I will soon have finished another drawing [= watercolor], in the spirit as Den Tessaro [art-seller in Antwerp] wished another one, that is 'airy' and… - Willem Roelofs

I have experienced this country of the great mountains [Switzerland] superb! .. ..[but] I positively believe that nature, most appropriate to be reproduced in painting, is the modest landscape which seems just ordinarily and very insignificant. (translation from original French: Fons Heijnsbroek)

Paint studies of parts, for instance a piece of land, a group of trees or things like that, but always in a way that people can understand these things in relation with the whole landscape, by adding behind that group of trees the air in a right tone color and thereby in connection with the trees.. .Furthermore studies of a whole, preferably very simple subjects - A meadow with horizon and a piece of air to examine further the general tone color, the harmony of the whole.. ..and study nature even more by thinking about it than working after it. (translation from original Dutch: Fons Heijnsbroek)

The drawings [his watercolors] usually succeed in one day or at most two days or they develop difficult and usually don't finish well, then.. ..[I hope] the end will be as good as the beginning. (translation from original Dutch: Fons Heijnsbroek)