Sun as a UV source

[PVia]

Hi all...

Gathering info before getting started in alt processes and had a simple question. When using the sun as your UV source (pretty dependable here in So Cal) should the printng frame be out in direct sunlight facing the sun, or in open shade facing the sky?

I remember reading something about different contrast results in particular locations (full sun, open shade, etc...) so I'd like to know what y'all suggest.

I'll probably be starting with an Argyrotype process...

 

[dpurdy]

I have always aimed the print directly as possible at the sun. I love sun printing. I did read that you get a boost in contrast by printing in shade.

 

[bnstein]

I've tried both for cyanotype and apart from the difference in exposure time see no convincing difference. However cyanos usually take (me) about 10' in direct sun and self mask to an extent so over-exposure is not a massive deal. From what I gather argyrotypes need pretty standard exposures (http://www.alternativephotography.com/process_argyrotype.html).
You might also want to look at http://www.alternativephotography.com/articles/art068.html which is a summary of responses to questions about cyano printing. This leads me to the conclusion that it doesnt much matter which way you go, but that you need to get a consistent method that works for you.
As always with alt-process go forth and experiment my child!

 

[2F/2F]

Pasadena, eh? I was born at Huntington, and still live nearby. Let me know if you need to borrow any of my alt. process stuff. Not much fancy - just a few brushes, some chemicals, and a 20x24 Formulary printing frame. I also have the Christopher James Alt. Processes book, which you are welcome to borrow. I also have some VDB mixed, although It is about 6 months old now.

 

[Vaughn]

I have read recommendations for Salt prints to start in the sun and finish in the shade (or was it the other way around? or was that for cyanotypes?) Anyway, the idea is that the tonality of the final print changes for the better if the sun-stuck chemicals in the paper have some time to go all the way through their reactions...short intense exposures appearently do not allow for this. Terry King of Great Britian (and historian for the Royal Photograhic Society) has suggested the same thing for platinum printing.

I believe Christopher James mentions it also in his second edition.

Vaughn

 

[David A. Goldfarb]

For albumen the traditional sources say that one gets higher contrast with indirect light, and it seems to be true, but in my experience it is very subtle. It may have to do with how long the overall exposure time is--maybe after a certain length of time, it doesn't make a big difference, but for thinner negs with a short exposure time, maybe it makes a bigger difference. My best albumen negs print 20 minutes in direct light, 1 hour in indirect light, which is long, but it works for me.

 

[Kirk Keyes]

For It may have to do with how long the overall exposure time is--maybe after a certain length of time, it doesn't make a big difference, but for thinner negs with a short exposure time, maybe it makes a bigger difference.

Reciprocity failure being induced with the longer, shade exposures?

 

[Anton Lukoszevieze]

For salt prints I understand that northern light is best, not direct sun, but it depends on the neg. also, density, etc.

 

[David A. Goldfarb]

Reciprocity failure being induced with the longer, shade exposures?

I'm not sure. I don't think it's reciprocity failure, because the difference between direct sun through a window and shade is about two stops, and the time difference is also two stops. It may be the reaction time issue that Vaughn mentions.

 

[Kirk Keyes]

I'm dubious of "reaction time". It should be a very fast chemical reaction.

 

[Vaughn]

I'm dubious of "reaction time". It should be a very fast chemical reaction.

I read up on it a little...In Christopher James' 2nd edition of Alt. Photo. Processes (p162), Mike Ware suggests that by slowing down the exposure, the print-out is allowed to progress to a greater degree than with quick hard exposures -- thus increasing the the self-masking.

So it is not so much the "reaction time", as the non-instanteous creation of the print-out image.

A more intense print-out image would help to retain shadow detail while the highlights progress. If this is what is happening, then it might help with other processes that have self-masking, such as salt prints and platinum/palladium prints.

Vaughn

A test of this theory could be done by giving a cyanotype a short hard exposure, check out the print-out image, then put the contact frame in the dark. Five minutes later, see if the print-out image has increased while it was in the dark.

