Co₄Fe₆O₁₆Sb₂

Architectural potential

A cobalt-iron-antimonate ceramic fired at 1100 °C — a structural ceramic with the saturated blue colour that cobalt delivers in oxide form, at one hundred megapascals of compression. Placements are the same structural-brick register as the lithium-iron sibling: block-work in load-bearing walls, extruded posts in garden architecture, structural tile in compressive vaults, and thin-section infill in brick-grid façades where the cobalt blue is the specific architectural argument — a saturated colour that fired ceramic can carry but paint cannot match for permanence. The natural placement is a blue structural wall in a courtyard, a chapel, or a civic entrance, where the mass and the colour do the same work. Embodied CO₂ runs nearly three and a half times that of clay brick, so the chromatic argument has to carry the specification; the material is a signature element, not a bulk block. The low apparent density at 0.54 g/cm³ on a 120×120×130 mm slab points to a substantially porous sintered body, which means the thermal-mass argument is weaker than the lithium-iron variant — this body insulates more than it stores. The 1000 g batch with a five-kilogram ceiling supports a small wall or a courtyard insert. The caveat is toxicity: antimony in the lattice demands careful handling in cutting and drilling, and the €65.13 kilogram-batch price keeps it in signature-element register.

Material character

The body reads a deep saturated blue, the cobalt-antimonate combination sitting more toward ultramarine than toward the greener cobalt-aluminate blues of traditional ceramic glazes — a distinctly mineral, almost lapis-like tone. At 0.54 g/cm³ over 120×120×130 mm the slab is startlingly light for its size, registering a high-porosity sintered body rather than a dense ceramic — closer in hand-feel to a fired aerated concrete block than to a standard structural tile. Surface matte from the sinter, with visible coarse grain in raking light; edges cold-cut, kerf-whitened. Fully opaque. Rings short and muffled under a tap, the specific acoustic of a porous body.