Defects that may be visually observed and treated as beauty defects are caused during the production of raw materials and element surfaces, coating processes, and handling. The main defects that appear on optical elements are as follows:

• Blister: an inclusion or bubble under or within a coating that lifts the film.
• Breakage: a large edge chip on an optical element.
• Bubble: a gaseous inclusion in an optical material.
• Chip: an area on an optical material that has broken away from a surface, edge (edge chip), or bevel.
• Crack: a fracture in the film (coating) or substrate of an optical element.
• Dig: a small rough spot on a surface, similar to a pit.
• Digestion: some kind of defect made by a chemical or environmental force.
• Dirt: a stain on an optical surface (coated or uncoated) that can be removed by standard cleaning procedures without damaging the surface.
• Discoloration: different colors of coating on the same surface.
• Dust: a number (often numerous) of small pieces of matter on a film.
• Fingerprint: unique oily pattern that remains on an optical surface after touching it with a bare finger.
• Flaking: partial separation of film(s) originating from the inner region of a coated area.
• Milkiness: cloudy areas within a optical material.
• Mold mark: marks on the surface produced by molding.
• Orange peel: a lens surface that has been improperly or insufficiently polished, which resembles the skin of an orange.
• Particle: a small piece of matter on/in a film.
• Peeling: partial separation of thin film(s) originating from the peripheral zone of a coated area.
• Pinhole: a very small hole in a thin film.
• Rub: a series of small surface scratches, generally caused by mishandling.
• Run-ins: cement separation at the edge of a cemented component.
• Scratch: marking or tearing on a surface caused by either a sharp or rough instrument.
• Sleek: a hairline, very fine scratch.
• Smear: residue of evaporated or unevaporated moisture.
• Spatter: imperfections that result when small chunks of coating material land on the substrate surface and adhere during the coating process.

Stain: a discolored spot or area (possibly caused by chemical reactions).

Stone: an opaque inclusion in an optical material consisting of
undissolved or crystalline material.

Striae: an internal imperfection of glass that appears as a wavy distortion. Only heavy striae may be observed with the unaided
eye.

Water spot: a spot that remains on the surface after water evaporates.