Often during a project or after completion of a challenging oil painting an artist can feel a little burnt out. It seems strange to say this, but painting is work too. Good work, but like anything one does for a time there is a need for a break. I find that doing quick studies with no fixed idea on the outcome helps me to unwind. The spontaneous approach gets the passion going again.
My medium of choice for these interludes is watercolour and pastel. Charcoal is also great for bold gestures. A quick watercolour study either as a completed work or as an underpainting to pastels makes for a great exercise. The process gets you doing without over thinking. There is the joyful feeling of bold strokes and swooping brushwork that energises you. No pressure - just good fun.
As so often happens with this approach I enjoy the experience so much that the end result usually ends up framed on my studio wall. It reminds me to loosen up and enjoy the process. It helps not to be attached to the end result too much.
Try this approach when you feel tired or lacking in inspiration from your day job. It is guaranteed to give you more energy and freedom from distractions that deplete you. That is the power of spontaneous creativity.