This study is aimed at challenge to rational design of precipitation reaction by complexation between ligands and metal ions to give crystals of the complex having various types of shapes and sizes.  Participants are encouraged to propose suitable ligands, precursors for ligands, pH buffers, source of bases, and reaction conditions.  By careful observation of precipitates and crystals obtained by the proposed complexation-precipitation reactions, factors determining the crystal shape and size will be discussed.  Experience the wonder of microworld of crystal formation.