[pure-silver] Re: High B+F with DS-10
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 4 Feb 2005 12:09:48 -0800
----- Original Message -----
From: "Ryuji Suzuki" <rs@xxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, February 04, 2005 10:27 AM
Subject: [pure-silver] Re: High B+F with DS-10
> From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
> Subject: [pure-silver] Re: High B+F with DS-10
> Date: Fri, 4 Feb 2005 13:16:24 -0500
>
>> Most any ferricyanide, dichromate or
>> permanganate bleach can be used.
>
> Are you serious?
> How can I use ferricyanide bleach in reversal processing?
>
> I consider triacetate film base inferior to polyester base
> and I would avoid them as much as possible.
> --
> Ryuji Suzuki
> "Keep a good head and always carry a light camera."
Ferricyanide converts metallic silver back to a halide, or
at least a form which can then be removed by hypo. For B&W
reversal one must remove the original silver image without
affecting the remaining undeveloped halide. A dichromate or
Permanganate bleach will do this.
In color reversal it is not necessary to bleach the
negative silver image. The first developer is such that it
does not react with the color couplers to produce dye, the
reversal, or second developer is the one that generates the
dye. Since it works only on the halide remaining after the
first development a reversal color image is produced. A
bleach which removes the silver from the film without
affecting the dye is then used to clear the film. A
ferricyanide bleach can be used here. It is generally made
up into a sort of strong Farmer's reducer and called Blix,
or combined bleach-fix.
The thiocyanate or thiosulfate used in the first
developer removes very insensitive halide particles which
are not made developable by the original camera exposure. If
not removed these will remain in the highlight areas after
the first development and be developed during the second
development. The effect is to veil the highlights in the
reversed image. These particles are so insensitive that no
amount of overexposure of the original will cause them to be
developable. The addition of some halide solvent to the
first developer results in clear highlights and an increase
in the effective speed of the film as a reversal film.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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