ISO of cyanotype paper?

[Aidan G]

Hello I am wondering how sensitive cyanotype paper is. I have been doing some experiments lately with cyanotype paper and I am just curious if it has a set ISO or if it can be determined.

 

[removed account4]

Hi Aiden G
Are you asking about pre-made cyanotype paper or paper you coat your self using one of the various formulae?
Some formulas are more sensitive to UV light than others ... so to answer your question "it depends"... and it might be kinda-sorta-slow..
Have fun !
John

 

[Aidan G]

I am using pre made Sun Print paper. The packaging says that it should be exposed to the sun for 1-5 mins. I have done some experiments with in camera cyanotypes some interesting results. The exposures range from 2-9 hours and give somewhat visible images. I am just wondering if there is a way to determine the ISO of it so I can time the exposures better. I'm assuming it would way be under 1 ISO due to it not being very sensitive and that it only reacts to UV light.

 

[Truzi]

I have no idea what the ISO is, but if it helps, I put a 4x5 negative on a piece of Sun Print paper in my office at work. Objects started to make shapes after an hour or so, but it took longer for a decent print from a negative.

After about 6 hours the fluorescent lights made a decent image. This is an office area with a lot of larger fluorescent lights, though. The exposure was about 5 feet below them, on a shelf. You can experiment with a CFL or something. You could cover part of the print with something to block the light, after an hour uncover more, after another hour uncover a bit more, etc.

This may not give you a "speed," but can give you some idea of how long you want your exposures.

 

[jim10219]

ISO doesn't really work with cyanotypes. The reason being that cyanotypes are mostly reactive to UV light, and light meters meter UV light differently (or not at all) than visible light. So even if you knew the ISO of a paper in question, any light meter you used would probably give you inaccurate readings.

That's not to say that a system couldn't be devised to figure out how to expose cyanotype negatives. But your best bet it to do some test runs, and see what timing works best and at what apertures. Keep in mind that if you're using natural light, UV light doesn't correspond directly to visible light. For instance, clouds effect visible light more than UV light. And the season (angle of the earth to the sun) effects UV light more than visible light. So a cloudy summer day at noon might give you more UV light and less visible light than a sunny winter day at noon, even though a traditional light meter will tell you the opposite. Elevation and latitude will also change your results. The higher up you go, the less atmosphere you have to filter out the UV light. The visible light will increase at elevation too, but not to the degree of UV light. Also, the further you get away from the Tropics of Capricorn and Cancer, the less UV light you'll have, especially in the winter months.

So if you're running your tests outside in the sun, your test numbers may only be good for about a month or so, and only during the same hours and weather conditions which you ran your tests. If you run enough tests on enough days and keep detailed notes of all of the factors involved, you'll start to figure out some patterns to make things more predictable. But for the most part, I'd either rely on test prints or bracketing if exposure is important.

 

[Luckless]

ISO doesn't really work with cyanotypes. The reason being that cyanotypes are mostly reactive to UV light, and light meters meter UV light differently (or not at all) than visible light. So even if you knew the ISO of a paper in question, any light meter you used would probably give you inaccurate readings.

That's not to say that a system couldn't be devised to figure out how to expose cyanotype negatives. But your best bet it to do some test runs, and see what timing works best and at what apertures. Keep in mind that if you're using natural light, UV light doesn't correspond directly to visible light. For instance, clouds effect visible light more than UV light. And the season (angle of the earth to the sun) effects UV light more than visible light. So a cloudy summer day at noon might give you more UV light and less visible light than a sunny winter day at noon, even though a traditional light meter will tell you the opposite. Elevation and latitude will also change your results. The higher up you go, the less atmosphere you have to filter out the UV light. The visible light will increase at elevation too, but not to the degree of UV light. Also, the further you get away from the Tropics of Capricorn and Cancer, the less UV light you'll have, especially in the winter months.

So if you're running your tests outside in the sun, your test numbers may only be good for about a month or so, and only during the same hours and weather conditions which you ran your tests. If you run enough tests on enough days and keep detailed notes of all of the factors involved, you'll start to figure out some patterns to make things more predictable. But for the most part, I'd either rely on test prints or bracketing if exposure is important.

Only other "UV Gotcha", besides risk of sunburn, not covered would be for lenses.

Not all lenses transmit UV evenly when compared to other lenses. So if you establish an accurate "ISO equivalent" for your paper with one lens and metering method, this will probably not hold accurately if you switch to a different lens. And with some combinations of glass and coatings you may find your lens is effectively opaque to UV. Not really an issue if you're working with pinhole cameras, but important to keep in mind if you're trying to use a UV sensitive material with a large/complex lens.

