• Common household chemicals: this includes Iodine, for example. They are very readily available.
• Substances used mostly for microscopy: Methylene blue, Hematoxyline, and Eosine belong to this group.
• Commercial substances: they are sold by companies specializing in microscopic chemicals.

The article also provides a step-by-step guide on how to stain a blood sample (don’t do this in schools due to danger of infection).

Link to the article: Help Your Microscope with Stains and Reagents (Popular Science, March 1937)

Method:

1. Cut the potato in half and scrape a little of the potato onto the microscope glass slide. This can be done either with a knife or with the fingernails. There should not be any large potato pieces on the glass.
2. Place a small drop of water on the “potato juice” and then place the glass cover slip on top.
3. Observe using the microscope. The starch grains will be visible as oval structures.
4. Now dilute a small amount of iodine in some water. The water should only turn slightly yellow. Place a drop of the dilute iodine next to the glass cover glass, so that some of the solution is able to flow between the cover glass and the slide.
5. You should be able to see how the starch grains change color. The iodine will react with the starch and turn it blue-black.
6. Alternatively, you can observe the starch grains in dark field or in polarized light (without adding iodine): Darkfield Microscopy | Simple Polarization Microscopy | Potato Starch Grains