Re: cyanotype question

Mark,

Yes. You have it right as far as the mergers are concerned but I don't follow you on the question about 2 additional steps merging at 750 units. No steps merge at 250. Three steps merge at 500 which indicates the low end was pushed up the scale 2 steps as an additional 250 units was given. The same thing happened as the exposure was further increased by 250 units to 750, i.e., the low end was pushed up the scale another 2 steps. This is also showing in how many steps solarized initially. The highest solarized steps were 6, 8, and 10 for the 250, 500, and 750 unit exposures, respectively. The low steps are acting in a consistent manner gaining 2 steps with each additional 250 unit exposure. It is the high end that is behaving strangely showing a decrease in the rate that the tones print as exposure is increased.

I did time one 250 unit exposure cycle and the duration was 13 minutes. I don't see how changing the drying procedure would affect the outcome because the entire sheet was coated and dried before being cut into strips and exposed.

So, if I'm reading your reply correctly you are perhaps suggesting that the exposure scale increases as the print sits around waiting to be processed? Since the 250 unit exposure produced the longest scale and was completed approximately one-half hour before the 750 unit exposure was completed (at which point all test strips were processed together), then simply leaving an exposed but unprocessed print laying around would increase the scale perhaps??? Approximately one full stop (1.63-1.31=0.32) was gained. If this is actually happening due to some temporal effect between exposure and processing then simply processing two similarly exposed strips (say 250 units each) with some delay between them (e.g., 30 minutes), should produce different tonal scales. That would be easy enough to check by identically exposing one strip and then the other sequentially rather than giving an identical simultaneous exposure to both.

Maybe what is happening is that the UV exposure produced by the NuArc is decreasing as the bulb heats up and stays on for an extended time after the brief restarts when I pulled one strip from the unit. I had assumed the integrator controlled the output though so that sort of variation wouldn't occur.

Has anyone else found the UV output to decrease from one of these units with an integrator as exposures are lengthened? Maybe I've just got a bad integrator. Does anyone know if the integrators need to be periodically calibrated/adjusted in some way?

Joe

>>> Ender100@aol.com 09/02/04 9:49 PM >>>
Joe,

If I am understanding correctly:
250 Units - no merged steps
500 units - Steps 1, 2 & 3 are merged
750 units - Steps 1―5 are merged

That's an interested effect―you would expect the exposure scales to be
approximately the same and they are getting shorter with longer exposures. It's also
odd that with 750 Units you got two additional steps merging, where there
should have just been one.

You might try reversing the exposure process and see if the same thing holds
true―put one strip in for 250 units, add another one for another 250 and then
add the 3rd for the final 250―see if you get the same effect in reverse order.

There may be some issue with the amount of time between exposure and
development.

There may be some other factor intervening, such as humidity, etc.

What if you let the emulsion air dry before exposing instead of using the
hair dryer?

What do you figure is the appropriate exposure time?

Mark Nelson
www.precisiondigitalnegatives.com
www.markinelsonphoto.com

In a message dated 9/2/04 6:33:03 PM, jsmigiel@kvcc.edu writes:

> Mark, et.al.,
>
> Yes. using a 21-step wedge.* Here's the cyanotype test data in a different
> form:
>
> An exposure of 250 units resulted in distinct printed tones from step 1 to
> 12 with step 13 remaining the tone of the paper after processing.* The
> original exposure solarized to step 6 before processing.* The transmission density
> of the steps of the stepwedge were 0.03 for step 1 and 1.66 for step 12.* Step
> 13 has a transmission density of 1.80.* So the range of densities that
> actually printed was 1.63 (1.66-0.03).
>
> 500 units printed steps 3 to13 (w/step 14 at no tone) with density values of
> 0.35 and 1.80 respectively giving a range of 1.45 which was less than the
> shorter exposure.* This exposure solarized to step 8 before processing.
>
> 750 units produced steps 5 to 14 (w/step 15 no tone).* Density values were
> 0.64 and 1.95 for a range of 1.31, again lowering as increased exposure was
> given.* The 750 unit exposure solarized through step10 before processing.
>
> So, it appears an exposure of 250 units was optimum for this paper and
> emulsion batch.* Less exposure did not achieve the same maximum dark print tone.*
> (150 units printed tones from step 1 to 11 with a weaker step 1.)* The
> exposure range is decreasing as exposure is increasing going from 1.63 @ 250 units
> to 1.45 @ 500 units and 1.31 @ 750 units.
>
> This also brings up an additional question.* If I read a standard reference,
> certain negative density ranges are always suggested for specific
> processes.* For example, Schaefer suggests "1.60 or higher" as being correct for
> cyanotype and "a density range in excess of 1.85" as being correct for POP.* James
> says 1.4 to 1.6 for cyanotype and 1.8 to 2.0 "works well" for POP.
>
> So there is some variation in reporting optimum negative density ranges.*
> But, to what do these values refer?* I've always assumed the range given was
> from textured highlight to textured shadow in a negative but this does not
> translate directly to the stepwedge.* That certainly isn't the same as from
> minimum to maximum step printed or from max d to clear in the print.
>
> Given that the total range I got from the cyanotype emulsion was 1.63 (w/250
> units exposure) from darkest to lightest printed density (excluding the
> clear paper base tone) suggests that James' values probably work better for me
> since he bases his ranges on textured negative values and not just tones
> without detail.* However, Crawford talks of optimum negative densities for
> cyanotype being about 1.60 and "negatives with a density range of 1.70 in order to
> print the full scale of tones from'paper white' to 'maximum black'" for POP.*
> This again corresponds nicely to my present test but leads me to believe some
> authors relate the density ranges directly to step wedges without regard for
> negative detail or texture, just tone.
>
> Is there a standard way of reporting the densities?
>
> This is making my brain hurt.
>
>
Received on Thu Sep 2 21:12:35 2004