Re: lith film

[Richard Knoppow <dickburk@ix.netcom.com>]

----- Original Message ----- 
From: "Dave S" <fotodave@dsoemarko.us>
To: <alt-photo-process-l@usask.ca>
Sent: Saturday, September 13, 2008 5:29 PM
Subject: RE: lith film


> > I also don't at this moment recall the names of official
> > restrainers, but if you look in the formula books under 
> > "soft
> > working developer", they probably name some.  Or, if he's
> > around, Dave Soemarko will know....
> Goodness, I used to get so much into those stuffs, and I 
> can't believe it that
> my memory is fading too. Is it something bromide? maybe 
> potassium bromide? And
> then there is another popular restrainer too, but I forgot 
> what that one is. If
> Richard Knoppow is around, he will know.  :-)
>
>
> Dave
    The most common anti-fog agents are potassium or sodium 
bromide and benzotriazole. The effectiveness of both varies 
with the pH of the developer. Benzotriazole is supposed to 
have less effect on film speed for a given amount of fog 
suppression.
    Very low contrast developers depend more on the type of 
developing agent and pH than on restrainers. The lowest 
contrast developer is probably Phenidone in a sodium sulfite 
solution. The well known POTA developer is of this type. 
Phenidone, and its derivatives such as Kodak Dimezone, are 
inherently very low contrast and in "normal" developers are 
usually used with a second developing agent.
    The contrast of lith film is mostly a property of the 
emulsion. Silver halide particals vary in their sensitivity 
to light, a normal pictorial emulsion, intended to record a 
wide range of brightness linearly, has a wide range of 
particals of varying sensitivity. A high contrast film has a 
much narrower range. While special developers can produce 
continuous tone negatives from high contast film its always 
a bit tricky because the film is designed to do just the 
opposite, that is, to have a sharp demarcation of 
sensitivity so that just above it will produce maximum 
density and just below it no density at all. Special 
developers are used to enhance this effect.
    --
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com