Na₄O₂₂Si₈W₂

Architectural potential

A tungstate-doped alkali-silicate glass with electrochromic behaviour: a small DC signal shifts transmission from clear to tinted blue, opening dimmable glazing and responsive partitions without mechanical shading. Five hundred megapascals of compression and a fully transparent body at 3.61 g/cm³ lift this into the load-bearing-glass register, so the element carries structure and daylight in one piece while also carrying a switching behaviour. Natural placements are transparent partitions in office meeting-rooms that tint on command, light-admitting stair treads with switchable privacy zones in mixed-use buildings, south-facing glazed piers in gallery architecture that dim under afternoon sun, and conference-room façade panels where solar gain and visual privacy both need passive-to-responsive control. Against float glass the embodied CO₂ is only two per cent higher while the firing energy drops sixty-two per cent, so the carbon argument is essentially neutral and the energy argument is clean. The supply-chain score sits at 1.0 and confidence is high, so specification is unusually robust for a switching glass. The caveat is cost: at 72 euros per 400 g workshop batch this is a signature glazing element rather than a bulk façade material, and the electrochromic drive wiring adds a real control-integration layer to the tectonic.

Material character

A clear alkali-silicate glass at 3.61 g/cm³ in an 85×85×38 mm slab — noticeably denser than standard soda-lime float glass of the same dimensions, so the slab sits with an unexpected heft when lifted. The body reads fully transparent at rest, with the tungstate trace giving a faint warm undertone in thick section. Surface carries pressed-glass register: a low convex crown from the annealing cycle, two thin anneal striae near the long edges, and cold-cut sides with lapidary bloom. Switched, the body shifts to a uniform dusty blue tint without losing geometric clarity. Against a simple soda-lime sibling the weight step and the switching chromism together separate this decisively from architectural float glass.