I decided to try experimenting today and have been working on MDF (I had it cut to size at B & Q).
In my studio, I coated it with purple acrylic (no reason, really, it was to hand) and then drew a landscape with a pastel pencil; I then blocked in colour with gouache, putting details in with chalk pastels and pushing the colours around in both media with water. I liked the effect but decided the textures created by the initial acrylic layer are too rough and took sandpaper to them.
I worked for a while longer into the sky, and now think I’ve ruined the painting altogether. The only answer is to use water to effectively rub out the clouds and start on that bit again.
I wrote that yesterday and when I came in this morning, having allowed time for drying, I was relieved to see the sky looking much better. A little bit of fiddling about, and I think I have a finished painting. Chalk pastel mixed with water is rather fun.