Complex precipitation structures: a Fingers with a precipitation disc, concentration of oxalate 0.05 M. On the left upper corner the pellet is visible (20 min after beginning of experiments). B Top view of a precipitation disk (CuC2O4 ) with crystals on top, oxalate concentration 0.11 M 24 h. C Side view of this structure. The formation of the disk occurs in 20 min. The disk diameter is about 3.0 cm. The picture was taken after 24 h.