Immediately and definitively [after starting a painting] I determine the effect of sunlight, day and shadow, without being concerned with any detail.… - Barend Cornelis Koekkoek

..on the banks of a very picturesque mountain stream that pours out its crystalline water in four or five waterfalls into the Dussel brook.. .Oh, in this cave, at this crystal flood, I often felt myself so well! Sensations frequently welled up in my bosom at this blessed place that ennoble the soul and make pour out joyful tombs; [they] give the heart impressions that neither greatness or honor can steal from us. An indomitable longing came to me, to learn more and more about these enchanting shades of beautiful and holy nature, and to transfer them on the canvas with my brush.

The pursuit of perfection in art must always be a noble duty to the artist, but.. .Here [at the Drachenfels ] he feels, more than in any other place, too vividly his inability.. .Stop it, painter! Just please yourself with the impression it makes on your soul; try, if you can, to keep this impression pure, it will teach you how to create ...

(original Dutch, citaat van B.C. Koekkoek:) [de natuur] alleen schenkt u die bij eene aandachtige beschouwing harer majesteit en grootheid.. .Spreidt zij geene prachttaferelen voor uw oog ten toon, die onmogelijk een ander u zou kunnen beschrijven?. ..die gij naderhand op uwe kamer op het doek of paneel kunt trachten te verwezenlijken.