Shivalik Gypsum and Marble Dust Embossed Relief Gesso: Substrate Chemistry

While the glittering mirror glass of a Sheesh Mahal inevitably captures the spectator's eye, the true structural foundation of Thikri craft is its remarkable relief plaster ground, known in historic guild manuals as gaj-ka-kaam. The substrate had to satisfy contradictory physical requirements: it needed to be pliable and slow-setting enough to permit hours of freehand sculpting, yet firm enough to hold razor-sharp raised relief ribs without slumping; it had to bond tenaciously to smooth glass surfaces, yet possess enough internal elasticity to absorb thermal movement without cracking.

Craftsmen achieved this performance through a sophisticated chemical marriage of two mineral binders: slaked fat lime and calcined gypsum. The lime was derived from pure calcium carbonate limestone, burned in wood-fired kilns and slaked in subterranean water pits for a minimum of six months to two years to eliminate all unslaked magnesium and calcium oxides. To this colloidal lime putty was added calcined gypsum mined from the sedimentary deposits of the Shivalik foothills. While the gypsum provided rapid initial dimensional stability and zero shrinkage during setting, the lime initiated long-term carbonation, absorbing carbon dioxide from the atmosphere over decades to transform the plaster back into crystalline limestone rock.

To convert this binder paste into a sculptural gesso, artisans blended in Makrana marble dust (sang-e-marmar ka boora). Quarried from the famed white marble veins of Makrana in central Rajasthan—the same geological source used for the Taj Mahal—this marble consists of over 98% pure, crystalline calcite. Stonecutters gathered the fine flour generated by hand-sawing marble slabs, passing it through multi-stage water sedimentation tanks to separate particles into uniform micro-grades.

When kneaded into the lime-gypsum binder, the sub-micron marble particles fill all interstitial voids between lime platelets, creating an extraordinarily dense, non-porous paste. The pristine white translucency of the Makrana marble flour gives the gesso its glowing, alabaster-like brilliance. More importantly, the hard calcite crystals allow the finished relief ribs to be polished with smooth agate and jade burnishing stones, developing a silky, glass-hard protective skin that repels dust and moisture without requiring modern varnishes.

The workability of historic Thikri gesso relied on an ingenious pharmacopeia of natural organic admixtures. In the arid, blistering heat of Rajasthan, ordinary plaster loses its moisture within minutes through evaporation, resulting in rapid dehydration, crumbling, and loss of structural bond. To counteract this, master craftsmen mixed the dry powders with herbal decoctions brewed in copper cauldrons.

Chief among these additives was gur (unrefined sugarcane jaggery) and fenugreek seeds (methi). Sucrose acts as a powerful setting retarder: sugar molecules adsorb onto the surface of hydrating calcium sulfate crystals, temporarily poisoning active crystal growth sites and extending the open sculpting time by up to four hours. Simultaneously, gum arabic (the natural sap exuded by the native babul tree, Acacia nilotica) and curdled milk whey (casein) were introduced. These natural biopolymers acted as powerful water-reducing plasticizers and natural glues, dramatically increasing the tensile adhesion between the hydrophilic lime matrix and the smooth, non-porous glass tesserae.

The physical execution of the relief was performed entirely freehand by master stucco carvers (gajdhar). After tracing the design onto the wall using charcoal pounce bags, the artisan loaded a small lump of gesso paste onto a boxwood spatula or flexible horn palette knife. With swift, assured strokes, the craftsman drew raised ribbons of plaster along the charcoal guidelines, building up high-relief ribs (kangura) that projected 5 to 20 millimeters from the wall face.

Crucially, the craftsman cut a continuous 45-degree chamfer along the inner edge of each raised rib, creating an undercut bed or recessed bezel specifically proportioned to receive the cut mirror tessera. While the gesso remained pliable, the cut glass shard was pressed firmly into its bed. The soft plaster displaced around the glass, rising up slightly over the front rim to create a protective mechanical lip that permanently locked the mirror in place without relying on chemical adhesives. Once cured, the exposed stucco ribs were burnished with smooth agate stones, creating a gleaming white jewel-box frame around every faceted glass shard.