[alt-photo] Re: 3 color gum and PDN calibration?

[Christina Anderson]

Dear Brian,
I've had S. Gayle Stevens here this week doing wet plate collodion with my students and what a blast. I think all 100 majors are jumping ship to wet plate or to her program in IL to just be around her and absorb her energy. Hence my late reply to this email. My experimental class was doing wet plate in the Holga camera, SO cool.

 I agree with Henry that yellow is longer than the other two exactly as he says. In practice, how this translates (loose, like everyone else recommends) is my timer is usually at 6 minutes and then pull the cyan and magenta at about 5 and the yellow if I forget to walk in there for several minutes I don't care. If I forget on blue that is a different story. Busted.

This can also depend on what layer order the color is in, too, with exposures erring to longer the more layers. Another reason why a standard printing time for any color has to also take this into account at times and is also what makes gum so loose.

Red is also longer for me, way different from the bluer magenta. I pay attention a bit more closely to the red exposure depending on whether an orange red or not.

This sounds weird but with gum, it is not like platinum where you have a very particular window of correct time, the solution sinks into the paper and either you nailed it or you didn't. With gum, you are hardening an increasingly thicker layer of goo on top of the print; a one-minute exposure will have a thinner paler layer, longer thicker and more saturated. This translates to an ideal RANGE of exposure that is very forgiving. It is not the same as standardizing a time a la PDN in other processes. More latitude in both exposure and development. However, of course contrast goes down with more and more exposure as do other factors change but you already know this.

The yellow of the dichromate will turn to brown and get increasingly darker to a dark brown and even with an intense clearing of a step wedge can slightly influence the color yellow to give a false read of no two steps merging. It is a difficult color to judge. Yellow is also impossible to judge at night but should be evaluated in daylight if possible.

I wanted to share what I have read about color order. I personally have no problem with cyan first, even as a thalo, but do agree it is a tough cookie in the stain dept. I dilute it quite a bit, though: 1 tube in 250-500ml gum. I then print yellow and then magenta and a final coat of thalo again if it is needed. BUT I have read in a few books the practice of printing first a blue, then magenta to get the contrast of the print and then multiple layers of yellow to color balance. I find this an intriguing idea because I have just never printed yellow last. I think this practice comes from the printmaking industry but with transparent yellows that I use it is definitely worth a try, this idea of contrast adjustment first and color balance last. Does anyone on the list print this order and find it preferable?

Chris

Christina Z. Anderson
christinaZanderson.com

On Sep 27, 2012, at 2:11 AM, Henry Rattle wrote:

> Just in case it's relevant here, I found it impossible to judge the yellow
> under fluorescent light of any kind. There are quite a lot of missing
> wavelengths in the yellow region of fluorescent tubes/energy-saving bulbs,
> so you don't get a true impression.
> 
> For the record, I use W&N Permanent Rose (PV19), Winsor Blue (Green
> tint)(PB15), and Winsor Yellow (PY154) and find that yellow requires about
> one-and-a-half times the exposure (12 min against 7 min) of the other two.
> 
> Best wishes to you all,
> 
> Henry
> 
> 
> On 27/09/2012 07:17, "Loris Medici" <mail at loris.medici.name> wrote:
> 
>> Johnny, I kinda agree with the comment below.
>> 
>> Just for the records / for the case you may feel the need for an
>> alternative method in the future:
>> 
>> - Calibrate for a much more simpler / stable (in terms of consistency,
>> number of parameters and ease of calibration) process such as
>> cyanotype, p/pd and such (shorter scale processes are better, since
>> gum also has a relatively short scale)
>> - Find the correct pigment-dichromate ratio, exposure time and
>> development regime to suit the negative for each separations. I mean:
>> Don't confine yourself into a strict set of parameters, use the
>> flexibility of gum! It would be a good exercise in exploring /
>> learning the capabilities of the gum process too!
>> 
>> Hope this helps somehow,
>> Regards,
>> Loris.
>> 
>> 2012/9/27 Mary <gneissgirl at spamcop.net>:
>>> ...
>>> I have to admit that after struggling with PDN for calibrating gum, I kind
>>> of gave up. I just didn't have the patience to deal with it. I remember
>>> yellow being particularly frustrating. I admire your tenacity!
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