Unfortunately little fluffy clouds are very popular on the ceilings and walls of children’s rooms, so if you look on the internet, you will find many sites telling you how to make repetitive, fluffy clouds. However, there are also some advice sites for watercolor clouds which suggest using pretty much the same gimmick.
In the general class of watercolor techniques sometimes called “letting the watercolor paint itself”, it is suggested that you make a sky wash and then use cotton balls to dab here and there removing some of the wash to make cloud forms. Then you might perhaps dab in a little dark shadows as well (by first dabbing the cotton into paint). To see an example of this advice see here.
This produces, not surprisingly, cottony cumulus cloud forms or, if you pull the cotton ball apart first, wispy cirrus forms. Done right it does suggest forms that you could fly through.
The first problem with this method is that it looks like you’ve used cotton balls. It falls in the same category as using a sponge dipped in paint for foliage. Officially I think the way to describe the problem is that “the finish” is too mechanical. They do not have the painter’s signature style. Bob Ross made a career out of this approach, showing people gimmicks for just about everything you can imagine. To be fair there is always a tension between using some shorthand calligraphy to depict something quickly and really taking a detailed look and making a more accurate representation.
The second problem is that clouds made this way are not interesting or particularly realistic. Usually there is no perspective, and the clouds do not look particularly dramatic. They are not complex, intricate, rough, etc. If you use this method, your sky will probably be of the back curtain type.
Clouds are not an afterthought in a landscape, particularly with a low horizon. Clouds are not “cute”. They are awesome (“sublime” or “picturesque”) when you actually think about them or you are in an airplane that flies around a huge cumulo-nimbus thunderstorm. In fact. the term “sublime” which derives from “looking up” seems to have referred originally to the sky, the “empyreal” realm.
A more convincing approach is to use a crushed paper towel, preferably of the cheap, rough variety pressed against a still wet blue sky wash. You can press and roll such a towel for pretty good results. If you press very hard, you get a very white cloud, and, if you press less hard, you’ll get a cloud with some blue shadow in it.
I think this approach is useful if you don’t intend the sky to particularly prominent in the painting. Nor is the sky particularly dramatic using these techniques.
