Specimen preparation involves several steps:
- Fixing: This kills the cells and preserves the specimen. The fixing solution is water-based and a wide range of different solutions exist
- Dehydration: The water in the specimen is slowly removed by placing it into subsequently higher concentrations of alcohol
- Infiltration: The alcohol is removed and replaced with a solvent which is compatible to the embedding medium (usually paraffin). Often xylene is used.
- Embedding: The specimen is now embedded into paraffin. The paraffin block supports the specimen during microtoming.
- Mirotoming: The specimen (in paraffin) is now cut into thin sections.
- Mounting: The paraffin has to be removed and the specimen is then mounted in appropriate mounting medium
If the specimen contains water (and this is the case for most specimens), then it has to be first dehydrated by placing it into subsequently higher concentrated alcohol. If Euparal is used as a mounting medium, then it is possible to directly transfer the specimen into this mounting medium. If other solvent based mounting media are used, then it is necessary to first infiltrate the specimen with the solvent xylene (which is harmful when inhaled). Water based mounting media, such as Glycerol Jelly, can be used to directly mount specimens which are not completely dehydrated.