Does it need to be totally halftone, or just "very high contrast"? Not that these other formulas are not superior, but plain Dektol does quite a job of giving high contrast results on that film.
"Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."
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For my project I need totally halftone.
Originally Posted by 2F/2F
Originally Posted by sanking
To get true Kodalith contrast, you actually need both a Kodalith film and a Kodalith developer. The film itself was specially made to have higher than normal contrast for a film material, and to be especially sensitive to the Kodalith developer.
This is incorrect. I guess you can't trust everything you read on the internet. That said...
Originally Posted by Ian Grant
Paraformaldehyde is the condensatoin product of formaldehyde, that is, formaldehyde can polymerize with itself and form a solid material. If you let a bottle of formaldehyde solution sit around long enough, you may find that it's got a layer of white goo on the bottom of the bottle. That's from the formaldehyde in the formalin condensing and making paraformaldehyde.
And as PE showed, paraformaldehyde has no sodium in it, so there's no way it can dissolve in water and form sodium hydroxide and formaldehyde. PE mentions that it forms 6-membered rings, but it can also forms a monomer containing up to around 100 formaldehyde units.
It's soluble in dilute acid and base solutions, as they both hydrolyze the paraformaldhyde back into formaldehyde.
Sandy, you asked what the paraformaldehyde did in the D-85 formula - I suspect it's there to harden the emulsion. Perhaps PE can address this.
Anyway, I've used the D-9 formula given below with Kodak LDP-4 direct reversal copy line film with good results.
For up from the ashes, up from the ashes, grow the roses of success!
Kirk: When paraformaldehyde dissolves in water it creates a basic solution, I think that's what Ian was refering to. As I'm sure you know, most of our developing agents are base catalyized, thus if there was no other agent to turn the developer basic, it was near inactive.
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Kirk, I don't disagree about Paraformldehyde, (polyoxymethylene), but the reference I saw was to how it formed formaldehyde & sodium hydroxide in D85, there's plenty of Sodium ions in the solution, and in the Agfa Ansco equivalent AN79 Potassium ions as well.
After I found D85 made up with 7.5ml Formaldehyde solution in place of Paraformaldehyde barely even tarted to develop lith & line films I measured the pH of. It wasn't alkaline, it's 30 years ago so I can't remember the exact pH meter reading now
Kodak now use Sodium Formaldehyde Bisulphite instead of Para-formaldehyde in Kodalith developers and a part B of Sodium/Potassium Carbonate and usually Sodium/Potassium Hydroxide.
Paraformaldehyde in water is neutral so where else is the alkali needed for this lith developer to work coming from ? The developer needs a working pH of around 10. There's a reaction somewhere between the Paraformaldehyde and most likely the Sulphite or (Meta)bisulphite that's generating the hydroxide ions.
Sandy, this Reprolith developer (D85/AN79) gives excellent edge effects on all the lith/line films I've used, and was far superior to any of the non formaldehyde types of developer, which is it's why it's still in production today although the formula has evolved.
Last edited by Ian Grant; 02-22-2009 at 06:30 AM. Click to view previous post history.
Reason: too many typos
Sandy, search Google for, lith formulas . I've used
a variation on Wall's Normal Hydroquinone with some
success with paper. As with most lith formulas it was
designed for film. Very simple. No guarantee. Dan
Perhaps I can almost trust what I read after all
Originally Posted by Kirk Keyes
You'd be right to say the statement was simplistic though as it doesn't say what happens with the formaldehyde.
A quick Google search shows the Formaldehyde-Sulphite Clock reaction, and this can take an essentially acidic sulphite/(meta)bisuphite & formaldehyde solution from a pH of less than 7 & turning it to pH between 9-11. The reaction uses H+ leaving an excess of the hydroxide ion -OH,
This is quite obviously the explanation for how D85/AN79 works, it's quite possible if I'd added substantially more than 7.5ml of 40% Formaldehyde and waited sometime for the clock reaction to occur I wouldn't have needed to add a Part B
So yes, the Paraformaldehyde dissolves, forms Formaldehyde, which in turn reacts with the Sulphite/(meta)bisulphite and liberates the hydroxide ion, which in turn forms Sodium or Potassium Hydroxide.
Actually, any aldehyde reacts with sodium sulfite to form an aldehyde.sulfite adduct. (actually, I believe it is the bisulfite adduct to be more precise). This product is a solid white powder that dissolves in water and can be used for timed release of aldehyde. (see my patent or Kodak pre-bleach formulas for examples)
Formaldehyde also reacts with itself to form a variety of cyclic and polymeric structures of the type stated above, and these can be dissolved in either acid or base to release the original formalin.
Aldehydes also are powerful reducing agents, formalin being at the top of the list. (reducing agents can be developers).....
Therefore, use of formalin or paraformaldehyde in alkali will give you a stronger developer with lith like properties due to the formalin and the increase in pH. The reaction (CH2O)n -> CH2O is electronically neutral to appearances, but is going from a "neutral" species to a reducing species.
http://www.chemindustry.com/chemicals/725857.html or here http://en.wikipedia.org/wiki/Paraformaldehyde
Formaldehyde is a developing agent or reducing agent with low discriminating powers. It fogs film when used as a hardener and has been abandoned in the industry for this purpose. It is very toxic and is suspected as being a carcinogen.
The original formula may be incomplete in that it may not contain enough alkali to do the entire conversion job. I have seen some formulas with NaOH in them. I have also seen (IIRC) formulas with acetone in them. Someone should chime in here on that one as acetone is much less toxic!
The whole formaldehyde-sulphite clock reaction starts without any alkali, so that's why D85 seems incomplete at a first glance, It seems that it's the balance of Formaldehyde, sulphite and (meta)bisulphite that's critical to when the pH suddenly switches from mildly acidic to highly alkali. It doesn't happen immediately either. Kodak & Agfa Ansco were obviously using this specific reaction.
Originally Posted by Photo Engineer
Kirk may well be able to tell us more.