Mix the powder in and cover with a cover slip. Inspect as before. Many of the talc particles will probably be too large to show the effect, but there should be some particles fine enough to show the random motion. In the talcum powder I tried the fine particles were very small, less than 1 m and showed the motion nicely. The older microscopy books describe the use of finely ground gamboge suspended in water to study the motion.
Gamboge is a yellow gum-resin used as a paint pigment.
The motion is also observed in living organisms e.g. the cellular contents of filamentous aquatic algae, or as early microscopists observed - the particles suspended in the medium within living pollen grains. It's probably best to become familiar with the motion first in non-living material in order to more easily distinguish the motion from e.g. the movement of bacteria or cellular activity. He was studying the fertilisation process in the plant Clarkia pulchella when he noticed the motion in tiny particles suspended within the medium of living pollen grains. He went on to show that the motion occurred in non-living as well as living material. Some texbooks, even to university level, incorrectly state that he observed the movement of the pollen grains themselves.