Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,573   Posts: 1,545,671   Online: 892
      
Page 2 of 4 FirstFirst 1234 LastLast
Results 11 to 20 of 36
  1. #11

    Join Date
    Jan 2005
    Location
    Boston, MA
    Shooter
    Multi Format
    Posts
    1,416
    Manganese (II) sulfate is mentioned in some old literature like Duffin, but I do not see it used as a stabilizer in vast number of modern emulsion patents. I have tested it but it has little power to halt the sulfur sensitization reaction. Jim Browning may have a different intention, but I am not certain if that's a useful agent as a stabilizer on optimally sulfur sensitized emulsions. Manganese ion may adsorb on crystal surface to restrain the ripening effect, though, and it may be effective for this type of problems, but organic antifoggants (like PMT and 2-MBI) are so much more effective.

    These days, manganese compounds are rather used as an electron trap as a dopant. However, for this application, some other metals are more common (iron, ruthenium, iridium, etc.). Rhodium and palladium are also effective dopants for chloride emulsions.

    Sodium azide is used as a biocide, not as an emulsion stabilizer. This agent is toxic and also can get involved in a number of other reactions, so I prefer some other agents, such as sodium salt of 2-phenylphenol, methylparaben, any of the isothiazolinone agents. Look up biocide on my website and you'll find a whole story.

  2. #12

    Join Date
    Jan 2005
    Location
    Boston, MA
    Shooter
    Multi Format
    Posts
    1,416
    Addendum.

    In photographic chemistry, terms "stabilizer," "antifoggant" and "biocide" are given some specific meaning, although some authors use the terms less distinctly.

    Emulsion stabilizer is an agent used to minimize the fluctuation in emulsion speed and fog level over the course of storage time by inhibiting any further chemical sensitization. TAI is a very good example of this. This agent was introduced by Birr in 1920s in Germany and it is still VERY commonly used today. This agent somehow binds to sulfur sensitizing agent in the gelatin-water phase and prevents them from entering sulfur sensitization reaction.

    Emulsion antifoggant is an agent that forms very insoluble silver compound and covers the surface of silver halide crystals. Some compounds make less soluble silver salt than others. These antifoggants also vary in the strength of adsorption on the silver halide crystals. PMT and MBI are very good examples of antifoggants that form very insoluble salt (comparable to AgI) and they also adsorb very strongly on silver halide as well as metallic silver. 1H-benzotriazole (familiar in developer use) makes silver salt that is more soluble than silver-PMT or MBI, and adsorption is also considerably weaker. Plain benzotriazole can be desorbed by color developers (which has stronger adsorption on AgX crystals) and this agent is not very effective at all in color materials. 5-methylbenzotriazole is improved in this regard . Plain benzotriazole is usable for b&w emulsions, but not as effectively.

    Some of the effective antifoggants make very dense assembly of antifoggant molecules on the crystal surface, and they can practically halt ostwald ripening process. Some are not as drastic but greatly slow the ripening process. Therefore, these compounds are also called "restrainer" in precipitation, growth and ripening contexts.

    Biocides are self-explanatory.

    Extra material.

    What if you have a restrainer that preferentially adsorbs on one surface over the others? These compounds are used to control the shapes of crystals in highly sophisticated emulsions. Silver chloride usually does not make tabular crystals, but some of these "crystal habit modifiers" can be used to make silver chloride tabular grains. Joe Maskasky is the pioneer in this field. Some of these compounds, as well as some dyes, are used to make exceptionally thin tabular crystals of very large diameters (very high aspect ratio). These crystals have some useful properties, but they are also easy to break by mechanical stress (and can fog or lose sensitivity) and they are hard to use for practical applications.

  3. #13
    AgX
    AgX is offline

    Join Date
    Apr 2007
    Location
    Germany
    Shooter
    Multi Format
    Posts
    8,616

    Birr

    To my information it was in the late twenties that by two other Agfa people (Mathies/Wendt) the predecessor of that stabilizer was found, a sulphur containing heterocycle. Birr came to Agfa only in ’34 and found TAI in 1937 (after the presentation of the New Agfacolor film).
    But I admit finding these dates is difficult and the results are not necessarily trustworthy as long one did not see the original documents, which I did not.

