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The slight tension in the jaw or the sparkle in the eyes.
Posing was often assisted by hidden metal braces to help the subject stay perfectly still.
Use a single, soft light source from the side. This mimics the window light common in 19th-century studios, highlighting the contours of the face.
Focus on high collars, heavy textures, and matte fabrics. Avoid anything shiny or synthetic, as it will break the historical illusion. Expression