Photographer's Formulary Prescysol is a specially formulated developer unsurpassed in its ability to provide superb negatives with extremely fine grain, remarkably high sharpness, smoothly gradated tones and delicate and translucent highlights. Prescysol yields full film speed; you can expose at the makers recommended ISO.
Tanning and staining developer
As the developer is absorbed, the emulsion is tanned, or hardened, and this hardening is variable, being greater in areas of greater exposure; As the emulsion tans, it inhibits the absorption of further amounts of the developing agent, and so development in these highlight areas is restrained; The lower tanning action in the shadow areas allows development to continue and these areas continue to build, producing negatives with rich, deep shadows, beautifully gradated mid-tones, and delicate highlights
Negatives developed in Prescysol particularly using the partial stand method, will yield full speed, exhibit high acutance, and will need considerably less burning-in to areas such as skies
As development proceeds, oxidation and natural by-products of the process stain the emulsion brown, the staining being proportional to the exposure level of the various parts of the negative; The result is a continuously-variable mask of printing density across the tonal range of the negative
As the emulsion is stained mostly between the silver grains the effect is to soften the grain and so produce a smoother tonality in large areas such as sky and mist, where grain can normally be such a problem
Prescysol is an extremely tolerant developer; films of different make and speed can be developed together at the same time. For example, HP5 400 (120 roll film) and Delta 100 (35mm) despite being of totally different grain structure, can be developed together in the same tank for the same time
In fact, the modern tabular grain films (which require closer control of times and temperatures in normal developers and are more susceptible to burned highlights and blocked shadows) will benefit enormously from being developed in Prescysol yielding the fine grain, tone and acutance of which these films are capable