Platinum Printing: The Constant Humidity Box.
Platinum Printing is tricky. Actually, tricky is probably an understatement. There are so many variables in play, printing can often become a bit of a lottery. Have you managed to secure a good batch of paper? Because this new batch may not perform in the same way as the last batch... How about your chemistry? How old is it? Have you filtered it recently? Is it at the correct temperature? Speaking of temperature, how cold is it in your basement darkroom at this time of year? There's snow on the ground outside, that must make it colder in here, right? Everything I've read, combined with my own albeit limited experience, points towards consistency being the key in Platinum Printing. If you can control as many as the variables as possible, you stand a better chance of being able to produce predictable, consistent prints.
One of the biggest controlling factors when Platinum Printing is the Relative Humidity of both the environment you work in, and the materials you work with. Everything I've read (and have yet to put into practice), points towards humidity being a pretty hot (and wet) topic. Being able to control the humidity, specifically that of your paper, appears to be key in producing a good print.
Controlling all of these variables is always going to be an issue of scale. I'm currently working out of a university darkroom, located in the basement of a nineteenth century building. There's no way I'll be able to control the Relative Humidity of my entire workspace. The equipment I'd need is way out of my price-range and I'm already making enough of a nuisance of myself by tying up a pretty large chunk of communal space. So instead, I've decided to think smaller and concentrate my efforts on building a tool that will help me control the humidity of my paper. With that in mind, ladies and gentlemen, may I present the Harrison (Mark 1) Constant Humidity Box...
Design.
I take a pretty 'Heath Robinson' approach to design. Napkins make the best sketchpad, measurements are accurate to the 'ish' (as in 50 centimeters... ish.), and the only certainty is that the final result will look nothing like the initial concept. Garden shed engineering (or in my case kitchen table engineering) made England great, so it's on with the lateral thinking caps and away we go!
This design is based upon the principle of creating a known relative humidity through the use of a saturated salt solution. The science is best explained here, suffice to say that by part filling an airtight box with a solution that generates a known relative humidity, we can roughly control the humidity of the material contained within said box.
There are three things I'm certain this project will require. 1: A pretty air tight box. 2: A frame to suspend the printing paper from. 3: A safety screen to stop accidentally dropped paper from falling into our saturated salt solution.
