An icon is different from a religious painting. (The latter includes private devotional images like the Sacred Heart of Jesus and Divine Mercy, as well as images of apparitions such as Our Lady of Guadalupe and Our Lady of Fatima.) It is sometimes difficult to articulate the differences, although the “look” of each is immediately apparent.
Icons are the earliest Christian works of art. St. Luke is said to have made the first ones, of Mary the Mother of God. I won’t go into the detailed history, but over the centuries the east and west grew apart in language and expression of worship, although not necessarily in teachings. Once there was a definitive split in the Church, the Roman/Western Church moved toward self-expression and individualism, while the Eastern Church continued to uphold and safeguard the style and traditions of the Holy Icon.
First and foremost, an icon is the liturgical art of the Eastern Orthodox Church. It is an integral part of every form of worship and liturgy. As such, it follows the canon and guidelines of the ancient tradition, as approved by the bishops. The icon is not signed, as it is not about the skill and fame of the artist, but rather for the glory of God. Neither are new and original icons constantly designed: icons instead faithfully translate the original teachings and dogma of Christianity. The aesthetic rules of Byzantine theology and symbolism are applied. It can be said that every icon is an image of Jesus Christ. Every icon is a witness to the Incarnation of God. A physical likeness is not important. (The icon always has a name written upon it.) It is a depiction of a person transfigured by grace–a spiritual portrait rather than a physical one. The figures are very stylized. The icon transcends era and nation, reflecting the timeless truth of a catholic Church for all humanity.
Western Church, art serves more of a decorative purpose than a doctrinal one. An artist is free to interpret the subject matter and to express him/herself in any way that is pleasing–and which the market will accept. There is no imprimateur or particular standard to meet with paintings. The artist’s imagination is free. The works thus naturally reflect the era and culture where they were produced. Attention was paid to likenesses, and the subjects frequently look very realistic, individual and specific.
Western art is very dynamic and active. Figures twist and move. Often they look the viewer directly in the eye, or at the other figures in the composition, in relation to each other. Strong emotions are depicted. There is also expert use of perspective as well as shadows to create a sense of depth, volume, and emotional mood, in the painting.
An icon has a sense of timelessness, stillness, and silence. The mouth is never open; instead the figure listens to the Word of God attentively. Often the ears are large and prominent to emphasize this as well. There is rarely eye contact, more often the figure looks inward/interiorly, or slightly past the viewer. Their gaze is fixed only on the Lord. Figures are lit from the divine gift of grace within, thus no shadows are cast. Backgrounds are flat. As the spiritual is the most important aspect, there is no need to depict depth, weight or volume. Instead, “inverse perspective” is used: rather than a vanishing point in the picture like a set of railroad tracks converging in the distance, the perspective opens up so that the vanishing point ends in the viewer. The figures in the icon move towards the viewer, in relationship with him/her–heaven moving towards the prayerful believer.
This is by no means a comprehensive explanation, nor an absolute one. Icons are distinct from religious paintings, but for a Christian believer, both are beautiful and can speak to the soul, leading one to deeper prayer, and to God.