Re: direct positive

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From: Tadeuz Jalocha (tjalocha@netexpress.cl)
Date: 11/22/00-06:33:55 AM Z


Hello,

Exactly i had a idea in the same direction tonight. There some chromium
intensifiers who count on this stain to produce the wanted
intensification. And these intensifiers even work on film...
The big difference seems to be the light. If you use bright light while
you bleach, you get stain. I only use light for the second exposure. The
rest of the process is done in very dim safety light.

Hope this eliminates thes stain.

Tadeuz

"Vrueh, G.J. de" wrote:
>
> Hello Liam,
>
> This is not the awnser to your problem but yust some thougts going trough my
> mind...............
>
> I have had a simular experience in the past with another proces, namely with
> oil printing.
> Without discribing the whole proces what happens is as follows: after
> applying a thick caot of gelatin to paper and drying the paper is coated
> with a amm bichromate, dried and exposed to uv though a large negative.
> After exposure the paper is washed, cleared with metabisulfiet washed and
> dried.
> After this the paper can be made wet again and the gelatin matrix can be
> inked.
>
> After washing i always noticed that there remains a ghost image very light
> brownish-grey. This ghost image does not disapear after clearing. It
> appeared to me the stain is most appearend were exposure was greatest.
> This looks like your problem is such an extend that there where the bleach
> works the most (ie where the most silver is removed, the highlights to be)
> the stain is most apperent.
>
> In the process of oilprint the galatin is chemically bonded (tanning) by the
> bichomate under the influence of UV. I think this also happens when you
> bleach(in fact bromoil printing works with this phenomenon. there is also a
> ghost image in this proces)). This means that the gelatine hardens and is
> harder to clear at that point. Maybe a by product is formed during this
> reaction that causes the stain.
>
> I think it is not the support that causes the problem but the thikness of
> the gelatine. Altought i have to admit that i do not know weather or not PE
> paper has a thinner galatin caoting than FB paper and so i cannot explain wy
> PE paper does not have this problem.
>
> Isn't there a bleach with non hardening properties but one thas does solve
> the silver image?
>
> Greetings Gerard de Vrueh
>
> -----Oorspronkelijk bericht-----
> Van: Liam Lawless [mailto:lawless@ic24.net]
> Verzonden: woensdag 22 november 2000 5:05
> Aan: alt-photo-process-l@skyway.usask.ca
> Onderwerp: Re: direct positive
>
> Hi Taduez,
>
> That was meant to be a private message to Judy and I wasn't aware it had
> gone to the list. Sorry everyone!
>
> However, I get staining - grey-brown in what should be the white tones - on
> Ilford Warmtone, fibre-base - perhaps plastic papers are OK, but I don't use
> them! What I'm trying to do is get reversed prints, not so much for use as
> paper negs, but as final images - on Ilford WT FB if possible. My
> "brilliant idea" did not work as well as hoped, but I'm also exploring other
> avenues.
>
> So, I suspect that dichromate bleach is incompatible with WT FB, and maybe
> all fibre base papers. But your remark about omitting the clearing bath is
> interesting, and may persuade me to buy some Ilfospeed.
>
> Thanks for your input.
>
> Liam


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