POP contrast Quandry

I printed an image last friday that, in my opinion, sings. I took notes and did everything exactly the same today but the image does not look the same. IN fact it is quite a bit flatter in contrast. Here is a description of what is different. Maybe someone can tell me why.

Last friday's image never really bleached to an orange color, today it did.

The final dried image from last friday is a very pleasing dark plum and is punchy. Looks like it just came out of the printing frame. Not the chocolate I have come to expect. Todays is chocolate

Here is the process
Expose to the right color 8-10 minutes
Fix in 1:11 Nacco NU FIX five minutes in two baths
Selenium tone 2% for 2.5 minutes

Wash for a long time

Any thoughts would be nice

Was it exposed in the same light? POP has such a long scale that it is very difficult to get the same exposure twice by just judgng the print before processing.

Did you wash before fixing? If so, did you wash for the same time at the sam temperature? If not, why not?

Was the fixer new? There's a tremendous amount of silver in POP, and the fixer exhausts very quickly.

Same with the selenium toner - KRST (was that what you used?) depends on a certain concentration of ammonium thiosulfate to work - underfixed POP would kill that very quickly.

I have only used Tetenal Gold toner myself - very nice, and the result depends on whether toning or fixing comes first. So incomplete fixing is immediately obvious, at least with post-fix toning.

I am using Kodak's rapid selenium toner. Temperature may be the issue. There is no way to regulate the temp of the water in my sink so I do my best to get the temp to 68 degrees F before I start and from then on it is a crap shoot as to what comes out. after about ten minutes. For the one minute initial wash I have the water at 68 dergrees. I let the fix and toner come up to room temp before using and that is about 73ish degrees.

Both fix and selenium are fresh. Would water temp in the intial wash make that big a differentce? I am exposing using sun light could that be the problem?

What would explain the paper not bleaching on last friday's printing?

All I can do is suggest some of the factors I believe are influencing my POP prints

Water temperature influences solubility and mobility of the excess silver nitrate, ths determining how much of it gets washed out in the initial wash. Any AgNO3 left in the paper will "use up" the fixer before it starts on the chloride.

I don't know Nacco NU fix, I use a lump of sodium thiosulfate in a tray of water... No precision, but then I do it all by eye anyway. I usually tone before fixing, which helps.

I don't know what your sunlight is like, but what we get here in Norway is very variable - if we get any at all. With weaker sunlight a longer exposure is needed, which AFIK tends to increase contrast - reducing apparent bleaching.

I was playing around with POP quite a lot this summer, since it's much nicer to make prints in the sun than in the darkroom that time of year. I still don't claim to understand anything at all about the process, except for the simplest basics.

Thanks, I'll keep playing.

I have absolutely no knowlege of POP so the following is something I have read/heard and therefore maybe way off scale or just plain wrong!

The contrast of POP prints can be changed by exposure time. I'm sure I read an article this year in Black and White Photography (UK) but I can't find it. So maybe your problem maybe a difference of the quality of the UV from the sun; e.g. different time of day.

Just a thought.

Mark, can't really add much but can relate what I have seen recently while attempting to do some Ziatype palladium prints (which is a POP). Before I built the UV unit, I was using the sun and that was a BIG deal, time of day, location of sun, any clouds all seemed to influence what happened. Thought that things would be a lot easier after I started using the UV light source, but NOooooooo!!! Found out how much influence HUMIDITY has on the overall process. If memory serves me right, there was a Pacific front that passed through here on Monday that might have been passing through your area around Friday of last week, while you might not have seen much change, the paper/process seems to pick up on every little thing, so that is another possibility.

The experts in this area might be able to give you more information - know I plan to pick up one of the temp/humidity monitors that Radio Shack sells just so I can document those variables when printing from now on - along with a long list of other variables..

But isn't it fun? I think so...keep us posted.