Traditional Yemeni Al-Qasab Gypsum Qamariya Stained Glass Fanlights

Rising like terracotta skyscrapers against the dramatic volcanic peaks of the Yemeni highlands, the multi-story tower houses of Old Sana'a represent one of the most astonishing vernacular architectural achievements on Earth. Constructed from lower courses of dark volcanic basalt and soaring upper stories of sun-dried adobe mud-brick and kiln-fired clay, these 500-year-old structures reach up to nine stories in height. The crowning glory of their vertical facades is the Qamariya—a semicircular or pointed arched fanlight combining brilliant colored glass with lacework gypsum tracery.

The term derives from qamar, the Arabic word for moon. In ancient Southern Arabian architecture, before the widespread availability of imported glass, master builders cleaved thin slabs of translucent native alabaster (marmar) to glaze these high apertures. At night or during high noon, the alabaster filtered harsh desert sunlight into a tranquil, milky lunar luminosity. With the arrival of mouth-blown colored glass via Venetian and Ottoman maritime trade routes in the 16th century, Yemeni artisans fused their ancestral stone carving heritage with vibrant polychrome glazing, creating an architectural masterpiece celebrated on UNESCO's World Heritage list.

The structural matrix of a Qamariya is not wood, lead, or modern concrete; it is hand-cast and hand-carved al-qasab (also termed juss), an exceptionally pure, fast-setting gypsum plaster quarried from the crystalline sediment beds of the Sana'a basin. To manufacture the plaster, raw gypsum rocks are stacked inside artisanal stone kilns and fired with wood and dried dung for 24 hours at temperatures between 150°C and 180°C, driving off three-quarters of the chemically bound crystal water to synthesize calcium sulfate hemihydrate (plaster of Paris).

In the craftsman's workshop, this fine white powder is mixed with pure water into a creamy, high-density slurry and cast into heavy semicircular wooden frame molds resting on flat stone beds. The slab is cast to an extraordinary thickness—typically 40 mm to 60 mm. This monumental depth is critical: it provides the structural rigidity necessary to span window openings up to 1.5 meters wide without secondary iron armature, while providing massive thermal insulation against extreme high-altitude desert diurnal temperature swings.

Once the gypsum slab achieves its initial set—entering a firm, damp, leather-hard state known as 'green' gypsum—the master carver (ustadh) executes the layout using only an iron compass, an ink string, and a straightedge. The patterns are divided into two foundational design categories: shamsiya (solar radiating geometry, characterized by 8-, 12-, or 16-pointed intersecting stars and interlacing geometric strapwork) and kawkab (organic vegetal scrolls, interlocking palmettes, and sacred cypress tree motifs).

With blinding speed before the gypsum crystallizes into rock-hard stone, the carver cuts through the 50 mm slab using an array of curved iron knives (minqash). Aperture by aperture, the negative voids are excavated, leaving behind a delicate web of freestanding gypsum ribs. The craftsman then executes angled beveling, slicing the internal walls of every rib back at a 45-degree angle. This chamfer turns each rib into a light-funneling prism that captures low-angle solar rays and bounces vibrant jewel-toned light deep into interior rooms.

Glazing the Qamariya requires ancestral organic chemistry. Shards of mouth-blown colored glass are scored and snapped to match the unique polygonal shape of each carved cell. To bond the glass to the gypsum frame, the artisan brews a molten mastic composed of wild mountain pine resin (samgh), unbleached beeswax, and fine gypsum powder. Applied boiling-hot to the rear rebates of the tracery, this aromatic resinous mastic sets in minutes, creating an elastic, 100% waterproof seal that absorbs thermal expansion differentials without cracking the delicate glass.

When hoisted into place high within the salon walls (diwans and mafrajs), the Qamariya serves as a sophisticated environmental buffer. High in the mountains at 2,200 meters elevation, solar ultraviolet radiation and daytime heat are intense, while night temperatures drop near freezing. The thick gypsum slab blocks direct thermal conduction, while the high arched position allows warm air to collect near the ceiling and escape through adjacent vents, bathing the living space in radiant emerald, cobalt, amber, and ruby illumination that has enchanted travelers for centuries.