Charge transfer by fracture between colliding ice particles is measured using a wind tunnel inside a cold room. The charges were recorded one by one and the mechanics of each collision was studied in detail. The sign of the temperature gradient at a given point of impact on the surface influences the sign of the charge transfer. In this work we extend previous measurements to particles growing by riming. A cylinder growing by riming in a wind tunnel was used as target for collisions at 5 m s-1 with ice spheres of 100 μm in diameter in a wide range of temperatures. Charge transfers of either sign were also observed here and according to the ambient conditions, one of sign prevailed on average. The transferences ranged from ¿50 fC at higher temperatures increasing in magnitude to -80 fC at lower temperatures. There was ample evidence of fragmentation following most of the collisions. The influence of the growth regime on the charging and the production of fragments were also studied. A physical model of the microscopical mechanism leading to the charging of the fragments is presented. The laboratory evidence, when applied to a thundercloud, suggests that the proposed mechanism could operate in a wide range of conditions and even explain some observations in situ related to the abundance of ice crystals. Comparisons are made with other experiments and models on static charging of ice. ¿ American Geophysical Union 1994