When doing a demonstration I always practice beforehand. For this demo I actually did two drawings - one fossil on paper and one landscape geology drawing on plywood. So the practice runs of the fossil were interesting to me. Much like the crystallised rock I did for the schoolkids a while back, each round of re-doing the drawing resulting in something slightly different. In the actual live demonstration I ended up focusing on the dark/light contract of the spiral rings, which really didn't grab my interest at all in the practice runs!
It took me years to understand why some artists repeated their subjects - think of Monet's waterlilies or haystacks for example. It's because even with the same subject you always find something different to express.
All the sketches are pencils on newsprint.