Epson 1430.
Standard factory inks.
Exposure table was a vastex with fluorescent UV bulbs, at about 4 minutes, with a Saati Textile PV emulsion.
The full-color test print on waterproof inkjet film was not done with any halftones, so the resulting screen is not usable, just did this a while back as a test to show how much of the spectrum of colors from the factory inks is blocking the UV.
Point is you can print just Yellow and still get a good UV blocking... UV block has nothing to do with "what your eyes see"... like the whole idea of "is your film dark enough"... it only has to be dark to UV light - hence the original post.... just sharing that I have tested the same and you can see through a lot of that full-color transparency, but just like rubylith - the red to yellow to green areas are using enough yellow ink to block the UV. The Magenta and Cyan inks don't block it much (because of their color they are allowing blue and uv light through) -- and the black ink does block UV. So usually if you print black and yellow it does a good job, or just full rich CMYK and it burns halftones a bit better than just yellow or just black etc. But you don't need to change these printers from full-color into just-black in order to make UV blocking screenprint films for exposure... and you don't need a RIP etc... just a way to convert images into halftones, and set your printing colors of those halftones to rich-black 100% cmyk for example.
Looking at the pictures again... the opposite is actually true... the Blue "looks" darker than the yellow, but the blue cured and the yellow blocked the UV and washed out.
The proper exposure really has to do more with the ratio between the actual UV blocking % for the amount of time you are exposing and for the power amount of UV in a given area being blocked, versus the clear areas allowing light.... usually you are going for a high-contrast between the UV blocking and the clear areas and with enough power based on the emulsion used for long enough to get a positive cure through both sides strong enough to hold up well to washing (even power washing if you can) and have the uv-blocked areas wash out easily (not with lots of effort as if they are semi-cured).... so all the variables have to really work together...
I tried a just-yellow print at the shop I am working now which uses an amerigraph with a 1200 watt metal halide I think, and even for a minute or so the power of that UV compared to the vastex fluorescent bulbs was enough to still get through the yellow... but the rich-black printed using 100% CMYK values makes a dark and clean high-resolution film off the epson 1430 that does work great on that higher powered MH table... so there is something to the ratio of the amount of UV being blocked by for example the yellow or the black, and probably more when a rich-black is printed. The actual density of the black to UV light is not as important as the actual ratio of those 3 or more factors involved - emulsion, dark/clear ratio, power/time ratio, etc.
Fun stuff!
