Re: Sharpness, contone (was Re: Useful results from gum tests

Well Katharine, this particular Peter Marshall is actually saying that
nearly all of those still working in alt processes are now actually
printing gum using dots produced from ink jets which is a half tone, and
that this does actually work better than continuous tone. He might also
go on to say that continuous tone only works for gum as well as it does
because film has grain and is not true continuous tone.

And of course, he still says that your test simply shows - as we all
know - that laser printers with 600 dpi can't produce a decent halftone,
either theoretically or practically. But it makes no sense to expect a
better image out than you put in, which appears to be what you were
expecting in your test. Your test is, I'm afraid, entirely worthless in
this context. (Though as I said, it's quite a good way to get students
started, as it is almost impossible to mess up prints made in this way.)

A decent halftone needs a 16x16 grid to give 256 shades, giving 600/16 =
37.5 lpi for your laser - nowhere near enough for good results. You can
fudge this a bit with fancier algorithms, but not a great deal. Printing
at 1440 dpi it is possible to get decent results.

I'm not actually sure you can produce a true continuous tone through
photographic means, but I suppose using wet plate would approach this.
However I don't know of anyone making gum prints from wet plate.

Of course I simplify, and the irregularity of the paper surface will
also have a part to play. Hardening from the top down will mean
hardening down to the paper surface on the peaks but not on the troughs
of the image even with a more or less continuous tone image. But I think
there is no room for doubt that the process is easier with a suitable
halftone, although that may not necessarily mean better prints.

Regards

Peter Marshall
petermarshall@cix.co.uk +44 (0)1784 456474
31 Budebury Rd, STAINES, Middx, TW18 2AZ, UK
_________________________________________________________________
My London Diary http://mylondondiary.co.uk/
London's Industrial Heritage: http://petermarshallphotos.co.uk/
The Buildings of London etc: http://londonphotographs.co.uk/
and elsewhere......

Katharine Thayer wrote:
> John, what do you mean by "acceptably sharp"? Since sharpness is
> anathema to me (in fact I just spent $$$$$ on a soft focus portrait
> lens) it hurts me to have my work labeled "sharp."
> ;--)
>
> But, for the Peter Marshalls of the world who are still saying that
> gum doesn't print continuous tone well (another of those gum myths) I
> probably should have specified that that dead seagull negative that I
> use a lot for test prints, and that I used in the tests referred to
> here, is a continuous tone 4x5 negative.
>
> There's a page on my website that compares continuous tone to a
> stochastic dot for printing gum. It's not quite the same as halftone,
> which is what Peter was suggesting the other day would be the best
> kind of negative for gum, but it does address the more general
> question of whether dots are better for gum than continuous tone.
>
> http://www.pacifier.com/~kthayer/html/dotcont.html
>
> Katharine
>
>
> On Apr 11, 2006, at 8:34 AM, John Grocott wrote:
>
>> Katherine, May I say, but not as a gum printer, that I found your
>> three examples extremely impressive especially when I printed them on
>> glossy photo quality paper. The last one looks acceptably sharp
>> which you printed on paper, ''on a somewhat less- pigmented gum
>> emulsion''. I join with
>> ----- Original Message -----
>> From: "Katharine Thayer" <kthayer@pacifier.com>
>> To: "alt photo" <alt-photo-process-l@sask.usask.ca>
>> Sent: Monday, April 10, 2006 7:33 PM
>> Subject: Gum hardening: top down?
>>
>>
>> > Okay, I've coated a very thick, very heavily-pigmented gum
>> emulsion on
>> > mylar and printed it from the front and from the back. A couple of
>> > comments before I give you the URL:
>> >
>> > (1) though the emulsion was very heavily pigmented, two things
>> resulted
>> > in not a very deep DMax: (a) the fact that I used ivory black, a
>> > transparent pigment (if I were to do it again, I'd use lamp
>> black) and
>> > (b) the fact that it's printed on a transparent material and was
>> scanned
>> > as a transparency, with the light shining through it. But the
>> thing to
>> > note is, be that as it may, the DMax is about the same in both
>> prints.
>> >
>> > (2) there's a light brown pigment stain (ivory black is a brownish
>> black)
>> > in both prints that is probably a function of the heavy
>> pigmentation. It
>> > hardly shows in the prints themselves, but for some reason was
>> > accentuated in the scanning.
>> >
>> > (3) I don't honestly know what to make of the results. If you look
>> just
>> > at the prints on mylar, you'd have to conclude that back- printing
>> is much
>> > superior to front-printing, at least for a thick coat on mylar.
>> But if
>> > you compare the back-printed print on mylar to the regular
>> front-printed
>> > gum print (using a less heavily-pigmented emulsion) on paper (at the
>> > bottom of the page), it's hard to claim that the back-printed
>> print is
>> > superior. But since they are on different materials, it's apples and
>> > oranges.
>> >
>> > So I guess if I were forced to draw a conclusion from this rather
>> > inconclusive test, I'd say that if you are going to print on
>> mylar using
>> > a very thick and heavily pigmented emulsion, then you'll probably do
>> > better printing from the back. But if you're printing on paper,
>> you can
>> > get fine results printing from the front with a less pigmented
>> emulsion.
>> >
>> > http://www.pacifier.com/~kthayer/html/topdown.html
>> >
>> > Katharine
>>
>
>
Received on Wed Apr 12 14:33:36 2006