[alt-photo] Re: back again

[Christina Anderson]

Ya, agree Loris. When I first started casein I thought the exposures were similar to gum, one colloid to another. Not at all. 2 stops faster.

It is hard to communicate by email, but IF there is "no image" meaning you have got a coating of pigment/casein hardened on the paper and no image appears in it, that is overexposure and wrong curve. If the whole coating of pigment/casein washes off so it is paper white, that is underexposure. That happens readily with cyanotype. I never had casein EVER slough off. But that also could have to do with my pigment choices maybe hardening the casein or some other. UVBL unit.

I even considered going down to 30 seconds exposure. 

I promise I'll get more scientific about this when I finish writing and go back in the dimroom but right now it isn't going to happen, so this is all from memory and others should chime in.
Chris

Christina Z. Anderson
christinaZanderson.com

On Oct 24, 2011, at 7:54 AM, Loris Medici wrote:

> Matti,
> 
> With my old lightsource cyanotype exposures with (thin) paper negs were
> around 60 mins. too. Therefore, I assume our conditions (combination of
> lightsource, paper, emulsion...) are similar. With the same lightsource,
> using paper negs and 10-15% (amm.) dichromate, my gum exposures were around
> 6 mins. (average), I never tried casein with paper negs but IME, at the same
> conditions, casein was at least 1 - 1.5 stops faster than gum. So, I'm with
> Christina here; 40 minutes sounds a little too much. ???
> 
> As a note: My casein layers were considerably thinner than my gum layers
> FWIW...
> 
> 
> -----Original Message-----
> From: alt-photo-process-list-bounces at lists.altphotolist.org
> [mailto:alt-photo-process-list-bounces at lists.altphotolist.org] On Behalf Of
> Matti Koskinen
> Sent: 24 Ekim 2011 Pazartesi 14:08
> To: The alternative photographic processes mailing list
> Subject: [alt-photo] Re: back again
> 
> Hi,
> Yes
> 40 min. Same uv-light cyanos are one hour. But coating succeed with heavier
> layer, then brushing and rolling as in tempera. Because heavier layer, even
> 40 min was not enough. Had to use sodium carbonate to get anything visible,
> but that lost details too.
> -matti 
> 
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