Second-group classification is not defined by hardness alone. It describes materials whose surface behaviour requires closer control because it may be sensitive, reactive, unstable or difficult to predict. The materials below do not share one universal LUXI polishing process: identify the material and surface condition first, then use only a specialist branch that matches the case.

Platinum

Platinum has its own accepted LUXI routes, selected according to sanding preparation and the required control of the surface. Continue with Independent LUXI polishing routes for platinum.

Palladium and palladium white gold

Palladium and palladium white gold require material-specific assessment. This overview does not invent or prescribe a palladium compound-and-wheel sequence. Confirm the alloy and preparation before establishing a route.

Stainless steel and Co–Cr

Stainless steel and Co–Cr belong to a specialist hard-material branch. Continue with Controlled LUXI routes for stainless steel and Co–Cr; use Stainless steel — first polishing stage when that narrower first-stage context is required.

Titanium

Titanium follows a separate temperature-controlled branch. Continue with Titanium finish: standard LUXI Pink or low-temperature LUXI Green.

Other difficult or reactive second-group cases

Zamak, pewter and other zinc or tin alloys belong to this broader behaviour-based family even though not every listed material is physically hard. For their accepted specialist continuation, use Zamak and pewter polishing: LUXI Brown → LUXI Pink.

Unusual hard or reactive alloys, and powder-metallurgy or metal-3D cases whose surface behaviour is difficult or unpredictable, require case-specific assessment. Where the identified hard surface needs the accepted controlled aggressive readiness step, continue with Hard second-group materials aggressive preparation: LUXI Black + Sisal. That specialist branch is not a universal process for every material in this overview.

These branches are related by polishing behaviour and material classification, not by hardness alone and not by one mandatory or interchangeable process.