[PPLetterpress] Re: Exposure/washout units
I had thought, much like you do, that hand-washing would be accurate
than machine washing--until I recently switched over to a machine
washout. I purchased the machine for better exposure and for
convenience, but didn't anticipate better washout.
In fact, the machine washout produces noticeably better plates. The
main advantage to the machine is its evenness of pressure. You don't
need to check the plate periodically for unwashed areas because the
whole plate washes out at the same rate. Corners took notoriously
long to wash out by hand; now, I don't have to worry about overdoing
the washout in the center. This isn't such a problem on type, but a
10% or 5% screen in the middle of your plate will suffer from
excessive washout. Because its pressure is constant, it doesn't tend
to wash away isolated dots as easily.
Since the machine brushes are larger, they also get the plate out of
the water sooner. Some plates, especially the large (say, 11x17)
ones, had to remain underwater for 10+ minutes to wash out with a 4x8
brush. Leaving them underwater so long can cause delamination of the
plate. Oh, and the machine brushes don't have hard plastic corners
that can scratch the surface of your plate.
Handwashing works. Telling the difference between a machine washed
plate and a hand washed plate (by someone who has excellent
technique) would be impossible on most small plates. But for large
plates or ones with isolated dots, light screens, or very small text,
machine washing works much better.
- Thanks Gerald,
Your description of the washout machine action is about as I imagined, having
only seen one not in operation. My washout time is presently quite a bit
longer than others have mentioned, perhaps because I use a very soft brush
and only very gently agitate. Obviously still some room for experimentation
here, but my results now are quite consistent and it seems possible to
control it by hand washing.
My first question was probably simpler than your answer: just that the plate
references (such as MK or MLD) don't tell me much unless I am using the same
source for plates, I think. Would the MK152 be the same as the MS152 I get
from Gene Becker? Maybe I just need to go back to the various notes Gene gave
me to see if the answer is there. Similarly, I have had some difficulty
making comparison with materials supplied by NA Graphics, because the names
differ. So I thought it might help if I say Gene Becker's Miraclon MS152
rather than 152 or MS152....
Regarding toxicity, it sounds like it's a question of skin sensitivity rather
than poison or carcinogin. I have hand-washed maybe 40 sheets (A3 size,
297x420 mm = 11x15? cut to innumerable smaller plates) over six years or so.
No gloves. No noticable skin reaction, no other problems at all (except an
occasional cut from the sharp edge of the metal backing, of course). I do
keep the water running slightly (to keep the temperature constant) so maybe
the concentration is low. Or maybe I'm just not sensitive. So far, it seems
to me remarkably benign. The very slight odor from unexposed material also
seems inconsequential to me. UV light, of course, is bad for the eyes (and
skin as well, I think).
Best regards, Tom
Now It's Up To You Publications
157 S. Logan, Denver CO 80209
- Hello Tom,
The orbital washout unit has been the only way I have been able to produce
consistently good plates efficiently. The time factor is very important.
About twenty years ago, when the photo polymer was just entering the
market, I was told by salesmen that the plate could be exposed in the sun
and washed out in a sink with any brush. I spent what seemed and endless
amount of time discovering only that there are many variables. I built
things, converted things, nothing I did seemed to have the same results
twice, or that the plates were just not good enough. I like process, but I
was always off task trying to find a solution.
While not quite a glorious epiphany, the machine allowed me to make
accurate plates, in a short time with not so much guess work. I only had to
pay attention to the orientation and density of the negative, the suction
of the vacuum table, cleanliness of the kreene, monitor the wash out, water
temperature, drying and final exposure to harden the material. The process
is simple and consistent (generally).
I like to examine the plate during washout to check that as much
material has washed away as possible but not so much as to weaken its
structural integrity , (small bits of the design, or letters that break off
during printing that you don't notice until you are finished).
Gerald has a good explanation of the washout process.
I think Monotype had much more exacting details built into their
production, and while success at times seems atmospheric the documentation
they provided would allow you some success. There are just so many pieces
to pull together and each one requires complete attention to detail.
If you contact me off list I can send you some plate processing
instructions for Miraclon/Rigilon, this is the MLD made by Toyoba. They
also recommend it for crash printing, hot stamping and for pantograph
masters. I have only used it for letterpress printing.