Is pigment surface treatment mandatory in a silicone system?

Not by rule, but in a silicone system carrying a water-resistance or long-wear claim it is close to unavoidable.

The treated grades on our list carry the same pigment with different layers: SI for slip, water resistance and dispersion in silicone; AS for dispersion in oils and silicones with lower oil absorption and more loading headroom.

Where it is effectively required: silicone-containing formulas claiming water resistance or wear; high pigment loads such as liquid foundations and slurries; systems whose viscosity is sensitive to oil absorption; and anything needing long-term stability.

Where it can be skipped: pressed powders and eyeshadows with low oil content, and cost-driven filler formulas where the treated premium buys nothing.

Remember that changing the treatment changes the formula. Re-test dispersion, viscosity, stability and shade — the layer alters optical behaviour, and pale and bright shades show it first.