I love this technique. You need alot of time though.... days....it's very painstaking. Thin layers of pigment mixed with egg yolk and a little water built up over time - each layer ought to be dry before applying another.
I first did it at a course at the CityLit in London in about 1995. We mixed up all the ingredients (rabbitskin glue(!), french chalk over muslin...I think I remember) and made and prepared the board. Though I've more recently worked on ready prepared boards which is much quicker.
I remember a long time ago (when writing my college thesis on the Bloomsbury Group) reading about Vanessa Bell and Duncan Grant going into Lewes in Sussex in the 1920s to buy rabbit skin glue when they were decorating Charleston farmhouse (www.charleston.org.uk). There seemed something very earthy yet romantic about this - poor rabbits though! :-(