Fine tuning simple cyanotype to your negatives

[zuluz]

One of the main advantages of Mike Ware's 2019 Simple Cyanotype, at least for me, is that you can tailor the chemistry to your negatives, i.e., the negatives your printer/ink system is capable of producing. Mike Ware gives the recipes for three versions, the only difference being the amount of ammonia solution in them:

1. Low Contrast: Exposure Scale ~2.7
2. Medium Contrast: Exposure Scale ~2.3
3. High Contrast: Exposure Scale ~1.8

But what's more interesting is this:

"Intermediate degrees of contrast with Exposure Scales lying between 2.7 and 1.8 can be obtained by mixing sensitizer solutions 1 and 3 proportionally."

If one could print the perfect negatives, then there would be no question that using the low contrast solution would give the widest scale. But I use a Canon PRO-100 with a limited capacity to block UV, and, therefore, far from perfect negatives. Here's what I had to do to get the most optimal chemistry for my setup:

First, I made the three solutions, named as:

• CSL: the low contrast solution
• CSH: the high contrast solution
• CSM: the medium contrast solution, which is equivalent to a 1:1 mix of CSL+CSH

Then did the following exposure test: exposing a black strip at 2m intervals, for each solution.

As you see, each has a different optimal Dmin-Dmax range. Here's what the density graph looks like in terms of grayscale K% at different exposure times:

The hockey-stick style lines going to the top are the Dmax's. For my setup (chemistry and paper) the highest Dmax I can get is capped at K=75%. But each version rises up to that level at different speeds.

The lower three lines are the Dmin's. You can see how CSL's Dmin rises much more rapidly than the other two, making CSL the worst option for my setup. Here's a better view of the tonal range (Dmax-Dmin) for each solution:

For my setup the best I can do with each solution is:

• CSL @4min: Dmax=69% Drange=64
• CSM @10m: Dmax=74% Drange=73
• CSH @12m: Dmax=73% Drange=71

So out of the three, CSM is the best chemistry for me. It's not giving me the highest Dmax possible, but it's good enough, and instead is giving me the widest tonal range. Had the 50% CSM turned out not to be good enough, I could have experimented with other ratios of CSL+CSH to find the optimal chemistry. In my case, I can push it up to a 58% solution, but then it's downhill from there.

Hope this is useful.

 

[BrianShaw]

Very interesting information. Thanks! I’ve not yet used Ware’s formula and now looking forward to trying it.

 

[koraks]

CSM @10m: Dmax=74% Drange=73

The plots do suggest that you'll need a strongly non-linear compensation curve to get a linear printed (in cyanotype) output. This matches with my experiments some years ago trying to make digital negatives for cyanotype which, as I recall, also had distinct hockey-stick curves to them. I'm curious what you're going to run into when trying to linearize things. My guess is that you may find out that a different optimum at a shorter exposure time (ca. 4.5 minutes) may give better tonality, but at the cost of some lower dmax.

 

[nmp]

Nice study. I love stuff like this. This is very similar to what you can get with the classic chemistry but by modulating the pH of the development bath. With neutral(ish) plain water, you get higher contrast. With acidic bath, the contrast goes down - Dmax goes up, Dmin goes up. Using citric acid, I found that this effect leveled off at about 0.25% w/v, above which there was no change. Analogously, in the case of Simple chemistry as demonstrated above, the lower contrast formula uses less ammonia, i.e. it is more acidic than the higher contrast formula. Acidic environment allows greater conversion to Prussian blue from ferrous ammonium citrate and ferricyanide.

Couple of additional observations:

1. It seems that the higher contrast formula adds a lot of coarseness to the image, which also extends to the middle grade as well. I don't know if this is real (i.e. repeatable) or not. If it is, you might have to add a surfactant or do something with the paper to counter it, to the extent that it transfers to an actual image.

2. It is interesting that even as Dmax curve for CSM is nearly the average of CSL and CSH, Dmin curve moves all the way down close to that of CSH. It is possible that you may not need a lot of CSH in the mixture to bring down the Dmin while still enjoying the higher ultimate Dmax of CSL. Based on this rationale, perhaps it is better to go less than 50% CSH rather than higher to get longer DR.

:Niranjan.

 

[zuluz]

Couple of additional observations:

1. It seems that the higher contrast formula adds a lot of coarseness to the image, which also extends to the middle grade as well. I don't know if this is real (i.e. repeatable) or not. If it is, you might have to add a surfactant or do something with the paper to counter it, to the extent that it transfers to an actual image.

2. It is interesting that even as Dmax curve for CSM is nearly the average of CSL and CSH, Dmin curve moves all the way down close to that of CSH. It is possible that you may not need a lot of CSH in the mixture to bring down the Dmin while still enjoying the higher ultimate Dmax of CSL. Based on this rationale, perhaps it is better to go less than 50% CSH rather than higher to get longer DR.

That's right. For better tonality, less graininess, I have to go to about 58-60% CSL in the mix at the expense of Dmax and Drange. It's a little disappointing, since now there's a third parameter to optimize in all of this; Dmax, Drange, and now Tonality.