Mark,
What you say here not only makes sense, but in fact has been known
and understood and practiced by gum printers for a long time.
Amazingly enough, beautiful tricolor gums have been made for
decades, and even now people are starting out and making beautiful
tricolor gums without PDN.
Of course sensible gum printers would never try to print a negative
with DMax of 4.0 on gum; most people know that gum requires a less
dense negative. People have created those less dense negatives many
different ways, both in the darkroom and digitally. I'm lucky to
have a printer that prints a negative with all colors on
transparencies that is perfect for printing gum. Nor was excess
density a problem with the laser printer negatives that I used for
the bulk of the tricolors I made in the years up to 1999. So while
some people will need to go some lengths to accommodate the
characteristics of their printers to the needs of gum, others will
not; it's not a requirement for a successful gum print but simply an
as-needed adjustment to a given printer.
Katharine
On Apr 28, 2006, at 10:48 AM, Ender100@aol.com wrote:
> Yves,
>
> The gum variables can be modified to change the Exposure Scale of
> the printing. If you first adjust the density range of the
> negative prior to applying a curve, then you will get the maximum
> from the gum print—then the curve is only used to adjust the
> relative tonalities between DMax and Paper White. The adjustment
> of the density range of the negative is pretty important for gum,
> since it has a shorter exposure scale than many other processes
> and requires a lower density range negative. Doing this is one
> (just one) reason why Chris Anderson is having so much success with
> her tri color gum thingies.
>
> An example might be making a negative with an Epson 2200 where the
> UV transmission density of a negative using all inks can be over
> log 4.0—so if you need a negative to match an exposure scale of gum
> at let's say log 1.2, then you have a mismatch of 4.0 - 1.2 or log
> 2.8 TOO much density in the negative that the curve has to adjust
> for—that is over 7 stops! This is why you often see people using
> curves where the endpoint has been moved to reduce the density so
> the highlights won't blow out... unfotrunately for every point
> that you move that endpoint, you lose that many tones in the
> negative. You can actually use this to calculate exactly how many
> tones will be lost.
>
> Best Wishes,
> Mark Nelson
> Precision Digital Negatives--The Book
> PDNPrint Forum at Yahoo Groups
> www.MarkINelsonPhoto.com
>
> In a message dated 4/28/06 10:43:12 AM, gauvreau-yves@sympatico.ca
> writes:
>
>
>> Katharine,
>>
>> my first reply on this topic was probably the cause of the
>> misunderstanding,
>> when I read it back now I see what you mean. With the last one I
>> thought I
>> made all this as clear as I can but I'll try again. If whatever
>> you do back
>> exposing your print fails to give you a satisfying tonal
>> "delicacy" as you
>> put it, may be applying a different curve would help.
>>
>> If I understand normaly exposed gum printing (front exposed) you
>> can control
>> the distribution of pigment (tonal "delicacy") by the various
>> usual means
>> including % gum, % pigment, % dichromate, thickness of emultion,
>> exposure(s), development and physical manipulations, etc. With back
>> exposure, it seems only one exposure can be done and all I'm
>> saying is that
>> beside all the usual controls you have the possibility to change the
>> negative density (distribution) by applying some curve. Can you
>> control
>> every thing with some curve, the answer is simple no. The reason
>> for this is
>> that a couple variables of the gum process are totally independent of
>> exposure (negative densities), the pigment load, as you call it,
>> is one of
>> these, development and physical manipulations are other mean by
>> which you
>> can alter the tonal distribution, in the limit you can scrape it
>> all off
>> (the emultion).
>>
>>
>> I would certainly claim that if you maintain every variables fix
>> ie. you
>> don't change anything from print to print except the curve applied
>> to the
>> negative, you can basically obtain any tone you want between the
>> Dmax and
>> the Dmin of the print. Obviously, this fix variable gum print must
>> show
>> something usable to begin with.
>>
>> Regards
>> Yves
>
>
>
>
>
>
>
>
>
Received on Fri Apr 28 14:25:52 2006
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