Re: cyanotype question

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 19:50:17 2004