Abstract: The shallower wells of a crystalisation plate in which it is intended to form crystals are part-spherical and of uniform wall thickness. The optical effect of the transparent plastics material from which the plate is moulded counter the distortion of a view through a microscope so that crystals viewed through the microscope appear to be on a flat surface. Associated with the wells are markings so small that they can be read through the microscope, making it unnecessary for the user to take the eye off the microscope to determine the position on the plate.