by Ed Buffaloe
Development by inspection is not much practiced anymore, having been largely supplanted by time and temperature development, which is considered more scientific, more precise, more repeatable. The move away from inspection was necessitated by the ever-increasing speeds of modern emulsions and more particularly by the trend toward small roll-film negatives. In the earliest days, very slow monochromatic emulsions (sensitive only to blue light) were routinely developed under a yellow safelight. In an era when timers were luxuries rather than necessities, development was stopped when shadow densities were judged adequate, and it was even possible to manipulate development by utilizing water baths, during which one could apply developer to specific areas needing more development or bromide to areas needing greater restraint.
As plates and films became more sensitive (orthochromatic emulsions are sensitive to green as well as blue light), ruby safelight filters became necessary, but the old manipulation techniques could still be utilized. With the introduction of the yet more sensitive panchromatic emulsions, however, dark green filters were required, inspection times could last only a few seconds, and inspection could not begin until development was at least half complete. This made the process somewhat more uncertain, as one could no longer watch the entire development unfold. Water-bath development and other negative manipulations became much less practicable.
Development by inspection is particularly useful to large format enthusiasts. Inspection can help determine the correct development time for new materials, and when used intelligently can help one achieve success with difficult exposures. Since every scene is unique, with difffering levels of local as well as overall contrast, customized development of each scene ultimately gives the best results. Small format roll films are almost impossible to judge by inspection, and medium format inspection is difficult at best.
The primary requisite for inspecting panchromatic film is a dark green safelight filter. Still available are the Kodak #3 and the Ilford 908 filters, although they will likely have to be special-ordered. A 15 watt light bulb at 4 feet is the standard recommendation. Under "normal" circumstances, the negative should be developed for at least two-thirds the "normal" time before inspection, though allowances may be made for negatives that are known to be overexposed. As development progresses, the negative becomes increasingly desensitized to further exposure, but it is always advisable to keep inspection times to a minimum.
To learn how to judge negatives, one should begin with a normally exposed negative (i.e., one not requiring plus or minus development) and use a film and developer combination for which one has known accurate time and temperature information. Develop the film for the correct time, place it in a water bath to halt development, and examine it carefully under reflected light. First of all, the emulsion side will be mostly dark. Therefore, one should closely examine the base side of the negative. The base will appear milky, but zones VIII and above (the high values of the scene) will be distinctly black, and there may be some detail visible in zones VI and VII. The important point is to pay attention to what your correctly exposed and developed negatives look like, so you can recognize correct development when the need arises. After a brief examination, turn off the safelight and stop and fix the negatives as usual. Later, you should examine high-contrast and low-contrast negatives for comparison purposes.
One generally wishes to avoid overdeveloping the negative, but the consequences of underdevelopment are much worse. Since the shadow areas are difficult to judge by inspection, one is primarily left with the option of preventing underdevelopment by examining the high values. You should pull the negative from the developer when the highlights appear as substantial black in the general milkiness of the base side. This is the gist of the technique. If the adage "expose for the shadows and develop for the highlights" has been followed correctly, and you have photographed a subject with a normal brightness range, when the highlights appear as substantial black on the base side, the negative will be sufficiently developed. To guard against overdevelopment, you simply have to learn not to allow the high values to get too dark. Experience is the best (and only) teacher.
These instructions are for negatives to be printed on silver-gelatine papers--most alternative processes require greater contrast.
Push and pull processing is sometimes better done by the time and temperature method. If the negative is of a very low contrast subject (or if it is a copy negative), you may not be able to see much in the way of highlight values on the base side, even when overdeveloped, so time and temperature may be your only salvation. It is, however, possible to examine the negative by transmitted light, placing a finger behind the negative to provide a dark object with which to compare highlights. The highlight values (dark portions of the negative) should be distinct from and not as dark as the total darkness of your finger. It requires considerable experience to judge a negative in this way.
Negatives of very high contrast subjects present unique difficulties, since they often show highlight detail on the base side early, but may require further development to provide sufficient shadow detail.
To salvage a negative that has been severely overexposed, it should be pulled from the developer just before highlights appear on the base side (in other words, it should be under-developed), in order to maintain a printable density range. There is no avoiding the fact that some scenes do not present enough contrast (either overall contrast or critical local contrast) to be easily judged by inspection, so it is important to take two shots of every scene, where possible.
Negatives developed in pyrogallol or pyrocatechin are particularly suitable for development by inspection—the tanning effect these developing agents have on photographic emulsions desensitizes them somewhat to further exposure. Because pyro negatives have less silver density than normal negatives (the balance being made up by stain), more detail is visible and they are somewhat easier to judge.