Sorry, but you have got me fired up now, as I would love to give this talk - You probably wouldn’t have the facilities to do a demonstration showing the production of a photogenic drawing, but if you could they would all be hooked. If you made an exposure using the same chemistry as used by William Henry Fox Talbot in 1834 and showed them the wet result in the light of day, the effect would be incomparable with anything digital. The wet coloured image will reveal a superb colour and contrast that even when stabilised, will then change before their eyes in 30 seconds or so.