Hullo Alasdair Heads Draftsmen in drawing offices used to draw plans with indian ink on starched linen. It was a pale bluish grey. This would be a semi transparent original called a 'tracing'. You could wash it out and have a piece of white linen. Copies could be made from this called 'blueprints'. The final image would be white on a mid or pale blue background. The process involved exposing a light sensitive coated paper to a carbon arc lamp which put out a high ultra violet light with the tracing in between. The print paper would then be run through a liquid or gas containing ammonia (I think) which would turn the exposed area blue and leave the drawn image as white. A later process used 'dyeline' paper which gave a black image on white paper and now Xerox type photocopiers are used with paper on a wide roll. I think your 'young Neil' might have worked in a dimly lit room adjoining a drawing office as a 'blue printer' and breathing in the gases. Bob Campbell in Brisbane, Aust.