Original size: 7455 x 4923 pixels (open image in a new tab to see it in 1514×1000 pixels)
The image was painted using “dry media” brushes, mostly pastels and the grainy pencil for details. These brushes have strong grainy characteristics and can produce soft, easily blended colors.
Here is a detail of the image which better shows the grainy texture of the painting:
One important detail regarding the use of these (and other) brushes in high resolutions. There is the “size scale” parameter in the brush support tools which enlarge all brushes including their grain properties! You can change this parameter to quickly change grain size without messing in the brush constructor!