Classic vs. Simple Cyanotype Exposure Time

zuluz · Mar 24, 2023

I recently decided to try simple cyanotype based on the desire to get a better tonal range. Got all the stuff from B&S, then prepared the low contrast (~2.7 scale) sensitizer according to the instructions. For the classic, I'm using the Formulary A+B solutions mixed 1:1. Both developed in 1% citric acid first, then washed in water pH ~6.5.

The following is the result of a side-by-side exposure of two 21-step wedges for both Simple and Classic. Both on COT 320 paper and exposure was 64 minutes, simultaneously. As you see, the range is much better in Simple, which is great. However, I expected to get the same or faster exposure time for Simple. But as you can see, the Dmax exposure time for Simple is almost 3x of the Classic, ~57m vs ~20m.

I'm guessing it must be my Simple sensitizer that is out of wack. Any ideas what may be going on, given that everything is the same in this comparison except the chemistry?

nmp · Mar 24, 2023

I made the simple sensitizer, but never used it so I can't comment from personal experience on how the speed compares with the classic version. This reference claims that the exposure times should be comparable, but who knows - sometimes you get what you get:

https://www.specialeditionartprojec...t/making-of-the-arts/world-cyanotype-day.html

I am also noticing that the Simple one has a lot more fog/stain too (but with a greater Dmax.) If your negative can take it, I would consider making the "normal" DR sensitizer or perhaps try a less acidic developer.

:Niranjan.

zuluz · Mar 24, 2023

Thanks @nmp, I will try a less acidic developer for the staining.

I’m also wondering whether the optimal UV wavelength for Simple might be different than Classic? My UV box uses fluorescent tubes and not sure what the exact wavelength is. Maybe it’s time to build an LED panel.

nmp · Mar 25, 2023

zuluz said:
I’m also wondering whether the optimal UV wavelength for Simple might be different than Classic? My UV box uses fluorescent tubes and not sure what the exact wavelength is. Maybe it’s time to build an LED panel.

I would be surprised if that were true - considering in the end they both use the ferric ammonium citrate molecule as the photoactive compound. Tubes give out a kind of broad band of radiation, centering around 360'sh nm. For LED, the radiation is pretty much single wavelength at which it is rated. The cheaper ones are ~395 nm, while shorter ~360 nm LED's are more expensive. I think different processes prefer one or the other. You can do some research here on Photrio where many who have moved from tubes to LED have reported significant gain in speed - my own experience has been somewhat muted when I tried out 395-400 nm LED's over my old box made of BLB spirals. May be it's the processes I am using or may be I packed the old one with too many bulbs together (18 of them, with 12 watts each, in a 12x16 box.)

Welcome to Photrio, by the way.

:Niranjan.

zuluz · Mar 25, 2023

Thanks, Niranjan! I started gutting my uv box. Waiting for the power supply and the VerifiedUV strip to arrive. Will report back once I redo the test.

FotoD · Mar 25, 2023

Speed will be faster at 365nm than around 400nm with cyanotypes. IME fluorescent tubes with a peak at 365nm work really well with ferric ammonium citrate and oxalate.

fgorga · Mar 25, 2023

FotoD said:
Speed will be faster at 365nm than around 400nm with cyanotypes. IME fluorescent tubes with a peak at 365nm work really well with ferric ammonium citrate and oxalate.

View attachment 333582

Your statement regarding speed is only true if the intensity of light is the same for both light sources (i.e. tubes vs. LEDs). This may or may not be true for any given source.

Additionally, can you provide a reference for the graph you show. I am interested in the details.

Thanks.

FotoD · Mar 25, 2023

I'd be happy to.

From ultraviolet to Prussian blue: a spectral response for the cyanotype process and a safe educational activity to explain UV exposure for all ages - PubMed

Engaging students and the public in understanding UV radiation and its effects is achievable using the real time experiment that incorporates blueprint paper, an "educational toy" that is a safe and easy demonstration of the cyanotype chemical process. The cyanotype process works through the...

pubmed.ncbi.nlm.nih.gov

koraks · Mar 25, 2023

fgorga said:
Your statement regarding speed is only true if the intensity of light is the same for both light sources

Indeed, and that seems to be a very significant caveat. My experience so far is that per Watt of RMS power provided to the light source, 400nm LEDs give the most density in the processes I tried, followed by 365nm LEDs and then tubes. The difference in efficiency of the light sources themselves appears to be great enough to totally overwhelm the effects outlined in the chart above, at laest in my experience so far.

Simply put: even if theory suggests that a 365nm light source will be faster, 400nm LEDs are hard to beat, simply because they're more efficient. Coincidentally, they're also cheap on a per-Watt basis. Double gains.

fgorga · Mar 26, 2023

FotoD said:
I'd be happy to.

From ultraviolet to Prussian blue: a spectral response for the cyanotype process and a safe educational activity to explain UV exposure for all ages - PubMed

Engaging students and the public in understanding UV radiation and its effects is achievable using the real time experiment that incorporates blueprint paper, an "educational toy" that is a safe and easy demonstration of the cyanotype chemical process. The cyanotype process works through the...

pubmed.ncbi.nlm.nih.gov

Thanks! Interesting read.

zuluz · Mar 31, 2023

Here's the latest side-by-side test with my new UV box. I replaced the 4x15w BLBs with strips of VerifiedUV (v2) LEDs (60w total) 14mm apart. The LEDs are rated at 365nm. I'm seeing a much faster exposure for Simple and the same for both Simple and Classic at about 14m. The only conclusion I can make is that the BLBs I had were much slower for Simple but ok for Classic.

nmp · Mar 31, 2023

That was quick. Thanks for the update. Always nice to see head-to-head comparison.

Interesting that the benefit of VerifiedLED was much less pronounced in the case of Classic than in Simple (less than 1 stop vs almost 2 stops resp.) Dmax relationship between the two stays.

Keep sharing!

:Niranjan.

FotoD · Apr 3, 2023

Thanks for the follow-up!

Do you think you could mix the two sensitisers for contrast control? Like 10 drops simple and 10 drops classic for medium contrast?

zuluz · Apr 3, 2023

FotoD said:
Thanks for the follow-up!

Do you think you could mix the two sensitisers for contrast control? Like 10 drops simple and 10 drops classic for medium contrast?

Simple already has instructions for controlling contrast (low, medium, high): https://www.mikeware.co.uk/downloads/SimpleCyan.pdf
I have only prepared the low contrast so far. I'll do some experiments as you suggested later on. Thanks.

PGum · May 11, 2023

zuluz said:
Here's the latest side-by-side test with my new UV box. I replaced the 4x15w BLBs with strips of VerifiedUV (v2) LEDs (60w total) 14mm apart. The LEDs are rated at 365nm. I'm seeing a much faster exposure for Simple and the same for both Simple and Classic at about 14m. The only conclusion I can make is that the BLBs I had were much slower for Simple but ok for Classic.

View attachment 334332

Hi Zuluz,

Its interesting that the number of steps in the classic is greater with your old lamps. I found the same thing. With 385 leds, less steps and more contrast. With my old 365 cfl fluorescent spirals, less contrast longer scale. I am wondering if it is exposure length not wavelength that gives a longer scale with classic. My led unit exposes in 8 mins, while my old one took about 25. I always liked the scale with the old one better, and also less grainy which is probably due to the reduced contrast. It remains a mystery however. For the simple cyanotype, doesn’t seem to be an issue.

Classic vs. Simple Cyanotype Exposure Time

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