Back in the olden days, when the sun shone every summer and when kids were happy with a mouldy orange for a Christmas present, photography was partly a chemical process. After you had carefully clicked a shutter - and, be careful, film costs money you know - you would disappear into a dark room and start mixing chemical solutions in the pale glow of an amber lamp. Sometimes things could go wrong, and if they did, there was no "undo the last action" command. You would occasionally be left with negatives that had strange markings, grain that would gather together in the manner of congealed soup, and shades of grey that were even more bizarre than an erotic dream. When it came to the enlarging process, you would often pass such negatives by - they weren't worth the investment in expensive bromide paper and developing solution. What the hell, you would think, I will leave that one for fifty years until I am old and locked down, with nothing better to do than to rescan the negative, remix the colours, remaster the grain and remember the days when Halifax had mill chimneys punctuating the sky.