Developing a negative for cyanotype

[Phillip P. Dimor]

I'm going to be printing solely cyanotypes as I only have 4x5 negs and the sun to work with. I understand/believe that cyanotypes need a denser negative.
I am seriously rusty/brain-dead, how do I go about this? Less development time? A lower EI? I've no access to a densitometer out here but my negatives are traditionally a little on the thin side. Any tips/textbook answers would be awesome! I've looked around and can only find that I need a density of 1.4 to 1.6 (i think?) but that doesn't help me so much..

 

[Jeremy]

You need more development time so that you are building up more and more density. To compensate for the longer development time you need to shoot at a faster film speed so that the shadows are still at the right point when the highlights reach their proper "thickness."

 

[psvensson]

Try developing maybe 20 percent longer than manufacturer's recommendations for diffusion enlargers, which generally call for a density range of 1.2-1.25. You can probably use the film's box speed.

If your negs still turn out too flat, I believe you can add a bit of dichromate to the cyanotype sensitizer to bump up its contrast.

 

[Digidurst]

This is a confusing issue for me as well. I don't do cyanotypes (yet) but argyrotypes but since I don't have a densitometer, I've just been using "the force". I wonder if it would be possible for someone to scan a 'high density' negative as well as a 'regular' negative so that we can get a visual for what to look for?

 

[psvensson]

If you have a light table and a light meter with a small sensor (ideally, a spot meter), you don't need a densitometer. Meter through the thinnest part of the neg that you want to show faint detail (Zone I) and record the value. Then meter through the densest part of the neg that you want to show detail (Zone VIII). Subtract the higher reading from the lower and multiply the number of stops by 0.3 to get the density range. A stop of light is the equivalent of a 0.3 density change.

For cyanotypes, the difference between the two readings should be 1.4/0.3 = 4 2/3 stops.

 

[Donald Qualls]

More development with give a negative with more contrast. More exposure will give more overall density.

However, my limited experience with (traditional) cyanotype is that it has much less self-masking effect than other UV-sensitive processes, because the reacted Prussian blue in the image doesn't block UV as strongly as printed out silver in POP, salted paper, etc. My best cyanos have been from negatives that were only barely on the contrasty side (close to what I'd consider normal for LF, as opposed to normal for roll film or 35 mm), not the heightened contrast I'd expect to need for, say, platinum. And you can always add a drop or two of 2% potassium dichromate to the sensitizer for a 5x7 if you find you're getting flat prints; it's hard to impossible to reduce the contrast if there's too much in the negative.

 

[Ole]

"Normal" LF negatives should be fine as Donald says. In the not so very rare cases where the negative is too contrasty, it seems that a pinch of oxalic acid in the sensitizer might be of help. At least I got good results with my first mix which contained a pinch of oxalic acid, while what I've made lately seems too harsh. Time to open the "poisons" cupboard again...

 

[psvensson]

However, my limited experience with (traditional) cyanotype is that it has much less self-masking effect than other UV-sensitive processes, because the reacted Prussian blue in the image doesn't block UV as strongly as printed out silver in POP, salted paper, etc.

You're right - there isn't much self-masking going on. According to Mike Ware's book on cyanotype, this is because much of the exposed salt turns into Prussian White, which doesn't absorb UV. It later turns into Prussian Blue by aerial oxidation.