I have been wanting to experiment with chalk drawing for some time, so sitting here in the Observatory on the South Downs seems like a good time to start. Drawing with white on black can, at first, appear as if you are not drawing with colour; instead two polar opposites: positive vs. negative, light vs. dark. But just as there are two types of black in printing (single colour black, and then ‘rich black’ which is made up of all four printing colours: cyan, magenta, yellow, black), so working with white has its inflections too. CK Chesterton, creator of the priest-detective Father Brown, wrote a short essay on this, entitled ‘A Piece of Chalk’ (not to be confused (I did!) with Thomas Huxley’s ‘On a Piece of Chalk that I blogged about earlier), on how “white is a colour. It is not a mere absence of colour; it is a shining and affirmative thing, as fierce as red, as definite as black… Chastity does not mean abstention from sexual wrong; it means something flaming, like Joan of Arc. In a word, God paints in many colours; but he never paints so gorgeously, I had almost said so gaudily, as when He paints in white.” Morality aside, I question whether this would be the case in a colour blind world. Looking at great b&w photographs, the richness of the blacks and subtlety of the tones gives the feeling of colour; but is this like the afterimage left on the retina once you close your eyes? Could we see colour in black and white if we didn’t see colour elsewhere? What is certain is that in a colourful world chalk on blackboard offers a clarity and concentration that I really love. Thanks to Robert Krulwich for leading me to Chesterton. As it turns out, I have already been listening to his Radiolab podcasts, in particular the one on space. Worth checking out!