Diatoms make for beautiful specimens for both transmission and scanning electron microscopy. As well, they are studied by many people, and there is always a need for good diatom preparations for EM.I find that the diatoms in diatomaceous earth are usually broken, and like to prepare my own from fresh specimens. The materials needed for this are a plankton net, some potassium dichromate, and 30% hydrogen peroxide. Once the diatoms are collected (plankton net tows from shoreline, or wherever), they can be cleaned using the chemicals.