Bloom is a coating defect defined by dull, non-homogeneous or shady appearance caused by the accumulation of non-transparent oils or wax-like substances on the surface of the coating. 

This problem is often difficult to create in the laboratory environment; problems often arise during storage of painted surfaces, during their use in the field, or during exterior strength tests. To re-create this problem in the lab, cycle tests involving temperature, humidity, and cooling are needed. This problem might be caused by the migration of an oil, a plasticizer, or an uncrosslinked component to the surface. Appropriate solution for this problem usually requires the removal the migrating component or material from the paint. The most difficult part of solving this problem however, is identifying the material that comes to the surface and to determining its source in the paint formula. The most common sources of bloom are non-functional low molecular resin inputs, poorly soluble plasticizers or other additives, waxes and lubricants. A good analysis laboratory is a valuable asset in identifying the problem causing the bloom.