Basics of a developer

Now that I have started to mix my own developers from scratch I have become curious as to what the function is of the various components.

As an example, here is a very basic developer.

The Barry Thornton's 2-Bath

Bath A
Metol 6.25g
Sodium Sulphite 85.0g
Water to 1 litre

Bath B
Sodium Metaborate 12g
Water to 1 litre

You probably can't make a simpler formula, so I assume these 3 components comprise the basic buiding blocks of most developers.

Can someone explain what the function is of the individual chemicals?


thanks

HL

Buy Steve Anchell's 3rd Edition of The darkroom Cookbook

Metol - developing agent

Sodium sulphite - preservative, helps prevent developer oxidation, also mild silver solvent

Sodium Metaborate - buffered alkali - basically Borax & Sodium Hydroxide, alkali is needed as an accelerator for the developing agent, makes it work faster.

Water, my father always said best only drunk in whisky

Ian

Harry Lime said:

As an example, here is a very basic developer.
The Barry Thornton's 2-Bath

Bath A
Metol 6.25g
Sodium Sulphite 85.0g
Water to 1 litre

Bath B
Sodium Metaborate 12g
Water to 1 litre

You probably can't make a simpler formula, so I assume
these 3 components comprise the basic buiding blocks of
most developers. Can someone explain what the function
is of the individual chemicals? thanks HL

Click to expand...

Odd you should pick a two bath to be the most simple
of formulas. Actually that A bath represents the most
simple of formulas. That formula is a variation on
D-23, a very popular developer.

I believe sodium ascorbate and metol or phenidone
may also form two component developers. The two
chemicals in each developer are the developing
agents themselfs and the preservative/
accelerator. Dan

Thanks Ian.

In addition to the Sodium sulphite, does the methol also act as the main silver solvent?
If I adjust it's amount, will I end up with softer / sharper grain?

thanks

The Metol is reducing the exposed silver halide to Silver, so no it's making the grain insoluble.

Metol is soft working anyway so in a two bath developer altering the amount is likely to effect density & contrast rather than grain. nMore metol, drops contrast but increases density & vice versa.

Ian

No, the sulfite is acting as the silver solvent, but how much of a solvent it is depends on the total amount of sulfite in the working solution. This is why D-76 straight is a solvent developer, but D-76 1+3 starts to produce results more like an acutance developer. So if you wanted to get sharper grain with this developer, you could reduce the sulfite, but really, you might be better off using a different developer or experimenting a bit and try making a metol-hydroquinone version of this developer, because metol is kind of a soft working developing agent compared to other developing agents.

[edit: Ian's typing faster than I am this morning.]

Harry

You've chosen a developer that has some rather complex interactions,
and it might be hard to determing what is happening, and why.

A more clear cut developer might be something like this, circa 1920

AGFA #1
Metol 15 grams
Sulfite 75 grams
Potassium Carbonate 75 grams
Potassium Bromide 2 grams

Dilution 1+4 ~ 1+15.

Here, you'll see that Metol can certainly give a full toned negative;
you'll be able to explore the relationship of pH & Sulfite to acutance and fine grain.

By the end of the '30s, several lines of investigation lead to high Sulfite Developers like D-23, which could be 'interpreted' by the user to fine tune their lab work. In many ways, D-23 (and other similar formula which had, umm, inspired Kodak's research) represent a jumping off point for most of the commonly known developers today.

Thornton's 2 bath is an example of how a traditional formula does not have to be conventional, for Thornton saw how he could make minute variations in the recipe to suit his particular needs.

By all means let Troop guide you in "The Cookbook"
and have fun.

d

Ian Grant said:

Water, my father always said best only drunk in whisky

Ian

Click to expand...

Ian - what a wise man your father was

Martin

Thank you for all the information, gents.

I most certainly need to get hold of a copy of the Darkroom Cookbook.


HL

Sodium Sulfite is also a mild alkali, which is why D-23 can work with just water, metol and sulfite.

You need, for a working developer, at bare minimum: developing agent, preservative, and accelerator.

Metol is the "developing agent", and like all common developing agents (save amidol*), requires alkalinity to work. The developing agent does the job of turning exposed halides into metalic silver.

Sulfite acts, as it does in almost all developer formulas, as "preservative" so as to keep the developing agent functioning. I gather sulfite scavenges up oxygen before the oxygen can wreck the developing agent.

Sulfite also, in this case is the "accelerator" - using it's mild alkalinity to create a gentle developer.

In the case of the original two bath formula you presented, the sodium metaborate serves as a stronger accelerator so film will more quickly finish development using the metol "stored" in the film itself. Kind of a neat trick, since the development exhausts early in the highlights by using up the developer, but keeps on working in the shadows to give them fuller development. A self adjusting development process; sort of self masking.

Many more muscular formulas will also have a "restrainer" to keep fogging in check. D-23 avoids that by not being so vigorous as to produce much development of unexposed silver.

*amidol can work without alkalinity - I know not why. PE????

Best,

C

The Darkroom Cookbook is a wonderful broad brush primer to do it yourself mixing of photographic formulae. The Film Developing Cookbook drills down into finer detail of what makes various developers behave the way they do. Get the Darkroom Cookbook first, but you may very well find the second a great compliment to it.

C

Thanks again, guys.

Developers belong to a class of chemicals called reducing agents. Simply, these change salts into their respective parts so Silver Halide + reducing agent = oxidzed reducing agent + Silver metal + Halide. A good developer does this imagewise, but a strong reducing agent just gives total fog.

Reducing agents are classed by their "reduction potential" and reduction potential is a function of pH. Amidol functions over a wider pH range than most developers, but this has a down side. Amidol developers stain and go bad very quickly. Most developers act more strongly at high pH and give more contrast. At very high pH, some fog emulsions. Some are quite active down to low pH and are stable, unlike Amidol. Amidol, due to its very nature, decomposes when it oxidizes.

There you have a summary of developers in a very simplified form.

Both Mees and James, and Haist have extensive lists of developing agents and their reduction potentials along with activity profiles as a function of pH. They also give excellent outlines of the basic theory of developer design.

PE

An Overlooked Source of Information

Ed Buffaloe's Unblinking Eye has been updated.
www.unblinkingeye.com

From Ed and many other contributors there is treated a
VAST number of subjects related to darkroom processes.
That includes the very basics of the chemistry involved
and the part each plays. Explore the site.

For the basics click on Articles at the bottom of the home
page then look for, mixing developers . Included there are
the low downs on several developing agents, preservatives,
accelerators, and restrainers. Dan