There are a many gelatin types for making silver gelatin emulsions and most current textbooks don't discriminate between them. Here is some terminology to help you out.
1. Food gelatin: These are active gelatins with lots of additives. At my current estimates as little as 30% of the weight is really gelatin in some brands. Using these can lead to foggy emulsions.
2. Active gelatins: These are active gelatins that interact with an emulsion during making and can cause increases in speed and contrast. They are loaded with thoureas and allyl thioureas. For those concerned about the toxicity of thiouread, be forewarned that it is a natural product in gelatin due to the cows and pigs eating mustards. They can lead to foggy emulsons.
3. Inactive gelatins: These have had all sulfur compounds removed. They are preferred.
4. Pig Gelatins: Not commonly used in photo materials nowdays. They have their maximum swell at pH ~9.
5 Bone Gelatins: Made from cow cartialge. Common consituent of current photo products. Minium swell at about pH 4.5.
6. Gelatin Bloom: This is a measure of gelation strenth AFAIK. We never used this at EK. In my personal experience, the higher the bloom, the higher the apparent viscosity and the less pepper grain and aggregation in an emulsion. It also gets harder with higher bloom. Lower bloom gelatin hardens more rapidly though in my experience. This is very subjective and difficult to assess.
7. PA gelatin: Gelatin treated with phthalic acid. Used in coagulation washing of emulsions (PA washing). This gelatin is softer, hardens more slowly and adheres less well unless regular unmodified gelatin is added.
Using low gelatin when making an emulsion results in larger grains and higher speed. Higher gelatin results in lower speed and finer grain. This is a generalization.
Heating gelatin for too long or at too high a temperature decreases viscosity and hardneing capability.
PE
1. Food gelatin: These are active gelatins with lots of additives. At my current estimates as little as 30% of the weight is really gelatin in some brands. Using these can lead to foggy emulsions.
2. Active gelatins: These are active gelatins that interact with an emulsion during making and can cause increases in speed and contrast. They are loaded with thoureas and allyl thioureas. For those concerned about the toxicity of thiouread, be forewarned that it is a natural product in gelatin due to the cows and pigs eating mustards. They can lead to foggy emulsons.
3. Inactive gelatins: These have had all sulfur compounds removed. They are preferred.
4. Pig Gelatins: Not commonly used in photo materials nowdays. They have their maximum swell at pH ~9.
5 Bone Gelatins: Made from cow cartialge. Common consituent of current photo products. Minium swell at about pH 4.5.
6. Gelatin Bloom: This is a measure of gelation strenth AFAIK. We never used this at EK. In my personal experience, the higher the bloom, the higher the apparent viscosity and the less pepper grain and aggregation in an emulsion. It also gets harder with higher bloom. Lower bloom gelatin hardens more rapidly though in my experience. This is very subjective and difficult to assess.
7. PA gelatin: Gelatin treated with phthalic acid. Used in coagulation washing of emulsions (PA washing). This gelatin is softer, hardens more slowly and adheres less well unless regular unmodified gelatin is added.
Using low gelatin when making an emulsion results in larger grains and higher speed. Higher gelatin results in lower speed and finer grain. This is a generalization.
Heating gelatin for too long or at too high a temperature decreases viscosity and hardneing capability.
PE
