How can you control contrast in black and white film development?
 Micron
Answer 2Since the question was about film contrast and not photo contrast, my comments pertain to step 1. The best way to control contrast is by matching the characteristics of the film with those of the developer, and modifying exposure to suit. Sounds vague because the answer is not as simple as suggested, and really requires a good knowledge of film and developer characteristics (which can be learned from books). Simply modifying development time is a less than ideal approach since that will affect the amount of silver halide that has been converted to black metallic silver (BMS) OVERALL, primarily affecting the image density and therefore, quality. Yes, the highlights will be slightly more affected than the shadows, hence a minor variation in contrast. To the critical eye, the result will likely be somewhat dissapointing, and in the case of increased development, may result in image fog (indiscriminate addition of BMS over the whole image). The best approach is to select a developer with the characteristics (more/less metol, hydroquinone, bromine [or is it bromide, I forget]) suited to your particular need. Read the product sheets or library books to learn more.Here is a technique that I learned 20 years ago for high contrast scenes (streetscapes/store fronts with night lighting, etc.) that produced some amazing results.1)Over-expose the film by 3 stops to produce extra shadow density (two would ordinarily suffice, but I went the extra to allow for reciprocity failure due to long exposure times).2) In total darkness with one open tank of regular developer and one open tank with water, using a reel with a spool center, lower the reel in the developer, rotate reel for 10 seconds to prevent air bubble adhesion & let sit for another 50 secs.3) transfer to the water bath for 4 minutes, NO AGITATION.4) transfer back to the developer, gently agitate (by rotating spool) for 10 secs., total immersion to be 1 minute.5) Repeat 3 and 4 so that the entire cycle is 1-4-1-4-1-4-1 = 16 minutes to develop.6) Stop and fix as normalHOW DOES THIS WORK??Each immersion in the developer does the usual thing. The water bath causes development to rapidly slow down in the highlights due to the levels of bromine (see above) being produced as a by-product of reduction (silver halide being reduced to BMS). However, the bromine levels in the shadows are less because the amount of BMS produced is less, hence the water has less effect. Since the film was much over exposed, the shadows will produce more density while the highlights are suppressed. I have produced B&W prints from such negatives on Ilford Multi-Grade paper with no contrast filters with detail in the shadows (showing bushes) and no burning-in required during printing for the lights on or in the builidng. The technique seems to enhance the acutance of the BMS as well, producing very sharp definition. BTW, I also learned how to reduce the contrast of color slides using a Freeman Patterson trick. If y'all would like to converse on this, I can be reached at yullneverknow.com (I only access this once every month or so, so be patient initially).By now you may have surmised that I got real heavy into the science of development at one time, and hopefully was able to spark some interest in my students.Micron************************* Answer There are essentially three basic ways to do it.First step is when you develop the film in the film tank with the developer. Developing times are put out by the film makers for optimum exposure representation. So if you want absolute control over your pictures, use these times. If you want to get a bit uncontrolled (crazy), try leaving the developer in for another minute or so, or take it out a minute early. The longer you leave it in the more the contrast, while the shorter its in the more gray you get. This is quite a random process, because as soon as you disregard the manufacturers recommended times, the film can behave in ways beyond your control, due to room temperature, water acid levels, and if you live in Auckland especially, the amount of fluoride in the tap water.Second, if you have a black and white enlarger (ie. there aren't colour control adjusters) you will need filters. You can buy these singularly, or in packs. I suggest the Ilford Filter pack, as this gives you a good range of filters. They come in grades, from 00 to 5, with half increments in between, the 00 give the least contrast, while the 5 gives the most. Depending on your enlarger, put a filter in above the light box. Some enlargers have the slot under the light box, so look out for a holder approximately the same size as your filter. When exposed, the light passes through the filter, with certain frequencies getting knocked out or converted, so the light hitting the photo paper is controlled to give a certain amount of contrast.The third common method gives you the greatest control over the amount of contrast, and is my preferred method. If you are lucky enough to have access to a colour enlarger, use it, even for black and white photography. Set all the dials onto 0, except for the Magenta, which you set to about 60. This gives you approximately the same amount of contrast as on a standard black and white enlarger. To get more, increase the magenta, and to get less contrast, decrease the magenta. From there, develop your paper as a normal black and white print.I have on one occasion required more contrast than the magenta dial could give me. To counter this, I squeezed a contrast filter into the machine above the light box. If you do this, ensure you have a foolproof way of removing it.Remember that as soon as you start using filters, you are cutting down on the amount of light that is getting to the paper. You will need to increase exposure time in the darkroom to compensate for this.