Digital BW, The Print

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—both 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—the 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—smells 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 — 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.

Paul
www.PaulRoark.com 





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