This is what happens when you leave your marbling materials out all over the place and the kid wants to know how you made those pretty papers.
Step one. Apply apron. Assure him that it is not pink, it is "salmon".
Step two. Skim the surface of the bath.
Step three. Apply first colour.
Step four. Apply additional colours.
Step five. Stir and rake.
Step six. Comb then stir a little more.
Step seven. Have the assistant lay the paper, pull it off, and rinse.
Step eight. Admire the results.
Repeat, ad infinitum, or until the kid hears the The Wiggles show starting.