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In my black and white photography class, the teacher recommends us to use ISO 400 to develop our film and make prints. I found that ISO 400 is much too grainy for my liking, and as a result I want to move down to something like ISO 100 or ISO 200.

My question is, does this affect at all the development and printing processes? Can I still use the same materials to develop, for the same amount of time as the ISO 400 film (like wise for the printing)?

I am using Ilford HP5 ISO 400, I want to use Ilford ISO 100

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For the most part, all the chemicals of the black & white process are compatible. A 400 speed film, in my opinion, is not all that “grainy”. That being said; if giant prints are the goal, then use 200 or better 100 ISO. This is because slower films contain less silver. The grain you see is a clumping of metallic silver in the emulsion. A 400 speed film developed in a fine-grain developer does quite well.

A fine grain developer likely contains a mild silver solvent that reduced grain size by dissolving away some of the silver clumps. One trick of the fine grain developer is to stain the image giving it a slightly warm tone. The warm tone allows reduced developing time while retaining printing density. An olive tone acts to filter out some blue and UV light. This makes up for the lower silver content. In other words, the negative has a higher printing density despite the fact that the metallic silver image is abridged. The result is reduced apparent grain.

  • > slower films contain less silver -- that would be an overgeneralization. – Iliah Borg Oct 28 '15 at 21:52
  • Slower films have less silver is a truism. T-grain was a Kodak discovery. Silver salt crystals can have trace amounts of gold or cadmium added and this plus proprietary stuff yields a crystal that is flat like a stepping stone. Orientate the flat surface towards the lens and you get more sensitized surface with less silver mass. Remember grain is the clumping of metallic silver and not an individual flake of metallic silver. – Alan Marcus Oct 28 '15 at 23:41
  • if you want to know why it is an overgeneralization please post a question. – Iliah Borg Oct 28 '15 at 23:56
  • Kodak aim points per 1000 sq. ft. material 32 ISO = 7.3 Troy oz. 125 ISO = 10.4 T ox. 320/400 ISO = 15.6 1250 ISO = 26.4 ISO – Alan Marcus Oct 29 '15 at 3:04
  • Does not work cross-brands and cross-emulsions, KODAK ROYAL GOLD 100 17 tr. oz./1000 sq.; KODAK GOLD 200 16 tr. oz./1000 sq. ft. I also wonder why you mentioned T-grain while the film in the OP is Ilford, and even not a Delta - it is "cubic grain". The Kodak's classic "The higher the Silver, the higher the speed, contrast and the lower the grain. Sharpness goes down as Silver goes up" - does not apply universally in reverse. While "more silver, more speed" is correct when you are developing an emulsion, "less silver, less speed" is not always correct comparing emulsions. – Iliah Borg Oct 29 '15 at 12:09
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To expand a bit on the comment by @Iliah Borg:
Typically, the chemicals you use are not bound to the film speed they're developing. The film speed determines the time that the film needs to rest in the chemical during development. This can also be used to push or pull a film that you deliberately under- or overexpose throughout the whole roll of film (again, this does not change the sensitivity of the film, but the gradation of the result).
Another factor in the development calculation is the developers concentration and the temperature of the chemical. You will have to put all these into consideration of the development time. This is where the development time table (which includes the film model/ISO) comes into play that has been mentioned by Iliah.

I recommend you read through his linked file.

What does influence the development and the chemical you use is the type of crystals your film uses and the type of grain you want to achieve. Read on T-crystals and connected developers for modern fine grain.
For a more technical information you can start on wikipedia
https://en.wikipedia.org/wiki/Tabular-grain_film
a discussion about classic vs modern film emulsion can be found here
http://photo.net/black-and-white-photo-film-processing-forum/00ERvk

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