Some mounting media oxidize rapidly upon exposure to air, forming carboxyl groups. This can be more pronounced when sections have been cleared in a solution containing aldehyde. It is sometimes observed that the immunogold/silver signal fades after a few weeks, or even in a shorter time, from sections that have been mounted with these media under cover slips. The silver is still present, but has formed translucent silver carboxylate salts. Visibility can be retrieved by removing the cover slip and washing in xylene and then immersing the slide in photographic developer, but this is a tedious procedure. BIOMOUNT is a specially formulated mounting medium that reduces fading of immunogold/silver signals in sections on glass slides. It is suitable for resins as well as wax embedded sections of tissue.