Cu₂K₄S₃₂

Architectural potential

At 50 MPa this is the lightweight, low-compression end of the cold-cast sulfide family, which re-casts it in architecture as a surface-and-cladding material rather than a structural one. The softwood-scale density and the zero-kiln chemistry mean full wall-area coverage becomes possible without load penalty to the substrate behind it: tall gallery walls, ceiling-plane inlays, acoustic-absorber panels in lobbies and auditoria, and decorative-cladding tiles in exhibition architecture are the natural placements. The copper-potassium polysulfide surface bloom is denser and more crystalline here than in its sodium cousin, so the face reads as a more active light-response surface — a slab whose visible texture varies with raking light and time of day. The eighty-nine-per-cent cut in embodied CO₂ against Portland cement applies even at tile scale, so specifying this material in place of a traditional cement-based tile delivers a real environmental argument. The caveat is the low compressive strength: at 50 MPa the slab will not carry any structural load and needs a rigid substrate behind it, so this is a surface specification rather than a block one.

Material character

The slab lifts startlingly light for its size — the eye expects cement-block weight and the hand encounters something closer to kiln-dried pine. At 2.17 g/cm³ this is the lowest density in the cold-cast sulfide palette, a clear step down from the sodium cousin and a deliberate tectonic signal. The green-red copper shimmer is warmer in daylight than the Na-based equivalent because the potassium cation stabilises a marginally longer sulphur chain, shifting matrix absorption slightly toward yellow. The α→β sulfur bloom has deposited a more visible crystalline stipple across the face than in the Na version. Surface mold-matte with meniscus; edges sharp as-cast. Sulphide odour legible under saw-cut.