Process for making an object from plastic material, comprising the following operations: - moulding at least one insert by injecting a first plastic material into a first moulding cast, said first cast being configured so that said at least one insert comprises a base from which exposure reliefs extend, such exposure reliefs being intended to be visible when the object made of plastic material is finished, between said exposure reliefs passage channels being defined for a second plastic material in a subsequent overmoulding operation, - positioning said at least one insert in a second moulding cast, so that said insert is positioned with said base pressed against a first surface of a first half-mould of said second cast, and with said exposure reliefs pressed against an opposite second surface of a second half-mould, - overmoulding a second plastic material on a part of said insert, by injecting said second plastic material into said second cast, so that said second plastic material injected fills said second cast passing through said passage channels defined between said exposure reliefs of said insert, covering said base and being interposed between said exposure reliefs, characterised in that - at least one of said exposure reliefs has a hollow surrounded by a perimeter sealing edge configured to prevent the entry of said second plastic material into said hollow during said subsequent overmoulding operation, - said insert is positioned with said base pressed against said first surface of a first half-mould of said second cast, and with said sealing edge pressed against said opposite second surface of said second half-mould, so that said second plastic material injected fills said second cast passing through said passage channels defined between said exposure reliefs of said insert, and without entering into said hollow of said at least one exposure relief. - moulding at least one insert by injecting a first plastic material into a first moulding cast, said first cast being configured so that said at least one insert comprises a base from which exposure reliefs extend, such exposure reliefs being intended to be visible when the object made of plastic material is finished, between said exposure reliefs passage channels being defined for a second plastic material in a subsequent overmoulding operation, - positioning said at least one insert in a second moulding cast, so that said insert is positioned with said base pressed against a first surface of a first half-mould of said second cast, and with said exposure reliefs pressed against an opposite second surface of a second half-mould, - overmoulding a second plastic material on a part of said insert, by injecting said second plastic material into said second cast, so that said second plastic material injected fills said second cast passing through said passage channels defined between said exposure reliefs of said insert, covering said base and being interposed between said exposure reliefs, - at least one of said exposure reliefs has a hollow surrounded by a perimeter sealing edge configured to prevent the entry of said second plastic material into said hollow during said subsequent overmoulding operation, - said insert is positioned with said base pressed against said first surface of a first half-mould of said second cast, and with said sealing edge pressed against said opposite second surface of said second half-mould, so that said second plastic material injected fills said second cast passing through said passage channels defined between said exposure reliefs of said insert, and without entering into said hollow of said at least one exposure relief.