In light microscopes and TEMs the beam of light/electrons passes through the object being viewed.
An image is produced because some parts of the object absorb more light than others.
Sometimes the object is completely transparent which makes the whole thing look white because the light rays/electrons pass straight through it.
To get around this issue, the object can be stained:
Light Microscopes:
- use dye - the most common stains are methylene blue or eosin
- the stain is taken up by some parts of the object more than others - the contrast makes different parts show up
Electron Microscopes:
- objects are dipped in solution - heavy metals, like lead
- the metal ions scatter the electrons, again creating contrast
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