 

[David A. Goldfarb]

The self-masking property does make this all the more confusing. Say that one method causes the shadows to come in faster than the highlights--then the masking property takes over, and the highlights will continue faster than the shadows. This happens in both direct and indirect light, but maybe the rates are different. It's very hard to say what one is comparing at that point, because you can usually just wait until the highlights are where you want them for the contrast you're after, with albumen at least.

Some have speculated that it has something to do with the Callier effect, but I doubt this, because I'm not convinced that the Callier effect is that important with a contact print, and because if it were the Callier effect, there would be more contrast with direct light than with diffuse light, and it's in fact the other way around.

 

[Vaughn]

David -- it may not a matter of the shadows coming in "faster" with one method over the other, but instead the darking of the paper due to the exposure (the print-out) lagging slightly behind the actual chemical change created by the striking of the chemicals by the UV light. Chemical reactions are not instantaneous -- they happen at different rates (tho some happen so fast that they appear to be instantaneous to us slow minded folks.LOL!) So I can picture electrons of the iron compounds being knocked off as the UV hits them...and this happening at a constant rate creating the exposure...but then it taking a little more time for the electrons to settle down and the chemicals to order themselves into new compounds.

Well, I am probably just blowing smoke out my nether regions, but it is a fun metal exercise.

Vaughn

 

[Gustavo_Castilla]

My 2 cents !
When using the sun you will get a higher contrast the down side is that it is rather difficult to get the same results a few days latter as exposure time will change , one of the more important things to consider is the radial heat ( how much heat your frame absorbs ) as this will change the exposure time and the ability of the chemistry to register gradation and contrast . and it is exponential buy the power of two .
this means that as the frame gets hotter it drys the emulsion and it takes the power of 2 to generate an image .
for example :
first exposure bright sun mid day = 5 min exposure ( 75degrees at glass)
second same conditions but glass is 95 degrees exposure will be 10 but it wont match the first one as the radiant heat and radiation affects the chemistry on the paper

 

[reellis67]

My 2 cents !
When using the sun you will get a higher contrast the down side is that it is rather difficult to get the same results a few days latter as exposure time will change , one of the more important things to consider is the radial heat ( how much heat your frame absorbs ) as this will change the exposure time and the ability of the chemistry to register gradation and contrast . and it is exponential buy the power of two .
this means that as the frame gets hotter it drys the emulsion and it takes the power of 2 to generate an image .
for example :
first exposure bright sun mid day = 5 min exposure ( 75degrees at glass)
second same conditions but glass is 95 degrees exposure will be 10 but it wont match the first one as the radiant heat and radiation affects the chemistry on the paper

I only have the sun for printing historic processes and I can say that these are very valid points. The results I get are always different, which is both good and bad. Sometimes I get a nice surprise and sometimes I have to stop for the day because I just can't get a good print.

- Randy

 

[snallan]

As an aside on the reaction times for the chemical reactions for formation of the image. Whilst the reactions themselves are fast, they are not occurring in solution where the photoelectrons produced can move freely to react further, reducing metal ions to image metal. The sensitiser is adsorbed onto the paper fibres, so diffusion of reaction products will become limiting in the overall image forming sequence - as Vaughn says, the print-out lags behind the actual photochemical reaction.

 

[Vaughn]

FYI...

I was up all night making platinum/palladium prints. My exposure times were very short -- 2 minutes to 9 minutes, depending on the neg. (on COT320, warm Pot oxalate)

Just for fun, I gave the neg & paper half its exposure time, rested the paper for 15 minutes, then continued with the rest of the exposure. I suppose I should have done it both ways to see the tonal difference between printing straight thru and resting the print halfway thru, but I only had so much time and so much paper and chemistry.

But what I did notice was the amount of POP image (the border around the negative) when I took the printing frame from under the lights halfway thru exposure -- and visually compared it to what I had 15 minutes later (I just turned the printing frame face down on the table.) There was a very significant increase in the amount of POP image after the 15 minute rest. So, depending on the amount of self-masking the POP images does, allowing enough time for the POP to print itself should have some affect on the tonality of the print. The prints did look nice...

Vaughn