[pure-silver] Re: 'Ripening' procedure for developer?
- From: titrisol <titrisol@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 4 May 2007 04:37:29 -0700 (PDT)
I would believe that plastic "jars" will have shorter life than
tin cans, but maybe in the same order of magnitude than
foil/paper
Plastic, depending on material, method of production, etc will
have a lot higher permeability to oxygen/water than tin cans.
The problem with foil/paper, that plagues food packaging as
well, is the permeability to air of the pacakging.It was
supposed to be nearly nil but since the foil is so thin and it
is sandwiched between layers of polyehtylen/paper it is not so
impervious as originally thought. Tetrapak type containers do a
great job, but I do not thing that combo would be economical for
dry powders.
--- Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote:
>
> ----- Original Message -----
> From: "Jeffery Smith" <jls@xxxxxxxxxx>
> To: <pure-silver@xxxxxxxxxxxxx>
> Sent: Thursday, May 03, 2007 6:29 PM
> Subject: [pure-silver] Re: 'Ripening' procedure for
> developer?
>
>
> Developers like D76 change for the worse over time. One of
> the problems is
> pH change, which affects the activity of the developing
> agent. I have been
> using divided D76, which is a bit more stable. The first
> bath allows
> inactive developer to soak into the emulsion. Time and temp
> aren't
> important. Transferred to the alkaline bath (borax), the
> developer in the
> gelatin becomes active until it is exhausted. The first bath
> can be reused
> over and over. The 2nd bath (cheap) is discarded.
>
> But I am getting to the point that I don't trust developer
> unless it is
> fresh. I have bought about 5 kits of Paterson citric acid
> developer. By the
> time it reaches the states and gets into my darkroom, it is
> DOA.
>
> Jeffery Smith
> New Orleans, LA
> http://www.400tx.com
> http://400tx.blogspot.com/
>
> D-76 is an interesting case. Shortly after the formula
> was released in 1927 it was discovered that its activity
> increased slowly. The real cause took decades to discover
> but the immediate cause was a rise in pH. In 1929 a research
> paper was published by Kodak Research Labs describing the
> problem and a solution for it along with data on a great
> many variations of the formula. The cure was to buffer the
> solution by using a combination of Borax and Boric acid. The
> data in the paper shows the the developement time for the
> original formula for a given gamma was reduced to a bit more
> than half the time after storage for about a month. For the
> buffered version there was insignificant change over the
> same period.
> It was discovered much later that the mechanism for the
> pH rise was a slow reaction between the Hydroquinone and the
> Sulfite which produces a small amount of Sodium Hydroxide.
> Developers which do not contain Hydroquinone do not suffer
> from this problem. It is likely that the pH of many M-H
> developers are high enough to begin with that the small rise
> from this reaction is of no significance.
> The packaged version of D-76 has been the buffered type
> for several decades. For those interested the formulas are
> as foll
>
> Standard D-76
> Water (at 125F or 52C) 760.0 ml
> Metol 2.0 grams
> Sodium Sulfite, dessicated 100.0 grams
> Hydroquinone 5.0 grams
> Borax 2.0 grams
> Water to make 1.0 liter
>
> D-76d
> Water (at 125F or 52C) 750.0 ml
> Metol 2.0 grams
> Sodium Sulfite, dessicated 100.0 grams
> Hydroquinone 5.0 grams
> Borax 8.0 grams
> Boric Acid, Crystaline 8.0 grams
> Water to make 1.0 liter
>
> This will have the same activity as the original formula
> when fresh.
>
> The activity of the buffered developer can be varied over a
> wide range by changing the relative amounts of Borax and
> Boric Acid.
> Crystaline Boric Acid should be used because the granulated
> variety dissolves with great difficulty.
>
> A note about packaged Kodak products: Kodak has a
> large number of patents for the stabilization of the
> ingredients of both powder and liquid developers and other
> chemistry. They also seem to have paid a lot of attention
> over the years to sequestering agents, etc., to make their
> packaged chemistry as nearly immune to water quality as
> possible. No doubt other manufacturers have done the same.
> Other than a couple of bad experiences with Xtol I have
> never had a failure with any packaged Kodak product. There
> is a limit of lifetime to the materials in the paper
> packets. The packages are made of a paper lined with
> metalized plastic. They were supposed to be completely
> impervious to air and moisture but obviously are not. I
> don't know the mechanism of the failure but suspect it is
> micro-cracks in the metalized plastic liner. In any case,
> I've opened very old packages of Dektol which looked like
> coffee grounds and smelled like dead mice. Not nice. The
> very old stuff in hermetically sealed tin cans seems to last
> forever. A couple of years ago Kodak got rid of the paper
> packages in favor of all plastic ones with one less seal.
> Its too soon to know how well these hold up for long time
> periods.
> Some liquid concentrates do not have unlimited life.
> For instance, rapid fixer will eventually decompose. Again,
> I don't know the mechanism but it may be due to leakage of
> air through the plastic containers and is at least partly
> due to the inherent instability of the chemicals although
> they are treated to improve their stability.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
>
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