Ilfolith IH4 questions

[Discoman]

okay, I just got a box of this film, partially used.
ran a couple sheets through paper developer, no fog appeared.

but what I cannot find anywhere is this:
what is the ISO rating of the film? I was guesstimating around ISO of 6
but my camera doesn't really offer a setting for ISO6, so I was going to shoot it at ISO4.
now, if I have the actual rated ISO, that would be helpful.
and if I am forced to shoot it at 4, should I just tell the lab to process at 4, or to be pulled from 6?
and, as i'd probably go to dr5 for processing, what developer should be selected for the true high contrast lith film look? or will it need to be in special instructions to be processed as a lith negative?
thanks.
i've never used lith film before, so i really need the help on this.

[Mark Sampson]

Graphic-arts films like these generally didn't have ISO speed ratings listed; they were not meant for 'normal' or 'pictorial' photography and the usual speed ratings just don't apply. The high contrast and ortho, or blue, sensitivity would make a true ISO speed difficult to determine, even if the manufacturers ever thought you'd use films like this outside the lab. Not that you can't find out an effective EI for your working method; you're just going to have to test for your particular application, just as you would if you were using it in the darkroom.