Diatoms are used in many manufactured products that we use every day. One of these products is toothpaste. With a smear of toothpaste on a slide, you may be able to see diatoms with your Foldscope. Take a look at this website (http://www.truevisionmicroscopes.com/everyday-objects-under-a-microscope-examining-toothpastes-and-white-chalk.html) to see that you should be able to see diatoms in your toothpaste. Your slide mounts may require some trial and error, but when you get the thinness of toothpaste just right, you will be delighted to see diatoms with your Foldscope! See https://microcosmos.foldscope.com/?p=2804 for a general view of toothpaste.
Diatoms are microscopic (to nanoscopic) bits of silica glass that are used as a fine abrasive in toothpaste to clean teeth. Another source of diatoms is tooth powder. You will need to add a drop of water to your slide and add a bit of the powder to make a thin strew mount. Again, experimentation and patience is all it will take to enable viewing the diatoms.
The kinds of diatoms that are used in toothpastes and tooth powders usually comes from large diatomite deposits. In the United States, the largest marine deposit of diatomite is in Lompoc, California, and there are many diatomite mines throughout the western states. Here’s a general document on diatomite and some of its uses and economic worth (http://minerals.usgs.gov/minerals/pubs/commodity/diatomite/250400.pdf). The USGS has a number of documents available on the web on diatomite for additional information.
Who would have thought that an organism that is so very small is also so very important to our everyday hygiene? Diatoms play an important part in our lives—find information on other products that contain diatoms. You might be able to make slides of these products to view diatoms as well!