Re: cyanotype question

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.

Joe
>>> Ender100@aol.com 09/01/04 6:35 PM >>>
Joe,

It would be easier for me to understand if you also told how many steps
showed tone and how many steps were merged. Also, it would be easier if you had
done 250, 500, 1000 units―or doubled the exposure each time. I am assuming you
are using a 21 step tablet?

Mark Nelson
www.precisiondigitalnegatives.com has been updated!
www.markinelsonphoto.com

In a message dated 9/1/04 4:55:54 PM, jsmigiel@kvcc.edu writes:

> When the strips dried, the exposure scales appear to be different, not
> just shifted between steps as exposure increased.* (The strips did show
> a shift in position towards higher steps as exposure increased.) The 250
> strip had tones covering 1.63 density units, the 500 was 1.45, and the
> 750 was 1.31.* The density figures are transmission densities of the
> step wedges as measured on an X-rite 301 densitometer and the printed
> densities were judged visually.
>
Received on Thu Sep 2 17:27:11 2004