And a really really "fun" gotcha, with some extra FU in there: Some lenses may act similar to polarized filters with UV - Transmitting notably different levels of light simply by twisting the lens 90 degrees. [Learned that while helping a friend track down wildly different lab readings on her project back in university.]

The really important takeaway for working with something you can't see: Keep good notes, pay attention to variables, and stay on top of procedural consistency.

 

[koraks]

ISO doesn't really work with cyanotypes.

This. It's a pretty hypothetical question which 'equivalent ISO' cyanotype has. If you'd want to express it in an ISO-style number, you'd be looking at a tiny fraction of 1. If you keep in mind that wet plate collodion hovers somewhere around ISO 1, and cyanotype is actually many stops below that, you end up with a figure like ISO 0.001. With of course all the caveats the others mentioned - only UV sensitive, with lenses blocking much of the UV if you're considering in-camera or enlarger exposures, etc.

 

[removed account4]

AidenG
sometimes manufactured sun print paper doesn't have the best coating on it, so it might be worth your while to buy yourself an inexpensive classic cyanotype kit ( 2 stock chemicals you put equal amounts of on the paper ) and you can coat your paper yourself and get consistent results. you can also buy powered FAC (green) and potassium ferricyanide ( or ferrocyanide they say will faster ) and mix your own and vary the amounts of chemistry you use to customize your formula to get the highest speed. I think I read that if you use one for the exposure and "develop" in the other chemical afterwards you can increase your speed ( if not mistaken, sometimes this is called CyanotypeREX when the chemistry is applied at different times ). There might be people over on alternativephotography.com who can give you samples and relativeISOs for mix your own, not sure about manufactured sun print though...

 

[auburnxc]

Aidan G, I have started working with in-camera cyanotype this year and I'm very excited about some of my preliminary results. In full, blasting sunshine I can get a decent exposure in about 17 and a half minutes. I'm using mass-produced Sun Art Paper right now, but also considering trying the low-cost cyanotype kits, to see if I can get a quicker exposure. My experiments with pinhole cameras have not gone well so far, but my Yashica-A has worked like a real champ. Like others have said, the ISO of this paper is likely going to be a very small fraction of 1.​

 

[Donald Qualls]

In full, blasting sunshine I can get a decent exposure in about 17 and a half minutes.

Neglecting reciprocity failure, and assuming wide open at f/3.5 (to minimize exposure time), this works out to an equivalent ISO speed of about 1/5000 or ~ 0.0002 (for this lens's combination of glasses, anyway).

 

[auburnxc]

Neglecting reciprocity failure, and assuming wide open at f/3.5 (to minimize exposure time), this works out to an equivalent ISO speed of about 1/5000 or ~ 0.0002 (for this lens's combination of glasses, anyway).

I knew someone out there would be able to figure this out! Thanks for the quick work. Awesome.

 

[Donald Qualls]

I knew someone out there would be able to figure this out!

Sunny 16 and a little quick arithmetic is all it takes.

 

[auburnxc]

I certainly appreciate the help. Math is not my strong suite and I had trouble getting the online exposure calculators to do what I wanted them to.

 

[koraks]

I'm using mass-produced Sun Art Paper right now, but also considering trying the low-cost cyanotype kits, to see if I can get a quicker exposure.

New Cyanotype is faster than classic, and it will also capture a higher dynamic range. For in-camera experiments, it should be superior. I'm sure you can get New Cyanotype kits as well as the classic type. I only mixed my own so never looked into ready-made kits or papers.

 

[auburnxc]

I think I will have to look into New Cyanotype. I really wanted to keep everything as simple as possible, but my pinhole cameras are all at least 4" deep, which I think means I'm shooting at f/280 or so.

 

[koraks]

You're going to be the expert in this, but I hold very little hope for in-camera pinhole cyanotypes. The concept is interesting, of course.
New Cyanotype isn't any more complicated than regular, really. If you mix it from basic chemical components it's a little more work, but entirely feasible in a home setting. If kits are for sale, which I expect, it's just as much or as little work as regular cyanotype. No real difference there.
The upshot is that you'll have control over what kind of paper (or whatever material you choose) you use. Watch out though. It's addictive...

 

[auburnxc]

I think my ultimate goal is to have success with an in-camera 8X10 pinhole cyanotype. That would be really exciting. I assume I will learn more about reciprocity failure along the way. I'm thankful that the people in this forum have been a wonderful resource so far.

