Making Naples Yellow (Lead Antimonate) — The Oldest Known Synthetic Yellow Pigment

MANDATORY SAFETY: This process involves lead (cumulative neurotoxin), antimony (toxic to lungs and gut), sulfur dioxide fumes (from roasting stibnite), and kiln temperatures of 900-1000°C. Equip yourself with a P100/FFP3 respirator with acid gas cartridges, chemical splash goggles, and chemical-resistant gloves. For kiln work, add leather gauntlet gloves over the chemical gloves. ALL stibnite roasting must be done OUTDOORS or under a fume hood — sulfur dioxide is a toxic, choking gas. Keep all lead and antimony compounds WET when grinding to suppress dust. Have clean water, damp cloths, and a fire extinguisher ready.

OUTDOORS ONLY. Crush 100 g of stibnite ore (antimony sulfide, Sb₂S₃) to coarse powder in a mortar. Place the crushed stibnite in a shallow refractory dish or clay crucible and heat over a strong fire or in a kiln at 500-600°C. The stibnite decomposes: the sulfur burns off as sulfur dioxide gas (the familiar choking smell of burning matches) and the antimony oxidises to antimony trioxide (Sb₂O₃), a white to pale grey powder. Keep upwind of the fumes. Continue heating until no more sulfurous fumes are released and the residue is a uniform white-grey powder. Cool completely.

Place 150 g of lead in a refractory crucible and heat to approximately 500°C in a well-ventilated area. As the lead melts (melting point 327°C) and is exposed to air, it oxidises at the surface, forming a yellow-orange powder — litharge (lead monoxide, PbO). Stir the molten lead with a steel rod to expose fresh surface to air. Continue heating and stirring until the lead is fully converted to a fine yellow-orange powder. This may take 30-60 minutes. Cool completely and grind to uniform powder. Wear respirator at all times — lead oxide dust is extremely toxic.

Weigh out approximately 2 parts litharge (PbO) to 1 part antimony trioxide (Sb₂O₃) by weight — a ratio of roughly 100 g litharge to 50 g antimony trioxide. Mix thoroughly in a mortar, adding the materials WET to suppress dust. Transfer the mixed powder to a clean refractory crucible and place in a kiln. Fire at 900-1000°C for 2-3 hours. At this temperature, the lead oxide and antimony trioxide react to form lead antimonate (Pb₂Sb₂O₇), adopting the characteristic pyrochlore crystal structure. The colour develops during firing — lower temperatures (900°C) produce a paler, more lemon yellow; higher temperatures (up to 1050°C) produce a deeper, warmer golden yellow.

Let the crucible cool completely in the kiln (do not quench). The fired product should be a dense, hard, yellow mass or sintered cake. Break it out of the crucible and crush coarsely in a mortar, then wash with several changes of clean water to remove any soluble residues. Grind WET on a glass muller until smooth — the finished pigment should be a soft, warm, opaque yellow powder. Store in sealed glass jars, clearly labelled as toxic (contains lead and antimony). Naples yellow is highly stable, lightfast, and safe in lime (making it excellent for fresco). It has superb opacity and produces a uniquely soft, warm yellow that was a favourite of painters from Giotto through Tiepolo. Handle with gloves at all times.