Ca₂Nb₂O₄₂P₁₂W₂

Architectural potential

A thermal-mass ceramic with an electrochromic tungstate overlay, sibling to the potassium-tungstate variant but built on a calcium-niobium-phosphate backbone. The phosphate content lowers the effective firing window slightly and gives the body a slightly lighter hand-feel, but the dual function — diurnal thermal storage plus voltage-switchable tint — stays intact. Natural placements are double-skin façade infills in offices and schools where the morning-clear, afternoon-darken cycle is programmed against the solar path; trombe-wall inner faces in retrofit apartments where the wall reads from the circulation side; atrium-ceiling panels in civic buildings where the diurnal colour shift becomes part of the public reading of the space; and prototype skylight surrounds that combine radiant-heat capture with passive visual signalling. Compression at 100 MPa keeps the panel in the infill register rather than the structural one. The three-hundred-per-cent CO₂ cost against clay brick forbids any bulk use: the material is bought for the pairing of functions, and the argument is that one element replaces two separate systems. The caveat is the same pattern as its K-W sibling: €35.16 per 200 g batch, supply-chain score near zero on the tungsten content, workshop maximum of 500 g, and untested in architectural production beyond laboratory-scale prototypes. This sits in the same signature-tile register — one element per project, not a repeated envelope surface.

Material character

The fired body reads a neutral pale off-white with a faint cool grey undertone, lighter and cleaner than the potassium-tungstate sibling and closer to a fine porcelain in first reading. At 3.07 g/cm³ and 85×85×45 mm the slab is the thickest in the batch but handles lighter than its size suggests, a two-finger lift that reads closer to a dense fired tile than to a stone. Surface finishes vitrified-matte from the 1250 °C hold with a very fine closed grain; edges cold-cut, kerf-whitened. Under a small DC signal the face shifts to a pale slate-blue that reads more uniformly than in the potassium variant, a cleaner transition.