“Hartgen’s aquarelles deploy semi-abstract means to show us nature on flux: the fracture of a wave, snow spume in pines, the rattle of icy branches, winds swooping along forest solitudes. All is changing, nothing is fixed, even in a moonlit silence the mood is one of unseen forces at work. Hartgen is inspired by Chinese masters, yet his symbols of the condition of nature do not accent the unchanging, peaceful inner essence, but rather the immense and chaotic strength of a nature that is constantly destroyed and constantly renewed. His work is colorful and lyric and…is evidence of a rare talent.”
~Robert Taylor, Boston Sunday Herald, 1973