Here are the edges and the recipe. The first thing i did was paint the tracks with a very dark brown mix, nearly black infact. Then a light over spray with Tamiya flat earth XF-52 in a random pattern followed by the pastels. I use standard chalk artists pastels from the art shop that I grind up into dust. I used three colours here, a bright orange, chocolate brown and black that I mixed into 3 little piles. The first 50/50 orange with chocolate the second a 50/50 chocolate and black and the final pile was pure orange. I started with the choc/orange colour mixed with lots of water, I dabbed it randomly over the entire track. I did the same thing with the choc/black and by the end of it over 85% of the track had been hit with the diluted pastel mixes. Now comes the orange colour, this I diluted much more than the other colours, much much more. I kept the orange to the edges and between each link then I dobbed a few sparse random splashes on the tracks themselves. Voila.