Mosaic gold is also known to alchemists as aurum musivum or aurum mosaicum due to its mottled formation. Forgotten in the data fields of time, mosaic gold is once used by artists for bronzing and gilding, especially wood and metal, beloved for its enchanting shimmer.
What is Mosaic Gold?
Mosaic gold, or bronze powder, is mainly the compound tin(IV) sulfide or stannic sulfide. It appears as a yellow, scaly crystalline powder. Its shimmering quality makes it desirable for bronzing and gilding, especially on wood and metal surfaces.
Mosaic gold is one of the inorganic pigments, along with Prussian Blue, Paris Green and the enigmatic Purple of Cassius. Its luster enhances a colorful spectrum of arts and crafts, where aesthetic richness is harmonized through natural and synthetic pigments.
Historically, the term mosaic gold also describes techniques such as ormolu, from French or moulu (ground or pounded gold). Ormolu is the process of gilding bronze objects with a mixture of high-carat gold and mercury, and also refers to objects finished in a similar manner.
The mercury vaporizes from the object in a kiln, leaving a fine hard gold plating. This same practice appears among the ancient Romans, who brush a substrate with a mix of gold and mercury, then heat the substrate until the invisible mercury vapors drift away, sort of.
For some centuries, mosaic gold maintains a revered status among artisans and alchemists. Alchemists view mosaic gold as a compound with potential. Along with tin purification, pigment making is an alchemical pursuit.
Mosaic gold is also a term used for thin gold sheets cut into squares and used in Byzantine mosaics. In this case it's actual gold, not stannic sulfide.
The Making of Tin(IV) Sulfide & Mosaic Gold
Alchemists prepare tin(IV) sulfide by combining mercury, filed tin, sal ammoniac, and sublimated sulfur (fleur de soufre or flowers of sulfur). The tin can be purified first if needed. According to the experts tin(IV) sulfide is non-toxic but may cause skin irritation. Wear gloves.
These ingredients are ground and mixed together, and set for three hours in a sand bath. The mercury evaporates and vapors are dangerous if inhaled. When the sublimate is taken off, aurum mosaicum is found at the bottom of the matrass.
When heated to 580 °C, the tin(IV) sulfide transforms into this distinct golden yellow pigment sought by artists, a shimmering powder. The pigment is not only valued for its ethereal tone but also for its light interaction, enhancing depth and texture in art and architecture forms.
Mosaic gold is often used during the Renaissance as artists seek to evoke feelings of grandeur and divinity. Famed artist Giotto is known to use mosaic gold to enhance the celestial feel in his work, connecting the divine with the earthly.
Due to toxicity of elements it's not recommended (and probably illegal) to make this pigment. Do not mess with mercury. The pigment influences scientific practices as well, due to its enhancement of light. Early microscopy uses powders such as mosaic gold to enhance visuals.
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