Numerous references have been made here to the fact that modern gelatins are not the same as the gelatins used in the past for film and paper manufacturing. The so-called "activated" gelatins. Since film production only slowed down about five years ago, I am curious as to why the traditional gelatins used for film/paper manufacturing went away? I know that all modern manufacturers have, I guess, figured out how to use current gelatins, but why did they have to? When did the switch occur?
Photo grade gelatin has not vanished. It is available from the Photographers Formulary and others and is made by 2 companies in the US and 1 in France.
Photo grade gelatin is oxidized deionized gelatin made extremely pure for the photo industry. Kodak uses gelatin from all 3 of these companies. It comes in several BI (Bloom Index) numbers from 75 to about 300. It also comes as a phthalated gelatin used in making emulsions. The phthalated gelatins are made in several grades too, in order to facilitate the washing step.
Old gelatins that were used for photography were impure, and contained high levels of sulfur containing compounds. That meant that old gelatins had to be graded as to their activity in photo emulsion making. All formulas published in older texts used this old gelatin which did 2 things at one time. It allowed the making and sulfur sensitization steps to be combined into one step. It also made the emulsion less predictable due to the variations in sulfur compounds.
Modern gelatins require a separate sulfur sensitization step to replace the combined steps noted above. The effect of the sulfur is very predictable and controllable.
This is a repeat post of earlier information in a thread on gelatin. There is much more information spread out here including the method of sulfur sensitization.
Actually I wanted to post the same question today...
Obviously (or not that obviously) the industry wanted to get rid of that logistical problem of having to have a lot of charges of gelatin in stock to blend the needed quality from. Which of course involved a lot sensitometric measurements too. Having a standard stock of gelatin and knowing how to impure it to what effect, makes production more lean.
But when did that happen and did the industry change over to a standard (or rather making of a standard) gelatin at the same time?
But perhaps someone out there knows the details on this decision of the industry.
Last edited by AgX; 06-25-2007 at 01:47 PM. Click to view previous post history.
The work of Mees and Sheppard at Kodak established that it was allyl thiourea in gelatin that was causing the sensitization. Their work was the first published on this subject. It led to consistant speed in film and paper thereafter.
Before that, most companies had 3 grades of old gelatin. Hard, medium and weak or soft ripening gelatin. (This is blooming in German, not to be confused with the Bloom Index which relates to viscosity. Many amateurs make this crossover in translation and try so hard to get differences in speed and contrast by varying Bloom Index when it is the wrong variable.)
The mixtures of these 3 grades of gelatin made the final emulsion have the contrast and speed that was desired, but it varied due to the diet of the cows.
This is how Mees discovered it. The cows were eating too much mustard seed and this increased the sulfur content of the gelatin and caused the Kodak emulsions to go into fog.
Kodak kept this as a secret untl the publication noted above. Therefore, they converted first to the oxidized deionized gelatins before anyone else.
I got the impression from something that someone 'in the trade' said to me recently that maybe some of the European manufacturers are still using active gelatines in their traditional emulsion films and grade them carefully to get the required degree of sensitivity, rather than relying on adding compounds to de-activated gelatine.
Can anyone confirm this?
If it is true, then active gelatines should still be available at least in Europe.
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Originally Posted by steven_e007
Active gelatin is certainly available. It is merely unrefined bovine gelatin made from bones. The problem is the variability that is associated with each batch (high, medium or low ripenining for example) and who is going to test it for the individual.
The companies surely have tests from the 1900s that still work. If you can get them to sell it, fine. I find that there are enough variables to work with that I don't want to add this as well. I find it easier to adapt a formula rather than worry about getting old gelatin.
For that matter, unflavored Knox gelatin off the shelf is probably the 'old style', but IDK. The problem is that it has only about 50% gelatin, the rest being additives. So, you only get a percentage of the gelatin you want.
In my tests, the Knox supermarket gelatin gave very poor results for my emulsions.
old style 'activated' photo gelatine
i can get non-oxidised 'activated' photogelatine purpose -made for home -brew coating
Originally Posted by Photo Engineer
$50 for 100 grs
i am not comfortable with that price yet so i haven't ordered any
is the price justifyable? my experience with gelatine home brews is to little for me to make a decision yet
what would a fair price for such a gelatine be? any ideas/input?
the maker uses it himself and i am sure that it is consistent and of a grade that is reliable-his own work is world class
just can't get myself up off of $50 to give it a try since i have so little real experience with home brew gelatine
vaya con dios