The choice of mounting medium is largely dependent on your sample type, how you will image, and which fluorophore or fluorescent proteins you use. An ideal mounting medium should:

• Have refractive index as close as possible to that of the fixed protein (tissue)
• Be colorless, transparent with only the stained tissue elements visible
• Not shrink back from the edge of cover-glass
• Be able to completely permeate and fill tissue interstices without any adverse effect on tissue components
• Be resistant to contamination particularly microbial growth
• Protect the section from physical damage and chemical activity (oxidation and changes in pH).
• Be completely miscible with dehydrant or clearing agent and remain stable once set.
• Not react with, leach or induce fading in stains and reaction products.