PURPOSE: To provide silicone wafers or a resist ink for etching ISO substrate free from problems of inhibitory impurities to wafers in etching silicone wafers or ISO substrates by uniformly coating the surface of a filler such as talc to be used in resist ink for etching with a coupling agent having extremely low concentration of inhibitory impurities to wafers.

CONSTITUTION: A silicone coupling agent or titanate coupling agent is dissolved in a proper solvent and the surface of a filler such as talc is uniformly coated with the solution to give the filler free from influence of inhibitory components (Na+, K+, Mg2+, etc.) on silicone wafers or ISO substrates and the filler is used to give resist ink for etching silicone wafers or ISO substrates free from problems.