K₁₂O₁₈W₄

Architectural potential

A thermal-mass ceramic crossed with an electrochromic overlay — the tungstate chemistry gives the body a voltage-switchable tint alongside its slow-heat-release behaviour. This is a rare combination: a wall infill that stores daytime solar gain and also darkens on signal, shifting both the thermal and the visual register of a south-facing façade. Natural placements are trombe-wall cores in energy-retrofit work where the inner face is visible from a circulation gallery and the tint-on-signal register is wanted, double-skin façade infills in offices where morning clarity and afternoon darkening are programmed against the solar path, and atrium-wall panels in civic buildings where the diurnal colour-shift becomes part of the public reading of the space. Compression sits at 100 MPa, so this is a supplement to the structural frame, not a replacement — it infills rather than carries. The CO₂ cost is high, over three times that of a clay brick, so the argument is purely functional: an envelope element that does two things at once, paid for by removing separate mechanical shading and separate radiant-heat storage from the same wall. The caveat is fragile: €50.94 per 200 g puts this at the most expensive tile-cost in the batch, supply-chain score is zero on the tungsten content, and architectural-scale integration of electrochromic tungstate in a thermal-mass body is untested beyond laboratory prototypes.

Material character

The fired body reads a neutral warm off-white with a faint lemon-cream cast from the potassium-tungstate flux — brighter than the praseodymium-bearing rare-earth ceramics and cleaner than the molybdate thermal-mass sibling in this same batch. At 3.75 g/cm³ and 85×85×37 mm the slab handles with solid ceramic heft without crossing into stone-weight, a firm two-finger grip that settles into a confident one-hand carry. Surface finishes vitrified-matte from the 1250 °C fire, the tungstate phase giving a very fine closed grain visible under raking light; edges cold-cut, kerf-whitened along the arris. Under a small DC signal the face shifts toward a pale slate-blue, uniform across the face without patchiness, then clears again when the signal drops.