Celtic knot art splits into four canonical phases. La Tène (c. 500 BC – AD 50) is the Iron Age phase: curvilinear vegetal scrolls, stylised palmette and lotus shapes adapted from Greek Mediterranean prototypes, applied to bronze torcs, mirror-backs, scabbards, the Battersea shield, the Snettisham Hoard, and the Petrie Crown. Insular (c. AD 600 – 900) is the early-Christian Irish and British phase: the great manuscripts (Book of Kells, Lindisfarne Gospels, Book of Durrow), the metalwork of the Ardagh chalice and the Tara brooch, the Pictish symbol stones. Insular is where the true unbroken interlace knot patterns appear, often combined with zoomorphic borders (interlaced birds, hounds, serpents). High-cross stonework (c. AD 750 – 1000) is the open-air phase: Muiredach’s Cross at Monasterboice, the Cross of the Scriptures at Clonmacnoise, the Iona crosses. Stone interlace becomes monumental, paired with figural panels of biblical scenes. Revival (c. 1880 – 1930) is the Arts and Crafts return: John Duncan, Mary Watts at Watts Mortuary Chapel, Archibald Knox’s Cymric and Tudric ranges for Liberty of London, used in book design, jewellery, gravestones, and architectural ornament.
For image generation, anchor each Celtic knot prompt to a specific phase, a specific medium, and a specific use. La Tène: bronze torc, Iron Age rider mirror-back, Snettisham hoard, curvilinear scrollwork, no humans. Insular: vellum manuscript page, gold leaf, lapis blue, vermillion, zoomorphic border, capital letter at the top of a Gospel page. High-cross: weathered grey limestone, Irish landscape behind, monumental scale, rope-and-stepped frame around the figural panel. Revival: Arts and Crafts book cover, Liberty silver, gravestone, Mary Watts terracotta plaque. Mention the period, the medium, and the use directly in the prompt.
Lean into the medium-native palettes. La Tène: bronze patina green, gold underneath the verdigris, dark soil on excavated finds. Insular: deep ultramarine, vermillion, ochre, white-of-vellum ground, gold leaf catching light, the four canonical scribal pigments. High-cross: weathered limestone grey, lichen yellow-green, peat brown of an Irish hill, evening sun raking the carved surface. Revival: muted Arts and Crafts greens, dusty pinks, hammered silver, ivory cream paper. Name the palette in the prompt. The closer you describe what kind of object you are imagining, the closer the result lands to a real artefact.