laboratory negative

Darkroom Laboratory

Old Photochemistry


Darkroom laboratory guidelines


Nowadays, digital imaging is a constant in everyone’s live, either by digital cameras or by it’s constant integration in mobile devices and other products. Digital vastly surpasses analog photography in our days, mainly due to it’s extreme flexibility and capacity of “production”, bringing quick previews of the work being done and, vast editing possibilities that simply are not present in analog photography or not even possible.

Despite the range of options permitted by digital imagery, analog photography has always retained followers and lovers. The camera, the film, the printing, are all part of the seductive side of the analog photographic process that starts in the darkroom laboratory.
For some, camera gains the most attention, for me, it’s the process of bringing pictures to daylight trough a mostly “dark” process that always fascinated me and, leading me in a quest for always better processes to develop film.

For my analog photographs I use mostly stock film from Kodak, although my favorite brand was AGFA till the brand spin-off and halted film stock production. We can still find it today mainly because of the sublicences conceded to other brands.
As a purist and brand fan, AGFA terminated at that point.

Most of my processes were based in chemistry from AGFA, with existing pre made chemicals, so I started to look at the old formularies of the brand and, mixing back old formulations that I knew practically would pretty much remained the same throughout the years.

At this point I divide laboratory photo-chemicals and processes at this point in two groups, the main group, developers and, every other photo-chemicals from AGFA formulations and, a second group based on comercial preparations still available in the market. I will cover in more detail the developers bringing a centralized information on that subject.

Developer formulation has many different aspects to be considered and slight changes in a chemical can produce slight variations in the end result and as a consequence in the final print.

The role of different chemicals in the formula is approached briefly and it’s beyond scope of this site describing the different chemical reactions between the components of the developer with the negative but more detail are given on the actual impact of those components on the developed film.

I will focus on well established formulations, with proven results. Mainly because the easiness of preparation of the formulations but also one cannot expect exotic results when making slight changes to the components.

All the developers mentioned in specific pages are for black-and-white negative film development in laboratory.

Generic view of processing solutions :

The developer

Developers are essentially constituted by :

Reducing agent (the developing agent per-se)




Reducing agents  normally used are : Metol, Hydroquinone, Phenidone, 4-aminophenol, glycine, pyrogallol, cathecol and many others.

Preservative, the most widely used is sodium sulfite alone or with sodium bisulfite and included here also sequestrating agents like sodium EDTA to prevent calcium scum deposits.

Activators : sodium hydroxide, potassium hydroxide, sodium carbonate, borax, and others capable of creating a high pH.

The most used chemical restrainer is potassium bromide, in low percentages since the excess of potassium bromide in solution will restrain completely film development.

This is of course a general darkroom laboratory formulation,  the actual development of the latent image on the exposed film is in the majority of the cases confined to some basic conditions of the developer solution, conditions those I have mentioned before.

The vast majority of developers have alkaline pH, some with values as high as 12, exceptions exist in particular formulations where we can find slightly acidic conditions like for instance in the case of Amidol based developers.


The fixing agent

Fixing agents are responsible for removing the undeveloped, non-exposed and, insoluble silver bromide by converting it to the soluble silver thiosulfate.

By processing the film in the fixing bath, it makes it transparent where there is no image, but also makes the image permanent.

Composition of fixing baths are normally :

Sodium Thiosulfate (about 200gr)

Sodium Sulfite (15gr/L)

Acetic Acid (ca. 13ml /L)

Potassium Alum (as hardener)

pH =4,5


Formulation of fixing baths should observe some cares, acetic acid should not be added to plain thiosulfate solution since it decomposes the thiosulfate in a phenomenon called sulfurization.

The chemicals addition should therefore be followed as indicated.

Hardening agents like potassium aluminum sulfate should be used, negatives produced by the use of hardening fixing solutions are much more resistant than those processed in non-hardening fixing baths.

Optional laboratory processing solutions can be used, such as, stop-baths (with acidic value) to stop development immediately, and final washing aids like hypo-clearing solutions to remove any traces of thiosulfate remaining in the film.
Wetting agents can be used in a final wash to get uniform drying and with no water spots.

The overall developing process that I use can be resumed into defined steps:

Pre-wash / Pre-soak


Optional stoping bath





Final wash

Wetting agent bath

After completion of the developing process, the film is set to dry in a dust-free environment until completely dry.

The process itself will be covered in more detail in dedicated pages.

Consistence is a key factor for good film development and it must be always present if one is achieving good results with classic film development.
There are elements that are difficult to control and have direct influence on the final results, like precise temperatures of working solutions, pH, exhaustion of baths and agitation.

Care should therefore be taken to ensure that all processes are made consistently.