How does transparent enamel reveal engraving beneath it?

Transparent enamel reveals engraving beneath it primarily through its ability to allow light to pass through the vitreous layer. When applied over a metal surface—typically gold or silver—that has been engraved or carved in low relief, the translucent enamel acts as a medium that catches and reflects light off the underlying metal.123

In techniques such as basse-taille, the enamel is applied in varying thicknesses over the modeled surfaces of the engraving. Because the enamel is level on its outer surface, the depth of the engraving creates subtle variations in the thickness of the enamel layer. As light penetrates the translucent material and reflects back from the metal base, these thickness variations produce different tonal strengths. This interaction between light, the reflective metal, and the colored enamel creates an impression of plasticity and three-dimensional depth, effectively making the engraved design visible through the enamel coating.21