[pure-silver] Re: really pink negatives mystery solved
- From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 15 May 2009 23:25:39 -0700 (GMT-07:00)
-----Original Message-----
>From: janet ness <nessj@xxxxxxx>
>Sent: May 15, 2009 10:04 PM
>To: pure-silver <pure-silver@xxxxxxxxxxxxx>
>Subject: [pure-silver] really pink negatives mystery solved
>
>
>I had recently posted a message about film developed by students in my class.
>The negatives were developed in Xtol and came out magenta colored. It turns
>out that both rolls were chromagenic black and white. One was Ilford XP-2. I
>didn't think you could get anything by developing this film in black and white
>chemistry. The images look like they could be printable, though the color of
>the film base could affect the contrast.
>
>Janet Ness
>
All color film is really silver B&W film in disguise. The difference
between a monochrome film like XP-2 and a full color film is that XP-2 has only
one emulsion layer (well it might have more than one). Color film has one or
more layers for each primary color. Each layer contains chemicals called "color
couplers" which react with certain developers to produce appropriately colored
dyes. In XP-2 the dye or probably a combination of dyes are neutral gray. The
developer produces a conventional silver image and the dyes are produced in
turn by the reaction products of this development so they are proportional to
the silver image. After development the silver image is bleached out leaving
only the dyes in the emulsion. A similar process, with more steps, is used for
reversed images but, again, the developers produce conventional silver images
and the dyes are generated as a side effect of development.
Usually, when a chromogenic monochrome film is developed in a non-reactive
developer the resultant silver image may be a bit weak or may be grainier than
the dye image would have been since the emulsion is not designed to make a good
image directly but rather to work with the developer to make dyes.
Normal color negative film has couplers which are themselves colored. When
developed normally these act as a mask to correct for imperfections in the dye
absorption. The couplers usually have a yellowish color. This disappears where
the coupler is converted to dye but remains elsewhere. If the couplers are not
converted to dye the color remains throughout. This is why color negative film
appears to be orange colored. I don't know what is in XP-2 that results in a
pink color. Some chromogenic monochrome films have a dye which simulates the
masking color in standard color negative films in order to print neutral on
standard color paper. I think XP-2 is intended to print on normal B&W paper so
doesn't have the masking color.
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
Los Angeles, CA, USA
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