water pre-soakgreenspun.com : LUSENET : B&W Photo - Film & Processing : One Thread
Some recommend that film have a water presoak before the film developer. I usually have not done this, but thought Id try it. It makes sense, it allows the developer to contact "wet" film and may give a smoother pour-in without any streaking. So, I tryed it this weekend, and was surprised to see the water pre-soak was green when I dumped it. Any ideas why it would be green?
-- Mark (firstname.lastname@example.org), August 21, 2001
The color is sensitizing dye. It's normal, and usually washed out by usual chemical process, from developer to final wash.
The main cause of streaking is not the dry film and developer interaction. It is often said that today's films have reagents in emulsion so that the interaction between dry film surface and developer starts up uniformly. Presoak is therefore said to be not beneficial, and manufacturers tend not to recommend it. It is also often said that developing time needs adjustment when film is presoaked. However, I have not seen any convincing data that support these statements, although I have no reason to disbelieve these statements. I do not presoak.
Anyone measured exposure-density curve at a fixed developing time with and without presoak?
-- Ryuji Suzuki (email@example.com), August 21, 2001.
Photo Techniques magazine published an article by Phil Davis on presoaks a couple of years ago.
To sum it up, Phil's findings were that a long presoak caused variations of EI and CI that differed according to brand and type of film while a short (one minute) presoak caused negligible changes.
Ilford recommends against using a presoak, stating that it would wash out the wetting agents in the emulsion, perhaps unevenly, and that could cause uneven development.
My experience is that there's no justification in using a long presoak while a short presoak will prevent airbells in rotary processing and doesn't cause any unexpected development variations or unevenness.
-- John Hicks (firstname.lastname@example.org), August 21, 2001.
As John stated, the article that he mentions was a great one with alot of plotted graphs showing the large differences with presoaking. My recommendation would be to presoak for 15 seconds (with a drop of LFN) just so there would be a smooth transition into the developer. If you aren't having trouble with airbells and your development is fine... your need to presoak isn't needed!
-- Scott Walton (email@example.com), August 26, 2001.
My main reason for pre-soaking is temperature balancing of the development tank and film.
I have several times noted that if I pour in 20°C water in the tank, agitate the tank and measure the temperature it might have changed to 18.5 or 21.5 degrees, although the ambient temperature is kept between 17 and 24 degrees. This will of course influence the development if no pre-soak is used.
I am using plastic Paterson tanks, and always pre-soak to get the tank and film adjusted to 20°C.
-- Anders Blomqvist (FIN) (firstname.lastname@example.org), August 27, 2001.
I do not know which film you used, but you obviously got the antihalation backing in the presoak. Some films rely on this to prevent light spreading through the emulsion, if the manufacturer does not use a pronounced gray base. Without these measures you would have decreased sharpness and accutance. Some films have huge problems with light spreading through the emulsion, as can be seen with TMAX 100. Its immense fuzzines obviously is based on "light piping". An exposed silver halide passes the light information on to the halides around it, thus decreasing sharpness, resolution and accutance. While Ilford trusts the gray base, Kodak seems to prefer the antihalation backing. Also Efke has one. The Efke one is green for expample. It is necessary that this backing disolves during development, otherwise you would have a semi transparent film. These backings are water soluble and first traces will be seen in the presoak. The green colour will not affect development in any way.
-- Volker Schier (Volker.Schier@fen-net.de), August 31, 2001.