Method for preparing a silicone elastomer negative mould MN which is of use in the manufacture of moulded articles made of various reproduction materials, comprising the following steps a) to d): a) preparing a polyorganosiloxane composition X which can be crosslinked to produce an elastomer by polycondensation reactions, not containing a metal catalyst and comprising: - a silicone base B comprising at least one α,ω-dihydroxydiorganopolysiloxane oil A, which can be crosslinked by polycondensation reaction, corresponding to formula below: in which formula: • the substituents R 1, which may be identical or different, each represent a saturated or unsaturated, substituted or unsubstituted, aliphatic, cyclanic or aromatic, C 1 to C 13 monovalent hydrocarbon radical and preferably R 1 is a methyl; and • n has a value sufficient to confer on the polyorganosiloxane of formula a dynamic viscosity at 25°C ranging from 10 to 1 000 000 mPa.s, and - a catalytically effective amount of at least one polycondensation catalyst C, b) applying said polyorganosiloxane composition X to a master to be duplicated, optionally covered beforehand with a mould-release agent, c) allowing said polyorganosiloxane composition X to crosslink in the presence of moisture provided by ambient air or by prior addition of water, so as to form a silicone elastomer negative mould MN which is an imprint corresponding to the outer contour of the master to be duplicated, and d) separating the silicone elastomer negative mould MN from the master to be duplicated, characterized in that, during step a), the polycondensation catalyst C is an organic compound corresponding to general formula: (R") 2 NH in which the symbols R", which may be identical or different, represent aliphatic hydrocarbon radicals containing from 6 to 10 carbon atoms. a) preparing a polyorganosiloxane composition X which can be crosslinked to produce an elastomer by polycondensation reactions, not containing a metal catalyst and comprising: - a silicone base B comprising at least one α,ω-dihydroxydiorganopolysiloxane oil A, which can be crosslinked by polycondensation reaction, corresponding to formula below: in which formula: • the substituents R 1, which may be identical or different, each represent a saturated or unsaturated, substituted or unsubstituted, aliphatic, cyclanic or aromatic, C 1 to C 13 monovalent hydrocarbon radical and preferably R 1 is a methyl; and • n has a value sufficient to confer on the polyorganosiloxane of formula a dynamic viscosity at 25°C ranging from 10 to 1 000 000 mPa.s, and - a catalytically effective amount of at least one polycondensation catalyst C, - a silicone base B comprising at least one α,ω-dihydroxydiorganopolysiloxane oil A, which can be crosslinked by polycondensation reaction, corresponding to formula below: in which formula: • the substituents R 1, which may be identical or different, each represent a saturated or unsaturated, substituted or unsubstituted, aliphatic, cyclanic or aromatic, C 1 to C 13 monovalent hydrocarbon radical and preferably R 1 is a methyl; and • n has a value sufficient to confer on the polyorganosiloxane of formula a dynamic viscosity at 25°C ranging from 10 to 1 000 000 mPa.s, and • the substituents R 1, which may be identical or different, each represent a saturated or unsaturated, substituted or unsubstituted, aliphatic, cyclanic or aromatic, C 1 to C 13 monovalent hydrocarbon radical and preferably R 1 is a methyl; and • n has a value sufficient to confer on the polyorganosiloxane of formula a dynamic viscosity at 25°C ranging from 10 to 1 000 000 mPa.s, and - a catalytically effective amount of at least one polycondensation catalyst C, b) applying said polyorganosiloxane composition X to a master to be duplicated, optionally covered beforehand with a mould-release agent, c) allowing said polyorganosiloxane composition X to crosslink in the presence of moisture provided by ambient air or by prior addition of water, so as to form a silicone elastomer negative mould MN which is an imprint corresponding to the outer contour of the master to be duplicated, and d) separating the silicone elastomer negative mould MN from the master to be duplicated, characterized in that, during step a), the polycondensation catalyst C is an organic compound corresponding to general formula: (R") 2 NH in which the symbols R", which may be identical or different, represent aliphatic hydrocarbon radicals containing from 6 to 10 carbon atoms. characterized in that, during step a), the polycondensation catalyst C is an organic compound corresponding to general formula: (R") 2 NH in which the symbols R", which may be identical or different, represent aliphatic hydrocarbon radicals containing from 6 to 10 carbon atoms.