  4. #14

    Join Date
    Jan 2005
    Location
    Boston, MA
    Shooter
    Multi Format
    Posts
    1,416
    That's right, it was in 30s. I have the literature detailing these but didn't consult it when I wrote the above. Birr has a couple of famous quotes and I remember one from 20s, so I often get confused...

    Helmut Mueller worked with Koslowski and Birr at Agfa before the war, and moved to Ansco/GAF after the war. So I trust his accounts of pre-war AGFA Wolfen research. Fritz Wentzel is another German chemist I respect but I think he moved to the US in 30s. Ira Current worked under him and I heard a lot of stories about how they worked together.

    I have his photographic chemistry book from 20s (in German) but haven't had it translated. His memoir (in English) has lots of bits of very interesting information.

  5. #15

    Join Date
    Jan 2005
    Location
    Boston, MA
    Shooter
    Multi Format
    Posts
    1,416
    Note for chemical shoppers: 6-nitrobenzimidazole and 5-nitrobenzimidazole are the same compound. 5 and 6 positions refer to the same thing in benzimidazole.

  6. #16

    Join Date
    Oct 2006
    Shooter
    Medium Format
    Posts
    131
    Quote Originally Posted by Ryuji View Post
    This book is actually pretty good, but it is also highly advanced for most amateur emulsion makers.
    Glafkidès, Chimie et physique photographique (there's an English translation available) and Frieser et al., Grundlagen der photographischen Prozesse mit Silberhalogeniden (I think the authors are somehow related to Agfa-Leverkusen – I am not aware of an English translation though) have nice chapters on emulsion stabilization.

  7. #17
    AgX
    AgX is offline

    Join Date
    Apr 2007
    Location
    Germany
    Shooter
    Multi Format
    Posts
    8,616
    Hologram,

    Frieser was holding chair for scientific photography from 1936-45 and was head of research at Agfa-Leverkusen 1952-?

  8. #18

    Join Date
    Jun 2007
    Shooter
    ULarge Format
    Posts
    67

    Sodium Azide

    Quote Originally Posted by rmazzullo View Post
    reference regarding Sodium Azide (which is an explosive):

    http://www.apug.org/forums/forum205/...trix-film.html

    Bob M.
    Sodium Azide was an additive used by Fotokemika as a preservative - that is to prevent disintegration of the uncoated emulsion prior to coating and drying. I never used it, but I updated the formulation to reflect the FK additions of Sodium Azide, and the PMT. I should probably replace this with Thymol as it is safer to use.

    As far as the Manganous Sulfate, since it was mentioned in the Duffin book, I used it from the beginning. I don't know if it has any effect on the emulsion, and can probably be omitted.

    Regards - Jim Browning

  9. #19
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,037
    Images
    65
    Antifoggants such as PMT must be used with care. Taking Jim's emulsion as an example, if one were to spectrally sensitize it, there might be an interaction between adsorbed species such as PMT and the dye. I have seen PMT unsensitize an emulsion by 'kicking' the sensitizing dye off the grain either immediately or gradually with resulting speed losses.

    If mixed emulsions are used such as in a mixed R/G/B set for pan sensitivity, or if coating a VC emulsion set, interactions between emulsions are common. It is therefore necessary to use ballasted versions of many of these compounds to isolate them to the preferred emulsion. An alternative is to use a very strongly adsorbed chemical which is tailored to have the desired activity, but then this has implications on use of the sensitizing dye.

    When coating on RC or film, the formulas can be virtually the same, but on FB papers, the equillibration of all chemistry into the paper can lead to changes in speed and fog. Therefore, as is often the case, FB materials use a different formula, or keep more poorly than their RC counterparts.

    PE

  10. #20

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    "Ballasted"? Adding a larger ligand (in the biochem sense, I think) or other compound to make the functional part of the compound heavier/less mobile so it doesn't leave the intended layer?

Page 2 of 4 FirstFirst 1234 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin