Coverslipping and mounting media

Glass coverslips are used to protect specimens from physical damage and to keep them from drying out when exposed to air after staining.  The coverglass is mounted with either an aqueous media or, more commonly, a permanent resinous media.  In recent years, natural resins, such as Canada balsam and gum dammar, have been replaced with synthetic resins because they dry faster, are neutral in reaction and remain clear with age.  The refractive index of the mounting media should be close but not identical to the refractive index of the glass slide, coverslip, and cleared specimen, which is normally around 1.53 to 1.54.

 

Resinous media are made by dissolving solid resins in a solvent, usually toluene, until a viscosity is reached that allows the media to flow across the slide and specimen evenly, filling spaces without creating air bubbles.  Mounting medias harden as the diluent evaporates, which is desirable on the coverslipped slide but not in the stock solution.  If the stock solution becomes too thick, it can be diluted by adding small amounts of diluent and gently stirring until it runs freely.  If it is too thin, it will pull away from the edges of the coverslip as the excess diluent evaporates and, in extreme cases, allow air bubbles to reach the specimen area.  In that case, the coverslip should be soaked off and a new one applied using media of the correct viscosity.

 

Slides mounted with media of the correct viscosity can be safely viewed microscopically within 10 to 15 minutes but they should be stored horizontally until they are completely dry.

 

Acrymount™ (CAT# SL80) is a rapid drying mounting medium/liquid cover slip that is soluble in both xylene and toluene.  Slides mounted with Acrymount™ may be screened in as few as 10 minutes.  It is available in a 16 oz bottle.

 

M1™ (CAT# SLM180) is similar to Acrymount™ but it is thinner and dries faster.  It is especially useful as a liquid coverslip.  It is also available in a 16 oz bottle.

 

Mounting Medium T (CAT# 57006-16) is a synthetic resin dissolved in Toluene.  It is compatible with xylene and XS-3.  It has a low viscosity making application easier and reducing bubbles.  It is available in 16 oz bottles.