Apparently wax crayons and water-based finger-paints make REALLY nice atom diagrams.
:-) This reminds me of the other day when DS was tackling a 3D geometry question and was having trouble visualising it. He decided to make a model with plasticine, did so, saw immediately how to answer the question rigorously, and the next thing I knew he was bringing me plasticine robots and interestingly mottled cut faces of pladticine to inspect. Asynchrony, gottalovit.
(Well, makes a change from "bump above spam"!)