Different methods for the impregnation of wet archaeological leather were compared. These methods were compared with new ones, involving impregnation with water-soluble silicon monomers mixed with a plasticizer, followed by in situ polymerization. The best results were clearly obtained through impregnation with PEG 400 and with a mixture of polyviol and glycerine. We preferred the former for its lower hygroscopicity. This methodology was applied to a shoe from the 13th century. The shoe was impregnated for seven weeks in 50% PEG 400, freeze-dried for 24 hours and conditioned at 55% relative humidity and 21°C for several weeks: the water-uptake was 18% of its weight after lyophilization. The leather was supple and its color turned from black, before treatment, to deep brown. Impregnation with silicone monomers might be fruitful for the treatment of very deteriorated leather: a plasticizer must be added to introduce enough suppleness into the tri-dimensional silicon polymer.