 

[Vaughn]

There is also Cyanotype Rex. Don't know the important details, but it works by coating paper with just one of the chemicals and then developing it in the other...rather than mixing the two, then coating. Might use a slightly different form of the Ferric salt.

I'm guessing the ISO gets in to the single digits...

 

[nmp]

There is also Cyanotype Rex. Don't know the important details, but it works by coating paper with just one of the chemicals and then developing it in the other...rather than mixing the two, then coating. Might use a slightly different form of the Ferric salt.

I'm guessing the ISO gets in to the single digits...

More recently there is Doc Aetherman who has similar deconstructed procedure(s) that seem to be very fast as well:



"A simple process based on the chemistry of Cyanotype. The exposure time is shorter than Standard Cyanotype, even works with strong normal light instead of UV light."

:Niranjan.

 

[Petrochemist]

More recently there is Doc Aetherman who has similar deconstructed procedure(s) that seem to be very fast as well:



"A simple process based on the chemistry of Cyanotype. The exposure time is shorter than Standard Cyanotype, even works with strong normal light instead of UV light."

:Niranjan.

Thanks, I think I'm going to give that a try.
Typically it's the lesser used compound (potassium ferrocyanide) I've got excess stockx of, while I'm right out of the citrate...

 

[nmp]

Thanks, I think I'm going to give that a try.
Typically it's the lesser used compound (potassium ferrocyanide) I've got excess stockx of, while I'm right out of the citrate...

Please do report your findings if you get a chance to try out the process. He makes it look so easy, but I haven't seen anyone else mimicking it. I have been meaning to do it myself, but all the other projects keep getting in the way.... He has an another process that he demonstrates being able to develop an image with a "flash" exposure, but in that one he seems not to include the particulars.

Cyanotype Rex uses potassium ferrIcyanide instead of ferrOcyanide. I believe it also uses ferric oxalate. Mike Ware's book Cyanomicon, if I remember correctly, has more details. The way it is supposed to work with ferrOcyanide is that it reacts with the ferrous ions (formed from exposure) to make the insoluble Prussian white (ferrous ferrocyanide) which is then converted to Prussian blue with hydrogen peroxide. Normally it should react with ferric also to make Prussian blue but I think the extent of that is suppressed in absence of acidic conditions. Either that or it forms the soluble form that is washed out. So I think it is important to make sure the potassium ferrOcyanide solution is neutral. Otherwise one would get staining.

:Niranjan.

 

[Petrochemist]

Please do report your findings if you get a chance to try out the process. He makes it look so easy, but I haven't seen anyone else mimicking it. I have been meaning to do it myself, but all the other projects keep getting in the way.... He has an another process that he demonstrates being able to develop an image with a "flash" exposure, but in that one he seems not to include the particulars.

Cyanotype Rex uses potassium ferrIcyanide instead of ferrOcyanide. I believe it also uses ferric oxalate. Mike Ware's book Cyanomicon, if I remember correctly, has more details. The way it is supposed to work with ferrOcyanide is that it reacts with the ferrous ions (formed from exposure) to make the insoluble Prussian white (ferrous ferrocyanide) which is then converted to Prussian blue with hydrogen peroxide. Normally it should react with ferric also to make Prussian blue but I think the extent of that is suppressed in absence of acidic conditions. Either that or it forms the soluble form that is washed out. So I think it is important to make sure the potassium ferrOcyanide solution is neutral. Otherwise one would get staining.

:Niranjan.

It may be some time before I get round to it. My wife will probably be using it for sun prints long before I get round to digging out my antique glass negs, or sticking sheets in my 4x5 cameras. I'll try to remember to post a report here when I finally do.

Flash exposure should work well, especially if the UV blocking layer is stripped from the flash. Getting the exposure right will need trial & error (dark room test strip type techniques covering part of the paper & building up multiple exposures should help).

I have downloaded Mike Ware's book & browsed it on many occasions, but I've yet to try reading it properly. There is a huge amount to take in!

 

[cliveh]

Hello I am wondering how sensitive cyanotype paper is. I have been doing some experiments lately with cyanotype paper and I am just curious if it has a set ISO or if it can be determined.

Forget about ISO, as the formulation factors can vary more than the National Lottery and you just need to experiment.

 

[auburnxc]

My first attempt at pinhole in-camera cyanotype. 12 hour exposure.

 

[Donald Qualls]

Well, you've got something other than just the sun trail itself, so I'd say that's a good start. Traditional cyanotype? What size/distance pinhole?