Lava

The figure is a crust with something molten inside it. Light escapes through the cracks, so the body is a container for heat rather than a shape with heat painted on.

It reads as barely held together. Every fissure is a place the surface has already failed, which gives a still figure a sense of pressure.

The source is inside. Light comes out of the cracks and falls on whatever is near, so the ground under the figure picks up orange and the surrounding air does not.

The crust is dark and matte. Cooled basalt is close to black, and the contrast between that near black and the molten orange is what makes the glow read as temperature rather than colour.

Heat shimmer rises above the hottest areas. It distorts whatever is behind it in a slow vertical wobble, which is a cue the eye reads as heat before it reads anything else.

Use it on a single figure against a dark surround, for a reveal or a transformation. It needs darkness around it to work.

Skip it in a bright scene. Daylight flattens the internal glow, and the figure becomes a person in dark textured makeup.

Underlighting is a lamp placed below the subject, outside the body, throwing shadows upward across the face. The light source is in the room.

The check is where the light starts. Light escaping through cracks in the surface means Lava. Light arriving from below and landing on the surface means Underlighting.

The model lights the figure from outside with orange, which looks painted on, as the entry warns. Say the molten light glows through the fissures from within, and name the dark crust between them.

The other failure is a bright surround. Ban a bright background and ask for a dark environment, so the escaping light has somewhere to fall and something to contrast against.