A novel mercury seal technique has been developed that facilitates the processing of the solutions with immersed seed. This technique enables a seed crystal to be introduced into the crystallizer prior to the processing of the solution, and hence allows the seed to be present in the growth chamber during filtration and overheating operations, while at the same time preventing the seed from being dissolved by the under-saturated solution. When the solution processing is complete and the solution has been cooled to near-saturation temperature, the mercury seal is removed, exposing the seed to the Solution thereby allowing the growth to start. Usefulness of this technique has been demonstrated by growing crystals of DKDP and KAP in 5-1 crystallizers without any extra nucleation. (c) 2005 Elsevier B.V. All rights reserved.