This covers many different methods, all with the intention of producing a complex pattern of colour reminiscent of marble. It can be with or without veining. There are usually chips of colour and lozenge shapes within marble due to its composite nature. Marbling is an intuitive painting process where you have several techniques at your disposal and you combine them in the manner you see fit. Here is one method I use:
You can also apply colour with an airbrush and work it with solvents.
This one I like a lot. Paint on a glaze in very dark green. Take a small piece of torn cardboard and scrape circular shapes into the glaze. Back up with a lighter colour green.
Similar to marbling techniques but with a more homogenous crystal-chip formation. There are no veins and the shapes can be painted on with layers of sponged on colour and some fine solvent spray work.
Again there is a great variety of methods. Essentially you paint on a glaze, wipe it out to form the grain shape, perhaps go over it with a flogger to create the little pits or checks one finds in genuine timber or detailing with a crossfire grain or figuring and then back up with the underlying timber colour. Achieving a convincing wood grain requires intuition and skill.
Sponges, Ragging and Plastic Bagging
Simpler methods of achieving an interesting decorative finish than the above, these are mainly single layer glazes applied or removed with the appropriate tool and backed up with a different colour.