Masking transparencies

[Supertom]

Used, how?

Use it as a cheaper , non toxic liquid mask. Put it on , paint. Wait for paint to dry and then remove masking under running tap .

I noticed you didn't include Vegemite, but then again you said "non toxic."   

But seriously, Rickshaw, have you thought of using laboratory film?  In the US the brand name for it is Parafilm M.  You cut out a roll, stretch it out a little, let it shrink back for about 30 seconds, then apply on the area you want to mask.  Then burnish it down with your finger, and cut off.  Takes some practice, but quite effective and a roll will last you years.  It even works around compound curves.