I figured just like with digital cameras, in a consumer product you can't remove all susceptibility outside the visible spectrum, just have several stops of difference in sensitivity.
R72 Filter used, +14.5 stops of 'filter compensation' to get this effect, or EI 0.017 from a ISO 400 film (I should mention this included 2 stops of reciprocity correction, but its just guess work at this point).
Exposure was f/2.8, 15 seconds, correct unfiltered exposure was f/11, 1/400th.
I was considered lowering the pH level of the C-41 developer to effectively underdevelop the reds, but the reds dont seem that dense as I suspect they would be, they seem quite godo, but the green and blue channels have a thin density range.
Needs more exposure, with a green and blue filter, would probably help a bit.
Defniately seems to be an IR effect their to my eyes.
Film was ISO 400 35mm cheap unknown brand film, unknown age.
Scanned with levels set on each colour channel to not have any clipping at all, then auto-levelled to provide a 'balanced' image (regardless of false colour) to see the effect.
Test #2 will include the colour filters and increased exposure.
A high contrast film may be much better for this, less expansion of green and blue would be needed, hence less grain contrast, and less shitty scanner noise, perhaps Velvia etc.
