K₁₂Na₄O₁₆Si₄

Architectural potential

A high-potassium alkali-silicate glass sitting squarely in the load-bearing transparent-glass register — 500 MPa of compression at 2.57 g/cm³, fully clear, and firing at 1150 °C against float glass's standard palette. Natural placements are pressed-glass stair treads walked on from above, transparent floor panels over light-wells in retail and exhibition interiors, column-like light-admitting piers in atria and circulation cores, partition glazing that carries its own vertical load, and monolithic glass balustrades where the structural glass replaces the usual steel-plus-glazing assembly. The K:Na ratio pushes alkali content unusually high, so the glass accepts slower annealing and thicker pressings than standard soda-lime sheet — the tectonic register is pressed and cast glass rather than drawn sheet. Against float glass the CO₂ is essentially identical (minus two per cent) but the energy cost runs sixty-two per cent lower, which is the real argument: a structural glass at architectural scale with significantly less kiln time per kilogram. The caveat is chemical durability: high-alkali glasses are more susceptible to surface leaching and weathering than soda-lime, so exterior exposure requires either laminated skins or a lime-silicate glaze, keeping specification interior-biased unless the element is protected.

Material character

Clear with a faint warm potassium cast — the pressed 85×85×54 mm slab reads nearly water-white under daylight, with the depth of the 54 mm section giving a just-perceptible amber along the long edge. At 2.57 g/cm³ the piece is firm-handed but not heavy, a distinct weight step below the borosilicate and lead-bearing glasses. Top face carries a pressed-glass anneal texture with fine striae visible along one axis; edges come cold-cut with the lapidary dust left on the kerf. Against standard float glass the body reads a touch warmer and softer, and the pressed tectonic gives a top-face crown that conventional rolled sheet does not carry.