[Alt-photo] suggestions about cyanotype curve

Bob Cornelis bob at colorfolio.com
Tue May 23 15:30:45 UTC 2017


Thank you Alberto, Keith and Dan for the responses! I see a consensus here. I have a couple of questions to further my conceptual understanding of why you’re making this suggestion, which I will definitely test out - forgive me if these are beginner questions, this is the first time I’m wrestling with some of these parameters. I’m also attaching my screenshots again because at least one person has said they were missing from my last email.

It might help to note that these are printed with a colorized neg - using the testing suggested in Mrhar’s book, I determine that a particular shade of orange gave the best UV blocking. Dmax was determined using a standard test of different exposure times to determine at what point the dmax under the Pictorico Ultra film matched that of the uncovered, sensitize paper. 

The file PreCurve shows a 100 step wedge printed with those parameters and no adjustment curve. Basically the range of tones is limited to about patch 70 on the dark end and 11 on the light end. Everything higher than 70 is the same max black and everything under 11 is pure white. Patches 11-70 contain all the distinct values of the compressed tonal range of the Ware cyanotype on this paper. The PostCurve file shows the same chart after adding my adjust curve create from PreCurve. You can see that steps 0-5 are white and then there is a big jump at step 6 and after that, the tonal range isn’t bad the rest of the way. 

Your suggestion is to lower ink density in the neg, which would lead to a darker print with the same exposure time. I can do this in the color density slider in the epson driver or I could use a longer exposure time, if I’m not mistaken. Are these equivalent, except for the fact that the former would result in using a slight amount less ink and be a faster exposure?

I think what the result of doing this would be that the range of distinct tonal values in the Precurve target which are currently 11-70 would shift downward though still consist of the same number of patches. For example, instead of 11-70, the range might be 5-64. There will be more pure black patches and fewer pure white patches. I think that this would lead to more “work” being needed in the last 10% of the curve representing the darkest values and less work being needed in the (currently problematic) last 10% of the highlight part of the curve. Currently this is the case and the PostCurve I end up with does much better with the darker values, so maybe a further shift in this direction is a good thing. Is that the goal? Why would the PS curve handle adjusting a wider range of pure black values to their proper tones rather than the tones in the top highlight range? Maybe it’s easier to lighten tones that are already there than to introduce tones into pure white?

Is my characterization of what would happen to my PreCurve correct? Why would this help the end result? Certainly I will test this and find out what happens and if it helps, but I’m interested in why this would be the case or if I’ve got it wrong to begin with.

This conversation is extremely helpful to me on both a practical and conceptual level, so thank you again for chiming in!

Regards
Bob




--------------------------------------
www.bobcornelis.com





On May 22, 2017, at 11:37 PM, Alberto Novo via Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org> wrote:

> I agree with Keith who is agreeing with Don.
> You could print a few test prints with -5%, -10% and -15% ink and find which is the best. If you are used with maths, you could also plot the density values to find the right amount of ink.
> 
> Alberto 
> 
>> I agree with Don. You need to dial down the Dmax on your neg a bit. I'm not sure how to do that with the method you are using to make them. If it uses the Epson driver, maybe you can go into Advanced Media Control and change the Color Density setting to -10% and see if that is enough. Of course, you will have to make a new correction curve afterwards since it will decrease density throughout the scale.
>> 
>> Cheers,
>> Keith
>> 
>> Keith Schreiber
>> jkschreiber.com
>> 
>> 
>> 
>> 
>>> On May 22, 2017, at 12:49 PM, Don via Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org> wrote:
>>> 
>>> Sounds like you have too much UV blocking with your digital negative. 
>>> 
>>> Have you printed a regular analog step tablet to determine the contrast
>>> range of your process?
>>> 
>>> Just a thought.
>>> 
>>> Don Bryant
>>> 
>>> -----Original Message-----
>>> From: Alt-photo-process-list
>>> [mailto:alt-photo-process-list-bounces at lists.altphotolist.org] On Behalf Of
>>> Bob Cornelis via Alt-photo-process-list
>>> Sent: Monday, May 22, 2017 1:25 PM
>>> To: alt-photo-process-list at lists.altphotolist.org
>>> Cc: Bob Cornelis
>>> Subject: Re: [Alt-photo] suggestions about cyanotype curve
>>> 
>>> Hi Peter
>>> 
>>> Thanks for the suggestion. I think, however, that my problem is not lack of
>>> contrast but, rather, too much contrast, at least in the highlights. The
>>> rest of the tonal range, all the way down to the shadows are behaving
>>> properly.
>>> 
>>> Regards
>>> Bob
>>> 
>>> 
>>> On Mon, May 22, 2017 at 10:10 AM, Peter Friedrichsen via
>>> Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org>
>>> wrote:
>>> 
>>>> Bob,
>>>> Without seeing your samples, I can suggest one possibility; a thick
>>>> coating of the sensitizer. I have found that contrast increases, the more
>>>> one applies to the paper. It may be due to the uv blocking effect such
>>> that
>>>> the sensitizer that is bound to the paper never gets a chance of exposure
>>>> in the shadow areas due to the filtering effect of the sensitizer sitting
>>>> overtop. Whatever the reason, that is my observation. I know others will
>>>> suggest other possible causes.
>>>> 
>>>> Peter Friedrichsen
>>>> 
>>>>> On May 22, 2017, at 11:04 AM, Bob Cornelis via Alt-photo-process-list <
>>>> alt-photo-process-list at lists.altphotolist.org> wrote:
>>>>> 
>>>>> Hi All
>>>>> 
>>>>> I'm looking for a little help finishing a custom curve I've made for
>>> Ware
>>>>> cyanotype printing using Peter Mrhar's method from Easy Digital
>>>> Negatives.
>>>>> 
>>>>> I'm having problems getting a smooth gradient from steps 0-10. Pure
>>> white
>>>>> is step 0, pure black step 100. My tones from steps 10-100 are pretty
>>>>> linear, but within the highlights I've got about half the steps pure
>>>> white
>>>>> and then there is a steep jump to a value of close to 10. I'd like to
>>>> find
>>>>> a way to get a smooth gradient in this part of the tonal range.
>>>>> 
>>>>> Without a curve, all steps from 0-14 are pure white so the curve has to
>>>> do
>>>>> a lot of work to introduce a gradient in a relatively small portion of
>>>> the
>>>>> curve range. I've tried tweaking with the curve in that range by hand
>>> but
>>>>> without success.
>>>>> 
>>>>> I was wondering if there are other tricks people know of to handle this
>>>>> type of situation, either chemically, through exposure, development,
>>> etc.
>>>>> 
>>>>> My first wash is in 3% citric acid for a couple of minutes, 20 sec in
>>>>> peroxide solution, then about 25 min in water.
>>>>> 
>>>>> I've attached 3 screenshots for anyone interested showing my pre-curve
>>>> and
>>>>> post-curve step wedges (100 steps), and the curve itself (note it is a
>>>>> pre-inversion curve).
>>>>> 
>>>>> Thanks!
>>>>> Bob
>>>>> 
>>>>> 
>>>>> --
>>>>> 
>>>>> http://www.bobcornelis.com
>>>>> _______________________________________________
>>>>> Alt-photo-process-list | altphotolist.org
>>>> _______________________________________________
>>>> Alt-photo-process-list | altphotolist.org
>>>> 
>>> 
>>> 
>>> 
>>> -- 
>>> 
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>>> www.colorfolio.com
>>> 
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