A few years ago I found a small painting I did in the nineteen seventies. It was the picture of a cloud over a beach. The cloud looked like a block of concrete in the sky, challenging the laws of nature. Ever since I graduated from art school I struggled with the question how to paint clouds. It took quite some time till I found an answer. It is called layering, painting in transparent layers.
The other answer I found is this: when you’re painting clouds, edges are essential for their soft, fuzzy appearance. Almost every cloud has a soft edge, a buffer zone between the blue of the sky and the cloud itself. If you’re smart you’ll work on that at an early stage, when the blue of the sky is still wet.