A design for a modular air cooler ("crystallization shelf"), installed in a laboratory tube furnace is presented. The setup allows easy regulation and simultaneous crystallization tests of a series of different temperature gradients, shapes of crystallization fronts and rate intervals in crucible columns, with the purpose of obtaining crystals. This method can also be applied in crucible or chamber furnaces. (c) 2005 Elsevier B.V. All rights reserved.