Potassium Ferricyanide Shelf life?

<p>Hi there!<br>

So I've been trying some Cyanotype printing for the first time and am having a bit of a problem:<br>

I've followed all the instructions in the "Blueprint to Cyanotypes" book I have, and tried various exposure times (up to 4 hours). The painted on solution seems to be oxidising as I can see the shadow of the objects in a lighter green (I've been trying photograms), while the fully exposed areas turn a dark green. However when I rinse it, everything gets washed away and I end up with nothing - just white paper.<br>

I've checked the troubleshooting guide in the book and can't see anything else I'm doing wrong, so I'm wondering if anyone knows whether Potassium Ferricyanide has a certain shelf life? The tub I have of it (in powder / crystal form) is about 10 years old and has probably been exposed to a fair amount of sunlight.<br>

The ferric ammonium citrate is brand new however, and I'm using watercolour paper out of a sketch book as the surface.<br>

From what I've been reading of this forum, you seem rather knowledgable about these things, so thought I'd ask! <br>

Any help much appreciated :-)</p>

 

<p>The bottle I have always used is at least 40 years old and still works fine for me. I got it from a chemist who had bought it about 1970 or earlier.</p>

<p>The shelf life of pot ferri crystals is almost indefinite if stored correctly (in a stoppered, brown glass bottle or away from daylight). If you are not getting the results then there is something else amiss. I use an 8 percent solution of pot ferri and a 20 percent soltuion of green ferric ammonium citrate. (Are you using the green variety?) I mix equal volumes of these. Exposure times in bright sun should be of the order of 15 minutes. In dull sun the exposure times can be hours but at 4 hours you should have more than you are getting. If there is no sun then put the paper underneath a fluorescent light, i.e. about 6" from the lamps and give it an hour or so.<br>

It is possible that your pot ferri has gone off with expsoure to light so if you can see nothing else which might account for the problem then buy a new bottle.</p>

<p>I would look at exposure (and light source), paper, and ph of your rinse water. 4 hour exposure? In sunlight? I've been getting good exposures in 20min under noon sun in the Mid-Atlantic of the US during the middle of winter. Using less than optimal artificial UV I've got nothing after 4 hours. Also, the process likes an acid environment. If your paper is buffered, you could get the fail you describe. Your tap water (if alkaline) could be a source of trouble. Try acidifying your water bath with vinegar or just develop in straight white vinegar.</p>

<p>there are two things here that could be going wrong. either the paper you are using is not allowing the chemistry to soak through or it is not being exposed long enough. i've been using the same batch of raw chemistry for years with perfect results each time. if you see the colors changing, then you know its working. i often leave my cyanotypes out for the entire day to expose (i mostly use paper negatives). the paper can only get so blue and if you are making photograms of opaque objects it might help. </p>

<p>you mentioned that the chemistry had been exposed to a fair amount of sunlight? what do you mean? what kind of container is it in? i always keep my raw chemistry in opaque plastic jugs. it doesn't matter if you take them out in the sun then. also, you NEVER want to expose raw pot. ferricyanide directly to uv light or to direct sunlight as the cyanide will be release and cause major problems. </p>