Digital BW, The Print

Hello Mark,

  thanks for your precious information. I will save them in my notes.

I fully agree with you. The testing machinery you and few others have put up is of paramount importance for all of us. Nonetheless, we should also not forget centuries of experience with  traditional materials. I have chosen gelatine because it has been successfully used since very long time in sizing or coating papers. Ditto for carbon pigments (think at china inks, for example). Silver gelatin paper has been long enough to guarantee good archivability when, as you have pointed out, prints are properly stored. Unfortunately, most of the secrets of gelatine coating belong to photographic paper manufacturers.

Many have correctly observed that gelatine coating is not for the occasional printer not for the hobbyistG604T_WIRELESS. They are, indeed, right. Coating larger paper sizes is very cumbersome and it requires proper equipment. I apologize to those who are getting bothered by the related threads or are not interested in them.

Ciao,

   Mantinieri

http://www.mantinieri.com

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Mark" <mark@...> wrote:
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> Gelatin is an amazing polymer with fascinating properties that enable traditional photographic processing.  It's a hard dry polymer with protective barrier properties when it's below its glass transition temperature (Tg), but it moves to a highly permeable gel state when above Tg. The Tg of most polymers is fairly independent of humidity, but not so with gelatin. This relatively unique property of moisture content influence on the Tg is a "two-edged sword". It makes conventional film and photo paper processing possible, but it creates a long term environmental weakness for the image.
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> We take it for granted that gelatin goes into a gel state and becomes highly permeable when it gets immersed in water.  Gelatin is above Tg when wet. However, gelatin actually reaches Tg and switches to the gel state when the humidity at typical room temperature (approx. 21C/70F) reaches about 75%RH (a common real-word event in many areas of the world). Ever seen a traditional silver-gelatin print with silver tarnish or stuck to glass in a frame? That's a common outcome of a traditional photographic print traversing the glass transition at typical room temperatures due to prolonged high humidity events.  We need gelatin's Tg properties to carry out the chemical photographic process, but I'd probably choose something else if I'm looking for long term protection of inkjet colorants underneath a post coating treatment. 
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> Gelatin also has some fascinating anisotropic physical properties that chemical hardeners (e.g. formaldehyde) can significantly influence, but I'll save that discussion for another day. 
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> Acrylic polymers like Premier Print Shield have a pretty good track record and are widely used to protect paintings these days (especially paintings done with acrylic paints).  Research at both Wilhelm Imaging Research and Aardenburg does suggest for the most part that acrylic coatings cut down on photo-oxidation of pigments so improve lightfastness, gas fastness, etc.  However, the costs, the need for good ventilation during application, and application challenges of spray or roller coating without defects means there is no free lunch in the quest for durable, abrasion resistant coatings.
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> cheers,
> Mark
> http://www.aardenburg-imaging.com
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