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

[Christina Anderson]

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

On Feb 6, 2014, at 10:54 AM, Luciano Teghillo wrote:

> 
> Christina,
> 
> In my case then, and if I understand correctly, when step 1 & 2 merge with
> an exposure time of 2 minutes, I should:
> 2 x .89 (base+fog of film step wedge) x .707 (1/2 stop because I use a 21
> steps step wedge) / .707 (Pictorico base)
> 
> In reality I should only multiply by .89 to remove base+fog of the step
> wedge since multiplying and dividing by the same number (.707) yields the
> same result.
> 
> So my printing time is 1.78 minutes which is probably still best rounded at
> 2 minutes, correct?
> 
> 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
> Christina Anderson
> Sent: Thursday, February 06, 2014 5:49 PM
> To: alt-photo-process-list at lists.altphotolist.org
> Subject: [Alt-photo] Re: GUM: problematic yellow?
> 
> 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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