Digital BW, The Print

ender100 wrote:
> Hi Paul,
> 
> You asked for comments, so here goes!
> 
> Actually gum was used in gum bichromate prints and carbon prints are done with a gelatin base\u2014both gum and gelatin are colloids that are made sensitive to UV light and harden when Ammonium or Potassium Dichromate is added to them and they are allowed to dry.  They can be used with any color of pigment\u2014the more stable the pigment the more stable the print.  You can also do color separations and make full color gum and carbon prints by doing 3 printings.  Carbon tissue is also used in the photogravure process.  Eggs can also be used as a colloid with the dichromates.  Gum prints and carbon prints are two of the most stable prints known.
> 
> All these processes use negatives for contact printing with UV light, so the negative has to be the size of the final print..  Currently a lot of people are making digital negatives rather than shooting large in-camera negatives or using wet process enlarged negatives.
> 
> If you experiment with gum, you need something to keep it from spoiling\u2014smells nasty then!
> 
> I do primarily Platinum/Palladium printing with digital negatives and am experimenting with polymer plate photogravure, which is turning out very nicely.
> 
> Sorry \u2014 don't mean to be picky, 
> 
> Best Wishes,
> 
> Mark Nelson
> Precision Digital Negatives
> PDN Print Forum @ Yahoo! Groups
> Mark Nelson Photography
> 
> 
> On Nov 28, 2008, at 10:50:51 PM, pr_roark <pr_roark@...> wrote:
> From:   pr_roark <pr_roark@...>
> Subject:    [Digital BW] Pigment Stabilization
> Date:   November 28, 2008 10:50:51 PM CST
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> In my latest efforts, I've been reading up on and starting to 
> experiment with ways to increase the stability of the carbon pigments. 
> 
> One of the more interesting and intriquing factoids I've found is that 
> Gum Arabic has been used to disperse and stabilize carbon inks for 
> quite a while -- like maybe three thousand years. Yet in efforts to 
> disperse and stabilize the latest carbon nanotubes, Gum Arabic is still 
> one of the best. Additionally, it's safe and in lots of our foods. It 
> is also one of the ingredients in the old carbon photographic printing 
> process and is available from Photographers Formulary.
> 
> I'll be experimenting with it and attempting to use a centrifuge to do 
> accelerated settling testing of different pigment dilution bases and 
> approaches. 
> 
> I'll post some of my latest notes and thoughts at 
> http://www.paulroark.com/BW-Info/Pigment-Stabilization.pdf
> 
> Chemists and others, please don't hesitate to correct things I've 
> posted if they are wrong (and clearly incomplete). I make no claims to 
> expertise here. I'm just a curious B&W photographer exploring my new 
> medium.

Good dispersion qualities but if it is tends to spoil it 
will spoil in printers and that's one of the worst things 
that can happen in a printer. Had some bad luck with an 
Epson 5000 a CIS and  dye inks that got wrong. No fungicide 
etc that could keep the tube system clean.

The hardening of gum arabic in the alternative processes 
could be simulated in inkjet printing with a clear diazo 
component mixed in that hardens the PVA or gelatine medium 
with UV light after printing. Bichromates are not 
recommended. (Form)aldehyde vapor could do the same after 
printing and doesn't have to be mixed in the ink.
It's patented for hologram hardening but not for inkjet yet 
I guess. Maybe tomorrow. Not a healthy process  either. 
There will be inkjet papers with a coating that cross link 
the ink medium they are intended for, we are probably using 
them and see their better waterproof resistance already.

Lately we see more messages here that praise the pre inkjet 
technologies for their archival qualities. Thousand of 
chemists work on inkjet inks and coatings, there must be 
some that are well aware of the pros and cons of the old 
processes and use them were suitable. At the same time they 
must also be well aware of all the new chemistry that is 
available for inkjet ingredients.

-- 
Met vriendelijke groeten, Ernst


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