Kalenderblad februari met staande en zwemmende eend 1908

Theo van Hoytema made this calendar page for February with standing and swimming duck, but what medium did he use? It looks like it could be made with lithography. I think this artwork is lovely and shows a calm scene of two ducks in the water. One is swimming and has a yellow beak, and the other is standing behind it looking slightly darker. I find it impressive when an artist can capture the movement of the water and the stillness of nature. It must have been very peaceful watching the ducks. I can see the artist has used different techniques here such as blending the colors to create an interesting visual texture. I wonder whether Van Hoytema has made similar prints of calendar pages, or other natural scenes. I am in awe of the artistic process and how artists inspire one another across different periods.