
the press with a sheet of printmaking paper. I use arches 140lb hot press or
arches cover.
I hope this helps!
Dave Willison
-----Original Message-----
From: Dwillisart [mailto:Dwillisart@aol.com]
Sent: Saturday, January 19, 2002 10:21 PM
To: hisun.wong
Cc: Dwillisart
Subject: Re: RE: photopolymer gravure and screenprinting
Hi:
With a laser printer you don't need an aquatint screen. The laser produces
a halftone pattern of small dots that are visible if the print is viewed
close up. The pattern is similar to that used by photo magazines. The pattern,
however, is not the random or mezzotint pattern used in traditional
photogravure.
If you are looking for that type of image, you need to apply some type of
screen
or pattern to the digital image. This can be done in a number of programs
including Photoshop, painter, etc. It may also be possible to use an inkjet
printer (without a photoshop screen/pattern) since the inkjet produces a random
splatter of dots. The key is to produce an image with some type of pattern or
dot structure rather than a continuous tone. You can also purchase an aquatint
or halftone screen and use it in conjunction with an inkjet print
(transparency).
This involves a two-step process where the printing plate is exposed twice.
(First, to the inkjet transparency and second to the screen). If you don't want
to purchase a screen, you can also print a small one using Photoshop.
I don't use a particular curve that matches the plate material I use. I
generally
try to adjust a print using the "Adjust>Levels" controls in Photoshop LE. You
need
to adjust the image so that the shadow areas are actually a dark gray. The
easiest
way to accomplish this is to employ Adjust>Levels and monitor your progress
with
the Photoshop Info box open on your desktop. The info box provides a %K (black)
figure when the cursor is moved over the image, specifically the shadow area.
This figure should read about 50% for shadow areas and about 10% for the
lightest
areas with printable tone. Anything that reads at less that 10% will generally
print as white on the final etching.
I hope this helps.
Dave Willison
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