The word icon is from the Greek meaning "image". Religious icons of sanctified people or scenes have been used and venerated in the Eastern Christian and Greek Orthodox churches.

The technique, which has changed little over 2,000 years, begins by sticking a preparation of chalk dust and rabbit or fish glue to wood, with flexible lime wood or Canadian pine working best. The picture is then built up layer by layer, beginning with the darkest paints and moving to the lightest, the pigments mixed with egg yolk, a binding process known as egg tempera. When painting on glass, the painting process is reversed, beginning with the light and ending with dark colours.

Dark colours symbolise death and tomb, and light colours represent heaven and resurrection. Icons are flat, two-dimensional, with every aspect - people, landscapes, buildings, animals - depicted as transfixed by the Divine Presence. The lack of depth is deliberate, the aim being to invite the viewer into a spiritual relationship with the story portrayed.

Typical scenes are images of God, Mary, angels, saints and significant feast days such as the nativity or crucifixion. The oldest surviving portable icons are from the early sixth century, and found in St Catherine's Monastery, Sinai. These are painted in encaustic, or wax mixed with pigment. From the ninth century, the egg tempera technique replaced this encaustic method.

Some people see a connection between Coptic iconography and ancient Celtic art. Our most famous illuminated manuscript, The Book of Kells, completed around 800 AD, is full of intricate decoration and interlinear drawings, and in common with icons, its emphasis is on spiritual symbolism rather than realism.

• Mihai Cucu and Zsuzsanna Mara can be contacted in Romania on 0040-740216428, in Ireland on 086-3692037, or mihaicucu78@yahoo.com and zsuzsamara@yahoo.com. A growing interest in iconography in Ireland led to the formation of the Association of Iconographers of Ireland in 1992, e-mail wparchives@oceanfree.net AD