Embrittlement (of O-rings). Partial loss of the elastic properties of the elastomer results in loss of adaptability and hence sealing capability. The cause of embrittlement is usually thermal overloading of the material, often combined with a simultaneous chemical attack. Embrittlement can be recognized not only in the partial loss of elasticity and an increase of hardness, but also in the mostly fine, radial cracks mainly in the area of the contact faces. Often these cracks do not become visible until the O-ring is twisted.