Soft-Focus Effect

A fine line is visible mostly because of its shadow. A crease is a groove, a groove holds a shadow, and the eye reads the contrast between the lit edge and the dark bottom as a line. Take the contrast away and the line stops announcing itself, though the groove is where it was.

That is what an overcast sky does, and a large diffuser in front of a lamp: light arrives from many directions at once, so nothing casts a hard edge. A soft-focus formula reproduces that on a small scale. Particles that throw light sideways — fine spheres, thin platelets, some pigments — turn one hard source into a spread of small ones sitting just above the surface.

The same scattering blunts differences in colour. A red mark or a brown one shows up by contrast with what surrounds it, and light bouncing between the skin and the particles above it mixes the edges together. Nothing has been lightened. It has been smeared, in the useful sense.

All of which is worth holding in mind at the shelf. Blurs the look of pores is a description of an optical effect, and one of the few cosmetic claims that can be demonstrated honestly in a photograph taken a minute after application — which is also why such photographs are easy to produce. It washes off with the product, the wrong light undoes it, and it says nothing about next month.