Yes, there is a difference in the ratios used for processing shallower
plates and thicker plates. Thanks for bringing it up. I don't believe
I've ever seen it mentioned before.
While it takes longer to ensure thorough photopolymerization on
thicker plates, thus longer exposure rates, the solubility range
difference is not as severe. While each job and each client have
different needs and expectations, my exposure range on shallower
plates is generally less than the washout time, whereas on thicker
plates my exposure range is generally much longer than the washout
time. By modifying the formula you can get to the floor on the thicker
plates without erosion occurring.
But I'm only talking about the process with platemaking machines here.
I don't know much about how you would be able to duplicate this with
I can think of a few of reasons for wanting to ensure this: You won't
end up with that unfinished look. In my case, I know I can't offer
plates that look unfinished to clients. Also, leaving material on the
floor denys relief depth (the reason for using thicker plates). As you
mentioned, without a clean floor, there is the ever-present danger of
> I do wash out by hand, but I think you could do what I'm talking
about with an automatic washout unit by just putting the plate in for
> What I have seen, through the loupe, with weak type elements, is
that often times the point or the line is there in the exposed plate,
but it gets undercut by the brush in the washout. It is as if the top
75% of the material got well-exposed and hardened, but the bottommost
25%, the foundation, did not. Maybe because the "hole" in the
negative is so small it has some effect on the halation?
> So, if you only wash away the top 75% of the unexposed material, and
leave the bottom 25% there, you leave the support for the finer stuff.
This may only be necessary if you are using the higher-relief
material (.060")- I haven't used the thinner stuff so I don't know if
it is prone to the undercutting problem. I imagine it may not be.
> I agree that exposure is the best way to ensure the fine stuff
stays. I only shorten the washout as a last resort, personally.
> Joel Benson
> Dependable Letterpress
> San Francisco