Re: ETHOL LPD

From: Richard Knoppow <dickburk@ix.netcom.com>
Subject: Re: ETHOL LPD
Date: Fri, 23 Apr 2004 07:34:54 -0700

> Phenidone tends toward bluer
> image color than Metol and does not usually produce the
> slightly greenish tone D-72 sometimes does on some paper.

I don't know if I would say that. Phenidone developers are capable of
producing warmer hues as well as greenish tint on some enlarging
papers. What you are referring to is probably benzotriazoles that are
often used in conjunction with phenidone.

> The amount of both Bromide and Benzotriazole are minimum.
> Either can be increased to modify the image tone or if one
> is working with slightly foggy paper.

I think this foggy part is an old story that should be forgotten.

First of all, one should distinguish between fogged emulsions and
developers that cause fog. The former occurs when silver halide
crystals contain silver specks that are large enough to make the grain
developable without any exposure. The latter occurs when the excess
potential of the developing (reducing) condition approaches the level
where electrons are injected to the conduction band of the silver
halide crystals (which makes metallic silver specks and then make the
whole grain developed). Benzotriazoles or free bromide ions can only
remove the fog of the latter kind by reducing the excess potential.
Benzotriazoles or other antifoggants may give you an impression that
they can reduce the fog of the former type, but it's because the other
aspects of development are also affected; if you develop long enough
to obtain comparable speed/contrast, the fog should come back. It's
more like reduced development rendering less fog (as well as less
speed, etc.). If you use radically large amount of antifoggants or
bromide, slightest emulsion fog may disappear, but at that point the
sensitometric curve shape is also altered.

> Increased
> Benzotriazole will tend to shift image color toward blue,
> Bromide toward yellow.

The hue shift with varying amount of bromide is not very systematic...
though benzotriazole almost always make the hue colder.

> Agfa makes a Phenidone-Ascorbic acid print developer, Neutol
> Plus. I don't have a formula for such a developer but I think Ryuji
> Suzuki has worked one out.

One difference I noticed between Neutol Plus and my formula is that NP
uses nitrilotriacetic acid (NTA) or something similar as the chelator,
while mine uses salicylic acid. NTA is a very good chelator for alkali
earth metals and transition metals, but I don't know how well NTA
works for the iron catalysis problem... (NTA is a famous builder in
laudry detergent that was developed to solve phosphate contaminating
lakes etc. but the US government basically told (or "asked") the
industry not to use it because it wasn't proven safe. The detergent
industry was of course very upset. It's now widely recognized to be
safe and commonly used in phosphate-free detergents. But in most
developed countries tertiary water treatment plants remove phosphates
before discharging the waste water, so phosphate-based detergents
don't make lakes dirty any more, except for some areas. I'm too young
to know the phosphate issue real time but I found the politics behind
this issue very intriguing.)

Anyway, I can get reasonably warmtone prints with phenidone-ascorbate
print developers.

--
Ryuji Suzuki
"All the truth in the world adds up to one big lie." (Bob Dylan 2000)