You will need to check any cover slip you plan to use under the polarizing scope to see if it polarizes and, if it does, whether it interferes with the study of crystals or fiber. We found one type of cover slip made of a polymer that appeared to be acetate. These are the very inexpensive type that come with children's microscope kits. These slips produce a lot of polarization and actually enhanced the study of crystals because they produced a changing colored background for the crystals. This activity can be used as a laboratory activity with two to four students in a group or, if a microscope is available that can be adapted to project on a large-screen TV, the activity can be done as a class demonstration.
Crystallization can be slow, especially on humid days.
Indirect heating as mentioned in the procedure can speed crystallization but may produce smaller, irregular crystals. Point out to students that one advantage of viewing crystals under a polarizing scope is that you can readily see irregularities and modify procedures to produce regular crystals. Teachers should verify their own results prior to the use of these lesson plans in a classroom setting. Safety glasses or goggles should be worn at all times. Other protective clothing should be worn as instructed by the teacher.