Platinum Printing: The Constant Humidity Box (Part 2).
Right, now that the rather rough design formalities are out of the way, on with the fun stuff!
Please note that this is a bit of a work in progress, I've no idea if it will work as planned. There may be problems and alterations down the road, but that's part of the fun of invention. From a personal perspective, I get a huge amount of satisfaction from trying to invent my way out of problems.
Platinum Printing relies on a willingness to knock together tools, think laterally and glue together solutions. You simply cannot pop down to the shops and buy a constant humidity box. Jessops don't do alternative processes, hell, they barely do film anymore. Anyway, I appear to be rambling. I'll finish this bit with the words of that Greek chap Plato, "Necessity is the mother of invention".
The Box.
After ten minutes spent thinking about the construction of an airtight box - varnished wood versus fibreglass construction - I came to the conclusion that it would be quicker, easier and downright cheaper to simply buy something suitable for the job. A quick trip to Homebase secured an 80 Litre plastic storage crate that measured up quite well.
My Platinum Printing efforts are currently limited by the cost of the emulsion and the size of the paper I can fit in my 14" x 12" developing trays. This means that my maximum print size is 25cms x 30cms. This 80 litre crate is more than big enough for the job. For those of you interested in the specifics, the crate is made by "Whatmore Creative Plastics" and the model (if that's the right word) is called "Fusion".
Laser Guided Measuring.
I'm officially useless with a tape measure. Every time I go near one I hear the voice of an ex-housemate intoning the wise words "Measure twice, cut once!" (you know who you are... Scoles). But honestly, I can measure something three times and get three different results. Perhaps it's wishful thinking, but I often settle on the biggest... Annnnyway... Thankfully science has come to my rescue!. Lasers are ace!
Now, some might argue that the use of several hundred pounds worth of Leica laser measuring technology is overkill for such a shed born project. But I've got a laser and I'm damn well going to use it! In this case the laser proved really useful. It'll measure from the base of the unit to wherever the laser dot falls and as the sides of my crate taper towards the bottom the laser made quick work of an otherwise fiddly job. The only important point was using a little bit of black insulating tape to stop the laser beaming through the crate and returning a false reading.
Cut, Drill, Countersink and Glue.
My design calls for the construction of two frames. The bottom frame is there to stop any paper from accidentally falling into the salt solution that's going to slosh around in the bottom of the crate. The top frame is going to be used to suspend the printing paper. The bonus of buying an off the shelf plastic box is that I could select one with tapering sides. This in turn means that the frames will friction fit without needing to be glued in place.
The only really, really, really important thing is to make sure that you accurately measure the internal dimensions of the crate at the height at which you want the frame to sit. If the frame is made too small it will slip further down into the crate than you intended. If the frame is made too big it will either sit too high, or it won't fit in the crate at all (more on this later...).
With accurate measurements taken with the Laser(!) I confidently set about marking up and cutting the frame material. My Christmas list now includes a request for a Laser(!) that can cut stuff, but for now I have to stick with a mitre saw.
I haven't made a conscious choice in the wood that I've used, it's simply left over timber from another project. Now this may cause me problems further down the line, but by happy chance I've ended up using Cherry wood, which I've read is pretty stable, so fingers crossed! For those of you keen on the numbers the wood is 2cm x 1cm beading and the frames outer dimensions worked out to be 30cm by 49.6cm for the bottom frame and 34.6cm by 54.2cm for the top frame.
Given the high humidity I'm hoping to generate within the box, I wanted to avoid using metal that would end up rusting away to nothing. After a little lateral thinking I figured that drilling each frame at 2cm intervals would allow me to weave a mesh that would act as a safety net in the bottom frame, and a washing line type affair in the top frame. You'll notice the old-school tape measure... You would not believe how long it too me to mark up each piece of wood...
After a good old blast on the pillar drill (every kitchen should have one), I ended up with a pretty sweet wooden Meccano set...
