Re: Wavelength for all Alt. Processes ?

Frank Gorga

My experience...

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.

--- Frank 

On Sun, Sep 5, 2021, 3:13 PM Michael <pixelwaster@...> wrote:
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.

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