Exposing in the Sun
Solarplates are most sensitive to a range of UV light varying between 350 nm and 370 nm, with a peak at 360 nm. Soalrplates also have a 'wide latitude of exposure', which means that the polymer is insensitive to small variations in intensity of UV light, so light cloud variation not a problem.
Best to expose on sunny days or days with constant cloud cover. Expose from late morning to mid-afternoon when the UV intesity is least variable for more control. Outside of these times the intensity is changing rapidly, so by the time you have made a test strip, the intensity of the light may well have changed.
In very hot weather the plates can become very sticky, and can harden without an image forming in extreme hot weather. With experience you can estimate exposure times accurately despite daily and seasonal cycles. Exposure times can vary from as little as 30secs in mid-summer, to 30 mins in midwinter, depending on where you live. Use test strips!
The Stouffer Wedge is a small grayscale transparency available from photographic suppliers. We use 21-step wedge. To use it cut a small strip of solar plate slightly larger than the wedge, remove the cover film and dust the strip with talc. Expose the wedge for a given time (use non-emulsion side to contact the plate). Expose for, say, 2.5 minutes and develop for a fixed time as well, say 3 minutes. Examine the strip to take a reading.
Under the most opaque steps of the wedge the polymer will completely wash away; under the lightest steps the polymer will harden; while several steps in the middle will only partially wash away. Observe that the numbers 2 to 21 will form in relief, keeping mind that they will form in reverse if you keep emulsion side up). For a reading all hardened or partially hardened segments are counted as solid and the highest numbered step that remains solid provides the reading. E.g. if you find that 2-9 are solid, 10-11 are partial, and 12-20 are completely washed away then 11 is the reading. We have found that best results for drawings and photocopies is a range between 9-11, while opaque film, such as laser and photographic transparencies will work well in a range of 12-14.
Exposing Indoors
Sunlamps, because of their shape, can expose plates unevenly, though can be useful for small plates. (what is small?)
Making your own lightbox for 12x16" plates:
- 14x18" board, 0.75" thick
- six 24" standard strip light fittings
- six 20W blacklight UV lamps (360nm)
- screws
- switch
- blackout lining fabric
- Pack together lights on board fairly firmly
- Make sure they are oriented the same way so electrical fitting are at the same end
Can balance the board on bricks. Ideal height from plate to lights is about 8". In this setup around 1 min for screen and 1 min for transparency are good starting points. Corresponding grayscale reading is 11. Artificial lights can lose power after many hours of use.
Problem solving
Poor contact in contact frame arising from poor technique in cutting plates, can result in patchy and faded images. If there is any warping the film will not sit flat against plate.
Can also encounter poor contact if transparency is glass or thick film, or film with thick application of drawing media. Also don't want transparency larger than the plate.
Largest size of plate you want to work with is 16x20", start small.
Commercial units
Need a timer.
A good commercial unit will have metal halide lamp, vacuum frame and can handle larger plates.
Vacuum can cause problems if seal is weak. Can also cause air bubbles in transparency/plate contact. Use roller to remove them.
