Leather

Spews

Fatty spews

Fatty spews are fatty or greasy materials which migrate to the leather surface. The materials which migrate to the surface are either solid fats or products of the acidic breakdown of solid fats.

These fatty materials are often present in lubricants used to soften leather. Neatsfoot oil, unless specified as cold-tested, contains a considerable amount of fatty materials. Leather dressings containing neatsfoot oil are a potential source of these spews.

Gummy spews

Gummy spews arise when oils—particularly fish oils—used to lubricate leather, degrade to their constituent fatty acids. These substances migrate to the surface of the leather, where they appear as gummy or resinous deposits. They are unpleasant to touch and handle.