For this, I've used a cheap $2 plastic photo frame that I've cut down the length to fit neatly into the UV lamp. In this is (from the top)
- Glass (which I broke the corner off, cutting it down to fit the re-sized photo frame. OK, I suck at cutting glass)
- 1 sheet of rapidraw film, just to diffuse the UV light a little
- The artwork
- The copper board with photosensitive film
- A sheet of A4 paper, folded, to give the sandwich some more thickness
- The cut-down original backing plate of the photo frame.
It looks like this.
So this assembly goes into the UV lamp, like so:
I'd previously done an exposure timing test with the film, but not with the film on copper board. The exposure test is done by progressively covering sections of the film, and determining which section has been exposed sufficiently where the artwork is clear, but not exposed where the artwork is dark.
Too little exposure, and the film won't harden enough (with negative film, the exposed areas of film harden)
Too much, and the areas that shouldn't have been exposed may start to harden. This is why the artwork contrast is very important.
OK, so prior experimentation indicated that about 2 minutes should be enough. With this test board, I had three identical patterns, so I exposed one section for 2 minutes, the next for 2:30, and the last for 3 minutes.
This is the result:
|From left to right, 3 min, 2.5 min and 2 min exposure|
|3 minutes on left, 2 minutes on right|
The actual development of the film occurs pretty quickly (it's more of a "stripping" of the un-exposed regions), and I'm not sure yet what occurs if the film is over developed.
Next time, we'll see what the copper etching reveals...