[Alt-photo] Re: GUM: problematic yellow?

[Christina Anderson]

Luciano
I created this for my students which should take care of most scenarios.
On most processes for most papers I start with an overexposure time of 15 minutes, with cyanotype 30 minutes.
This usually produces max black on most papers. So, for 15 mn, it would go like this (please excuse if I've typed a mistake).
There are different OHP UV densities and maybe B+F film densities so those numbers would have to be plugged in but you get the idea.
You could probably fairly accurately use .9, .8 and .7 and those handy with calculators can do it MUCH easier, but the way this chart is laid out shows how it works.
To answer your question, you want to merge at least two steps but then move mathematically to only one step of max black.
Chris

CALCULATING PRINTING TIME
Base+fog of film step wedge = .89  1/3 stop = .794  1/2 stop = .707                 
Pictorico = 1/2 stop or .707 
(First remove B+F, then multiply by .794 for every third stop, then divide by .707 to add Pictorico B+F)
15 minute BPT:
1. (Step 1 is max black) 15 x .89 / .707 = 19 min
2. (Step 2 is max black) 15 x .89 x .794 / .707 = 15 min
3. (Step 3 is max black) 15 x .89 x .794 x .794 / .707 = 12 min
4. (Step 4 is max black) 15 x .89 x .794 x .794 x .794 / .707 =  9.5 min
5. (Step 5 is max black) 15 x .89 x .794 x .794 x .794 x .794 / .707 =  7.5 min
6. (Step 6 is max black) 15 x .89 x .794 x .794 x .794 x .794 x .794 / .707 = 6 min
7. (Step 7 is max black) 15 x .89 x .794 x .794 x .794 x .794 x .794 x .794  / .707 =  4.75 min
8. (Step 8 is max black) 15 x .89 x .794 x .794 x .794 x .794 x .794 x .794 x .794  / .707 =  3.75 min
9. (Step 9 is max black) 15 x .89 x .794 x .794 x .794 x .794 x .794 x .794 x .794 x .794  / .707 = 3 min
10. (Step 10 is max black) 15 x .89 x .794 x .794 x .794 x .794 x .794 x .794 x .794 x .794 x .794  / .707 = 2.5 min

Christina Z. Anderson
http://christinaZanderson.com/

On Feb 6, 2014, at 8:31 AM, Luciano Teghillo wrote:

> 
> Now I am a bit confused. I thought I was supposed to merge step 1 & 2, and
> then calculate the difference between the base of the Stouffer step wedge
> with the Pictorico base (multiply the time found by 0.9 and divide the
> result by 0.7). So I should choose the time from the last strip printed
> where step 1 and 2 do NOT merge? and then use this time to calculate the
> difference between the two bases?
> 
> Houston I think I have a problem here :-)
> 
> Luciano
> 
> 
> -----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
> Alberto Novo
> Sent: Thursday, February 06, 2014 2:15 PM
> To: alt-photo-process-list at lists.altphotolist.org
> Subject: [Alt-photo] Re: GUM: problematic yellow?
> 
> Yes for the minimum exposure time (the value which gives you the maximun
> "black" without merging steps 1&2). But if you will find that the amount of
> color is too much or too less, and you will be forced to modify the % of
> pigment in the mix, you have to find the new minimum exposure time because
> the pigment itself acts as a self-mask to UV. This depends on the pigment
> and cannot be generalized (UV absorption is independent on visual density). 
> 
> Alberto 
> 
>> 
>> I think that when I start layering the colors I will have to make 
>> other adjustments, either to the exposure time, color mix, or 
>> negative. But for now I was wondering if for blue I should use an 
>> exposure of 2 minutes (as indicated by looking at the color page) or 3 
>> minutes (as indicated by looking at the grayscale version). In 
>> summary, are you suggesting that is best, as a starting point, to 
>> evaluate the exposure time by looking only at the grayscale version?
>> 
>> Luciano
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