A model of an air cooler (telescopic cold bridge) with a column of Tamman test tubes (telescopic test comb), installed in a laboratory tube furnace, for regulation and simultaneous crystallization tests at different temperature gradients and crystallization rate intervals, with the purpose of obtaining crystals, is presented. This method can also be applied in crucible and chamber furnaces. (C) 2004 Elsevier B.V. All rights reserved.