Optical Adhesives Lens separations or bond failures can be divided into two types, adhesive and cohesive. Identifying which of these two types of failure is occurring will determine what steps to take to prevent them. Adhesive failure occurs when the cement separates from the glass surface. It is seen as a shiny area in reflected light. It can be any shape and can be identified by the presence of Newton rings, or a color fringe.
Cohesive failure occurs when the cement pulls away from itself.
This can be identified by the fern-like voids, called feathering, appearing along the edge of the lens or sometimes in the interior. When this type of failure does occur it is usually caused by a lack of cleanliness of the glass surfaces. If there is a trace of oil, fingerprints, dirt or any contamination between the cement and the glass there is a potential for adhesive failure. The solution for this is to look closely at the cleaning process. Things like contaminated solvents or improper handling could be the cause.