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I went with blacklight LEDs in my revamped exposure unit. They’re in the 380-390 range. I went a little overkill but I wanted to ensure even coverage for the largest possible prints I could make- I can go up to 16x20. So I have 16 strips of 22” length. My exposure times are 2 minutes now, down from 12+ with fluorescent bulbs, and more consistent. I’m printing palladium mostly at this point, with the odd cyanotype thrown in. Will be doing gum over pt/pd in the near future.
On Sep 6, 2021, at 9:13 AM, Frank Gorga <fgorga@...> wrote:
Processes that use the photo reduction of iron(III) to iron(II) are broadly sensitive to light at around 390 nm. Thus they work just fine with inexpensive BLB bulbs/LEDs. These sources also seem to work well for salted-paper.
Photopolymer gravure does not work with the BLB sources, as it requires the shorter wavelengths of the more expensive 360 nm sources. I have no information on how the 360 nm sources work with the iron based processes, but they do seem to work for salted-paper.
These days I use a simple plywood box with four strips of inexpensive, pre-wired BLB LED strips which gives me 10 or 15 min exposure times for cyanotype and salted-paper.
The nice thing about BLB LEDs is you don't need to really worry about managing the waste heat. My box has a few vent holes leftover from when it had fluorescent bulbs but no fan. It barely gets above ambient temperature by 15 min.
I used to have a nice list of what range of light worked with what process. I suspect it is on the drive that died.
I am looking to make a new one because I've seen youtubers use everything from 360nm (monochromatic) to white light from a 500 watt tungsten spot. they all have short (<15 min) exposure times. I just would like to make an exposure box with the right light to start with.