Many thanks Vaughn / Philip,
Apologies if I was economical with my words, it was late last night when I posted the question.
I think you have really both answered my question. The background to this was that when I made up my first batch of goop, I coated using 1mm magnetic strip as guidance. Picking up the semi dried Yupo sheet after coating, an elephant of doubt wandered into my head. I mistakenly began to think that the tissue coating was too think, probably because it felt so bloody heavy! Anyway I scraped off the semi dried goop, reheated it and coated again but much, much, thinner, paint brush thin. Apart from the fact that reheating a second time probably gained a degree of goop concentration, my initial exposures resulted in no image at all (5-25min) and tissue that didn`t want to release, so probably over cooked. Don`t bother commenting, I`II be back to cooking up fresh goop and recoating with the magnetic strip and yes I`II do the volume math too!
Back with more questions later no doubt!
Cheers Mat