I agree with you.
Originally Posted by Photo Engineer
Of course, they are different; one is a gas, the other is it's solution.
Formaldehyde contains no water.
Ted actually points out terms that have been deprecated.
(but makes an error at one point describing a 10% solution)
Anyway, we often say formaldehyde when we should say
"a formaldehyde solution" (or "formalin").
I might be mistaken, Tim Rudmen's book on Lith printing is at home, but I believe that other function of the formalin is to "bond" the sulphite ions (I believe PE referred to it, if I understood him correctly). To be able to do Lith printing (on certain B&W papers that is) infectious development should take place. For this process as little or no Sulphite should be freely present..
Originally Posted by sanking
My post 27 mentions the connection twixt formaldehyde
Originally Posted by Cor
and sulfite. There is a bonding. Sulfite levels must be kept
low so that infectious development may take place. At the
same time developer longevity requires a preservative.
So, the formaldehyde. Apparently sulfite combined
will not retard infectious development while that
free in solution will retard development.
Likely sulfite levels should not exceed bonding capacity.
Formulators may wish to keep that in mind. Of course
no formaldehyde is necessary where short tank or
tray life is expected. In the little lith work I've
done none was used.
That I believe is the only reason for the formaldehyde;
maintaining the presence of a preservative, sulfite, in
some quantity above a lith developer's in solution
Wall's Normal Hydroquinone is a most basic lith
Originally Posted by Ray Rogers
developer; hydroquinone, sulfite, carbonate. Like
the other two, 81 and 85, it is a film developer.
Any of the three will do for paper when very
dilute. IIRC only 85 uses formaldehyde. Dan
Formaldehyde is in Reprolith - Agfa Ansco 79 & 79b, Kodak D85 & D85B, Dupont LD1, Dupont 7D, Ilford Formalith and other more obscure lith developrers, as well as a whole host of commercial lith developers from a variety of companies.
It's fair to say that virtually every manufacturer supplying the graphics trade produced a formaldehyde based Lith developer because these developers have very significant advantages over other high contrast developers for many types of graphics work.
Kodak now use Sodium Formaldehyde Bisulphite in most of the various types of Kodalith, these are all derived from D85.
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Kodalith halftone developing: any update?
I just came across this discussion on your Kodalith halftone development options....
have you, or others any updates for us? Muchly appreciated....