Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,223   Posts: 1,532,514   Online: 1125
      
Page 9 of 9 FirstFirst ... 3456789
Results 81 to 85 of 85
  1. #81

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,609
    An interesting sidelight, depending on alkalinity, Phenidone derivatives with hydroxymethyl substitutions in the 4 position, such as Dimezone, have been show to be very effective at tanning (without staining), as opposed to Phenidone which does not tan. And apparently since the tanning action of these compounds has to do with aldehydes rather than quinones (as is the case with Pyro, HQ, Catechol etc.), considerable amounts of sulfite can be present without inhibiting gelatin cross linking since sulfite doesn't remove the aldehydes.

    This, I think, is a potentially important difference between Phenidone and Dimezone which is rarely if ever mentioned, particularly in discussions regarding the substitution of Dimezone in place of Phenidone. Usually the assumption is that with an appropriate adjustment based on molecular weights, Phenidone and its common derivatives are functionally the same except for differences in stability and solubility.

    I had completely forgotten about this until a few days ago. I wonder how much sulfite and/or ascorbate can be present, and what effect the pH has on the tanning action of Dimezone. In U.S. Patent 3,453,109 a substantial concentration of carbonate alkali was used.

  2. #82
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,972
    Images
    65
    The patent is by Bill Lee. Sylvia and Dick Dickenson worked for him, and when Dick Henn retired, Bill took his place. When Bill died unexpectedly, Dick took his place. Then it was the fateful year of 1988.

    Just a bit of history to add to this.

  3. #83

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,609
    Interesting. Thanks. I didn't realize Lee was one of the honchos.

  4. #84

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,609
    PE - regarding tanning developers - not necessarily Dimezone - but the usual tanning/staining formulas using hydroxybenzenes in low sulfite (Pyrogallol, Catechol mostly). Normally we think of the tanning reaction between these oxidation products and gelatin as a "hardening" or "insolubilizing" of the gelatin (cross-linking etc.). But if we consider current B&W films with their pre-hardened emulsions, does tanning have any further effect?

    For example one of the purported beneficial effects of tanning developers is a hardening of the emulsion imagewise, which is said to prevent the active developer from diffusing into the deeper layers of the emulsion in areas of high exposure, which in turn means not only lower developed density, but also reduced effects ot irradiation and halation (which are both effects that increase the deeper you go into the emulsion). With an older unhardened, or matrix film, this makes sense. But does it work with current films?

  5. #85
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    22,972
    Images
    65
    Michael, as the factory hardness goes up, the user ability to harden goes down! Therefore, today's films are not very sensitive to tanning, but they do stain with some of the staining developers. But, even that can be reduced.

    PE

Page 9 of 9 FirstFirst ... 3456789


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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