Mounting media can be classified into aqueous (water based) mounting media and solvent based media. Specimens that are to be mounted in solvent based mounting media must be completely free of water. A common water-based mounting medium is Glycerine gelatin. This medium can easily be made at home, but is difficult to use. Bubbles are common and the slide has to be warmed during the mounting process to keep the medium fluid. Solvent based mounting media sometimes contain harmful organic solvents, which might make these media less suitable for amateur use.