 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| PhotoKB HomeDiscussion Groups Digital Photography Digital PhotoDSLR CamerasZLR CamerasPoint & Shoot CamerasFilm Photography 35 mmLarge FormatMedium formatDarkroomFilm and LabsOther EquipmentPhoto Technique Nature PhotographyPeople PhotographyTechnique GeneralGeneral Photo Topics General TopicsAustralian PhotographyUK PhotographyDirectoryPhoto Clubs |
Photo Forum / Film Photography / Darkroom / August 2004phenidone, benzotriazole and bromide
All, I have a question about potassium bromide in phenidone based developers. The formula for ID-68 is : Ilford ID-68 Buffered Borax Phenidone Fine Grain Developer Water, at 125°F 750.0 ml Sodium Sulfite, dessicated 85.0 grams Hydroquinone 5.0 grams Borax, granulated 7.0 grams Boric Acid, crystaline 2.0 grams Potassium Bromide 1.0 gram Phenidone 0.13 grams Water to make 1.0 liter Here, the mixture of borax and boric acid wll maintain a fairly low pH, low enough such that hydroquinone can't actualy develop film, but just regenarates phenidone. Then, this formula should contain benzotriazole to restrain phenidone. Instead we see Potassium bromide, which is supposed to be rather ineffective with phenidone, but highly effective with Hydroquinone! Can anyone throw some light on this? OTOH, ID-62, a paper developer, has both bromide and benzotriazole, which is understandable since with carbonate acting as the alkali, both phenidone and HQ need to be restrained. Thanks, Sreenath > All, > [quoted text clipped - 29 lines] > Thanks, > Sreenath I am not quite sure why but have asked an expert photo chemist about it and will post back if I get an answer. I can say that Phenidone is not insensitive to Bromide, just less sensitive than other developing agents. Hydroquinone, OTOH, is one of the most sensitive. The effectiveness of anti-foggants also depends on the pH of the solution. More later, I hope, stay tuned...  Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > All, > [quoted text clipped - 29 lines] > Thanks, > Sreenath At this low ph, the bromide is effective. As Richard has already posted, phenidone is sensitive to bromide (although less than to benzotriazole). Crawley, of FX devs fame, feels that bromide as a restrainer gives better acutance than benzo (see Anchel & Troop). Could this be the reason? Jorge > All, > [quoted text clipped - 29 lines] > Thanks, > Sreenath > As Richard has already posted, phenidone is sensitive to bromide > (although less than to benzotriazole). > Crawley, of FX devs fame, feels that bromide as a restrainer gives better > acutance than benzo (see Anchel & Troop). > Could this be the reason? Some of his formulae use both. > Jorge > [quoted text clipped - 31 lines] > > Thanks, > > Sreenath > All, > [quoted text clipped - 29 lines] > Thanks, > Sreenath Regeneration is only one of several theories of synergism. Hydroquinone does develop at low pH, but has a long induction period. I prefer not to try to separate the functions of primary and secondary developers so neatly. As soon as development in hydroquinone begins, if there is sulfite in the solution, hydroquinone monosulfonate is formed. This is a more active developer than plain hydroquinone and is perhaps the reason hydroquinone has a reputation for high contrast. It starts slowly and accelerates. Anyway, bromide does have an effect on PQ developers. It is supposed to be at least partly responsible for edge effects, in that soluble bromide is formed from silver bromide during development and restrains development near areas of high density. if you believe that HQ monosulfonate is a stroner developing agent than hydroquinone, then consult scientific literature, compare half-wave potentials, rate of diffusion, kinetics etc. ------------------------X > As soon as development in hydroquinone begins, if there is sulfite >in the solution, hydroquinone monosulfonate is formed. This is a more >active developer than plain hydroquinone and is perhaps the reason >hydroquinone has a reputation for high contrast. "friend®" wrote: > if you believe that HQ monosulfonate is a stroner developing agent > than hydroquinone, then consult scientific literature, compare [quoted text clipped - 5 lines] > >active developer than plain hydroquinone and is perhaps the reason > >hydroquinone has a reputation for high contrast. I got that bit from "Theory of the Photographic Process" which is quite well known and is a compilation of articles by recognized authorities in the field. > "friend®" wrote: > [quoted text clipped - 11 lines] > well known and is a compilation of articles by recognized authorities in > the field. Also, The MSDS for Kodak E6 first developer lists potassium hydroquinone monosulfonate as the only developing agent. This probably means that it also contains a phenidone derivative that is not in amounts sufficient to be considered worth mentioning, but if hydroquinone were as active or more active, it would surely have been used, since first developers are generally high contrast developers. >> "friend®" wrote: >> [quoted text clipped - 18 lines] >active, it would surely have been used, since first developers are generally >high contrast developers. Logical, but not true. I once knew the published explanations for "infectious" development of Hydroquinone but have just not had an interest in the subject and can;t recall right now. What I do recall was that the creation of the monosulfonate was not it. The use of Potassium Hydroquinone Monosulfonate as the other ingredient in E6 First Developer was explained in a Kodak paper, excerpted in Dignan's Photo. Kodak used it in amounts approximating double that of Hydroquinone in order to obtain the same level of activity, as the Monosulfonate was "half used up". The benefit stated was that this "half used" state allowed the developers activity to be fine tuned and to be made more stable. Maybe. In any event, the Hydroquinone Monosulfonate was not regarded as more, but rather, less active than good old Hydroquinone. Robert Vervoordt, MFA > >> "friend®" wrote: > >> [quoted text clipped - 38 lines] > > Robert Vervoordt, MFA Even so, it has some activity that is not present when hydroquinone is used without sulfite. The monosulfonate cannot be formed in that case, and the activity is lower because, it appears, the synergism between phenidone or metol and hydroquinone is not activated. Furthermore, hydroquinone without sulfite is a staining developer related to catechol and pyrogallol. One theory has it that the monosulfonate is a product of the reduction of silver halide by the hydroquinone in the presence of sulfite. Whatever the theory, the fact is that phenidone is not used up until the hydroquinone is gone. Fully oxidized phenidone cannot be regenerated by hydroquinone. The amount of phenidone required to make a very active developer with either hydroquinone or ascorbic acid is so small that, by itself, it would take forever and a day to develop an image, but actually never would because it can't reduce that much silver. The activity of a developer containing 0.1 grams/liter of phenidone increases with addition of hydroquinone until at least 8 grams of hydroquinone have been added. Adding more causes very little increase of activity, but provides an increase in capacity. At any rate, the major developing agent in most PQ developers is the Q, and they are affected by bromide content. A pure phenidone developer is a different animal. Early research I saw reported showed that up to about 1 g/l of KBr the activity of a phenidone developer increased. |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.