Clay Harmon and Jon Cone disagree but I wonder if the divergence is due to different polymers -- they both use Jet plates that are designed for 350nm exposure. Clay says my 390-400nm lights that I use for kallitypes will not work with Jet plates. For now, I want to stick with Clay's process because I have seen his work in person and know that it is what I hope to achieve with photogravures.
Re single-point light sources: Clay and Jon both use 365nm light strips in exposure boxes. I chatted briefly with Clay about this. Clay agrees that a collimated source is best. But he observes that UV LEDs are fairly directional in their output, and he says that they work well enough for the application.
I am hunting for a solution that uses off-the-rack 365nm components. I see a 6x12-inch 365nm light on AliExpress that appears suitable for ganging up to cover a 12x18-inch print area. Any thoughts? Link below:
If others have come up with a suitable UV LED array, post here.
Sanders,
just noticed this thread - thought I would add a bit of what I have learned regarding burning photopolymer plates. When we were at Clay's workshop we used his custom "box". From what I remember about 400W of the cone 365 led strips. Clearly a custom set up, it worked very well with short exposures - 3min 30 sec was the standard time we used.
When I returned home I wanted to burn plates ( 43sm jet plates) locally. The studio I joined has an old black light tube assembly with 6 tubes ( ~4" spacing) about 6" from the glass cover plate. The studio used the unit for burning silk screens. I ran some small test strips using a 21 step Stouffer wedge. I was unsure how to interpret the results, so I asked Clay to run a Stouffer wedge on his unit for the "standard" 3:30 exposure. He very graciously agreed to run the test. He sent me the attached image of the result. As it shows - the highest clear step is 20 or 21 ( depending on your definition of clear)
Using his results as a bench mark I exposed plates at 15, 30 and 45 minutes on the UV tube unit and seem to get about a stop slower at 45 minutes. I made a 21 step wedges at 45 minutes using his color muse larger target and made a decent print, not quite linear but not too bad. Will use the results to adjust my quadtone rip profile. (I had used Clay's Epson 3880 QTR profile)
I wanted to see if I could get any kind of response with my Kallitype setup- which is almost identical to yours. I ran a few tests and the closest I could get was a "clear" 14-15 on the Stouffer wedge at 3 hours/45 minutes of exposure. For comparison my standard Kallitype exposure is 28 seconds. So the bottom line is the longer wavelength units will not work with the 43SM jet plates in any reasonable exposure time, based on my attempts.
The blacklight UV at my studio have a rather broad band of wavelengths with a peak near 365, but much less energy in the narrow 365 range, as indicated by my exposure of 45 minutes vs 3.5 minutes in Clay's unit. I will probably live with the studio unit once I get back to printing ( currently recovering from knee surgery). While the 45 minute is kind of long, it works since I can do other things (use the press) while waiting on the exposure.
I also did do a bit of searching for 365 LEDs to look at the most cost effective way to build a photogravure unit. Cone's strips are clearly the most efficient - actual 365 output vs wattage ( see test video on his page) however they are pretty pricy and require a custom box to implement. BTW Clay's box is extremely well designed and built ( as a retired engineer I was impressed with it). I did find these UV LEDs at 3 watts each, reasonably priced
however they would require soldering ( I am ok with that) and heat sink backing as well as a constant current power supply according to the comments... so it gets a bit complicated vs the simple 12 V strips for the cone strips or these -
https://store.waveformlighting.com/products/real-uv-led-strip-lights?variant=12527605219430
The UV 365 LED assemblies you noted look very promising, however it seems like the pricing/availability of these 365 UV LED keeps dropping, so I will probably hold off building a "burner" since I already pay dues for my studio membership and their UV burner seems adequate. However if you decide to try these units please keep us informed.
Thanks
Dave
