[alt-photo] Re: back again

[Joseph Smigiel]

I might suspect the glass is absorbing UV.  My casein exposures were  
always briefer than gum and on the order of one minute or less IIRC.   
I never pursued casein because I felt gum was more controllable with  
the longer exposures (1-6 minutes).

joe


On Oct 24, 2011, at 10:04 AM, Christina Anderson wrote:

> 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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