[Alt-photo] Re: DAS

[Marek Matusz]

All,
I have purchased some DAS for carbon work. I just made my first tissue and test prints with a step tablet. I will scan and post them later, but I noticed an non-liner response of the tissue to the light. In the highlights I get no exposure and my first visible step is already way dark. It is easier to describe with the picture. My prints are drying and I will scan and post them later.
 
Does anybody have step tablet tests of DAS sensitized carbon to share?
 
Marek
 

> Date: Thu, 25 Apr 2013 18:53:03 -0400
> To: alt-photo-process-list at lists.altphotolist.org
> From: pfriedrichsen at sympatico.ca
> Subject: [Alt-photo] Re: DAS
> 
> Hi Charles.
> 
> These are fluorescent lamps and are of the "black light blue" 
> variety, so they have a violet woods glass that blocks most of the 
> visible rays. The glass also blocks out shorter wavelengths from what 
> I understand. The peak is actually a bit higher than I mentioned, at 
> 369 nm with a peak width of about 16 nm. There are a couple very 
> small peaks in the blue, and another small one in green (mercury 
> line) but they account for very little of the total energy emitted.
> 
> As you say, different wavelengths may penetrate to different depths. 
> It may be that blue or green light may penetrate further but surely a 
> longer exposure as a trade off.
> 
> One of these days I will have to try exposing this DAS with white 
> light under a spectrometer, one I built some years ago. It is a 
> matter of dusting off a dinosaur laptop since it won't run on modern 
> OS's because it interfaces with a parallel port. The limitation is it 
> doesn't go below 350 nm.
> 
> Peter
> 
> At 02:03 AM 25/04/2013, you wrote:
> >Hello Peter,
> >
> >Thank you for this valuable information. It illustrates a great deal about
> >the penetration of UV light into a sensitized emulsion and accounts for
> >differences in exposure "speeds".
> >
> >Do you know what type of lamp was used to exposure the tests?
> >Multi-spectral lamps (Metal Halide/Mercury Vapor) emit varying wavelengths
> >of varying intensities (% of emitted light). A Series 0 lamp, for example,
> >which is used for most platemaking applications, emits 0% at 320 -360 NM
> >(DAS peak sensitivity is 335NM) while 11% of a Series 7 bulb is in the 320
> >- 360NM spectrum. Both lamps, of course, emit large amounts at 365nm, but
> >comparisons of emitted light absorptions may be affected by the secondary
> >wavelength outputs of the lamp.
> >
> >In any case, it does underscore the need to find an exposure bulb that
> >matches the specific spectral sensitivity of the materials for maximum
> >penetration and minimum exposure.
> >
> >Charles
> >
> >
> >On Tue, Apr 23, 2013 at 12:35 AM, Kees Brandenburg
> ><workshops at polychrome.nl>wrote:
> >
> > > Hi Peter,
> > >
> > > That's very interesting information and completely in line with my
> > > observations. This also strengthens my hypothesis that ferric carbon is the
> > > absolutely winner concerning relief. It's also in line with Charles remarks
> > > about DAS sensitized tissue gelatin thickness optimization. The DAS
> > > sensitized tissue that printed best for me is a #200 coating rod coated
> > > tissue with relatively much pigment.
> > >
> > > The lower pigmented, hand coated 1 mm wet height tissue printed much
> > > softer, with less dmax and the relief was stil almost absent. The heavy
> > > selfmasking lengthens the tonal scale significantly but also prevented
> > > digging deep in the layer. With this tissue though it's very nice printing
> > > in 2 or 3 layers with different exposure times!
> > >
> > >
> > > I will do some more tests with a #90 rod, I don't have the #120 Charles
> > > mentioned. Also cutting down Gelatin/DAS ratio might bne an interesting
> > > path to go.
> > >
> > > Thanks very much for doing these tests!
> > >
> > > Kees
> > >
> > >
> > > On 23 apr. 2013, at 04:29, Peter Friedrichsen <pfriedrichsen at sympatico.ca>
> > > wrote:
> > >
> > > > Kees,
> > > >
> > > > I went ahead to try to measure the amount of UV transmitted through some
> > > of these sensitizers+gelatin.
> > > >
> > > > I used a UV exposure unit that exposes gum dichromates in 4-6 minutes,
> > > and cyanotypes in about 10-12 minutes. I placed a UV sensor under a glass
> > > slide coated with these emulsions -pigment free.
> > > >
> > > > For roughly the same film thickness of gelatin+sensitizer, I found that
> > > DAS is a much stronger UV absorber at 6% of dried gelatin than potassium
> > > dichromate at 30% of dried gelatin. In fact, only about 14% of UV at 365 nm
> > > can get through the DAS+gelatin film vs PotDich+gelatin. Significantly more
> > > UV passed through Ferric ammonium citrate/Gelatin than either of these.
> > > Even after full exposure (curves were plotted), the UV transmitted through
> > > the DAS+gelatin was still much less at about about 16% of the
> > > PotDich+gelatin.
> > > >
> > > > I am thinking that this strong UV blocking ability of DAS would limit
> > > the depth to which the gelatin could harden to produce a relief. It would
> > > also suggest a more compressed scale.
> > > >
> > > > Peter Friedrichsen
> > >
> > > _______________________________________________
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> > >
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