Film positives are opaque images printed, painted or drawn onto transparent or translucent materials which are used to make stencils in screenprinting. Here's a quick tutorial on how to make cheap film positives by rubbing regular laser print outs from a copy store with vegetable oil. Printing onto acetate or mylar can be expensive if you can't do it yourself (Standard Screen Supply charges $15/sq ft), so this can be an inexpensive and fairly effective alternative.
For awhile I was using coated acetate sheets that absorb inkjet printing for my positives, but since most consumer-level printers only go up to 13"x 19", any image larger than that would require tiling the sheets, which is a difficult and time-consuming thing to do with photographic work.
So I made a trip to the Park Slope Copy Center on 7th avenue, which can laser-print b&w up to about 30"x 40", and got (4) 17"x 26" images printed for about $6.50 total. Rubbing bond paper with oil makes the paper translucent without degrading the printed image (with inkjet I'm not so sure) but just make sure that every inch of the paper is rubbed in in order to expose properly. I trimmed down the sheet shown in the video before exposing.
