The term "writing an icon" is at best a mistranslation, at worst an affectation, as some here have stated. It is perfectly acceptable, and grammatically more correct, to say an icon is painted. The Slavic pisat' can mean either write or paint; the Greek root words graphe and graphia also have this dual meaning, in all forms of Greek language, ancient, intermediate, and modern, including the current vernacular. This duality is even preserved in English: Do we not use the term graphic when we wish to describe something in great detail, as in visual, pictorial terms?
Even the Greek work eikona can mean simply picture, illustration, image, without a religious context; or, in the correct context, means the holy religious art of the Orthodox Church. Similarly, obraz is a Slavic word which has the identical sense as the Greek eikona: that of image. Obraz can refer to any image, and it can refer to an icon. Anyone with a reasonable working knowledge of either Greek, or the various Slavic languages (or both) would be rather bemused at certain English-speakers' insistence that icons are written. It simply doesn't make sense, historically, or linguistically.