I'm not usually one for aesthetics, but for some reason I had the urge to countersink the holes to make them look tidy. What started as an urge soon turned to regret once I realised just how many holes I had to drill out (on both sides of the wood...).
So, after cutting, drilling, countersinking and then sanding, everything was ready to glue and clamp. Now I'm a big fan of tools and the band clamp pictured above is by far the best tool I've brought in a long time. It allows you to apply firm, even pressure around your job and makes it really easy to ensure that you have everything square and level. The downside is that I really need two for this project. Only having one clamp slows things down a bit as the job needs to be left to dry overnight.
Threading the Safety Frame.
Twelve hours later and the bottom frame has dried nicely. A quick sanding to remove any excess glue and the frame is ready to be threaded. I thought long and hard about the thread I intended to use. I wanted to avoid anything that might wick the contents of the salt solution out of the bottom of the box and endanger the paper. But at the same time, the thread needs to be able to support the weight of any paper that might accidentally comes loose. In the end heavy duty nylon seemed like the best bet. It's strong (the breaking strain is something like 9kg, far more than necessary but comforting nonetheless), and because it's not a woven cord it's unlikely to soak up any salt solution.
Weaving complete and a quick test fit confirms that the frame sits nicely at the expected height above the base of the box.
The Anti-drip Lid.
One of the concerns that came up during a discussion with my partner in crime, was that of condensation forming on the underside of the box's lid. Removing the lid to gain access to the paper might inadvertently shower the paper with water. Not good. After a little lateral thinking we came up with the idea of securing an absorbent pad to the underside of the lid. I wanted to steer clear of gluing anything in place, so instead came up with a way of threading the lid to suspend the pad from some of the same nylon used in the safety frame.
A hot pin made quick work of creating the holes through which to thread the nylon...
The pad itself is made from a left over section of archival mount board cut to size.
The board is then covered in two layers of cotton muslin fabric cut big enough to wrap around the board. Again, I want to avoid using glue or tape that might degrade in high humidity.
After wrapping, the pad is wrestled into place under the nylon. The advantage of this approach is that I'll easily be able to clean / replace the fabric if it becomes dirty.
The Paper Hanging Frame Disaster!
A day and later I was able to remove the top frame from the clamp. Excited to be nearing the end of the build, my heart sank as I attempted to place the frame in the top of the box. Too big. Damn.
How could this have happened!?! I used a laser! I measured twice, cut once, and everything was going so well. Damn.
Ahhhh, the corners, of course. In my heady rush to play with lasers, I neglected to consider that the corners of my box are rounded at the top and far less square than those at the bottom.
Well, there was nothing for it but to attempt to 're-engineer' a solution. With the frame placed as far into the box as it would go, I marked out a cut to the left of the nearest threading hole.
Now for the delicate bit. Cutting the frame at this point was risky as the only thing holding it together is wood glue. A book was used to support the frame and hold it horizontal.
Fingers crossed...
Success! Two very careful cuts have separated the frame as shown above
Ok, so it's not the neatest of jobs, but the cut ran as closely as I could get to the threading hole and the wood didn't split. As far as I'm concerned, it's a win.
Right, now to get rid of the pesky short bits. More very careful cutting...
This is going far too well... Two more careful cuts have freed the side of the frame that I need to keep. The alteration has shortened it by about 1mm though, which is going to knock the frame slightly out of square...
Having said that, laid out on the bench the frame looks promising.
Back into the bandclamp with a liberal coating of wood glue! Working on the principle that more glue equals a stronger joint, I revisit the frame a couple of times during the drying period to add a little extra.
A set square confirms that the frame is slightly out of square, but not by much. Nothing I can't live with.
The quetsion as to whether it fits is happily answered with a yes!
Final Threading and Finishing Up!
With the paper hanging frame installed, all that remained to do was simply thread it with nylon cord.
With the help of some mini wooden pegs (thanks eBay!) the paper is hung...
And there we go! All done! I'll report back on it's effectiveness once the box has been used in anger.
