To make scratches visible, use directional light and adjust angles until the marks catch it.

• Use a hard, small light source rather than very diffuse light.
• Place the light very low to the surface, almost parallel to the glass, so scratches show as contrast.
• Try the light behind and slightly to one side so it doesn’t cast an obvious shadow into the shot.
• Use Live View and slowly tilt the watch and/or move the light until the scratches “light up” or become dark lines.
• Shoot from an angle rather than straight on; reflections often hide defects when viewed head-on.
• If your camera allows it, use manual focus and focus precisely on the scratches, while keeping enough depth of field for the damaged area.

A polarizing filter may also help reduce some reflections. In some cases, cross-polarization (a polarizer on the camera and polarized light source) can make damage on reflective or translucent top layers stand out more clearly.

The key is not expensive gear—it’s controlling reflection by changing the light and viewing angle until the defects become visible.