Smearing

Smearing refers to the act of spreading a substance over a surface to form a thin, often irregular layer. A smear can be intentional, as in preparing a sample for analysis, or incidental, as a residue that remains after contact with another object. The resulting deposit is called a smear and may be studied or removed depending on context.

In biology and medicine, smear techniques create a uniform layer of cells or microorganisms on a microscopic slide for staining and examination. A common example is a bacterial smear prepared from a sample and stained (such as Gram staining) to reveal morphology. Blood smears or smear cytology are used to assess cell types, counts, and abnormal forms. The thickness and distribution of the smear affect staining quality and interpretation.

In materials science and physics, smearing denotes a smoothing operation. In lattice gauge theory, quark or gauge fields are smeared to reduce ultraviolet noise and highlight longer-range structures; methods include Gaussian or Jacobi smearing. In image processing and data analysis, kernel smoothing or moving-average smearing reduces noise and reveals trends but can blur fine detail.

In dentistry, a smear layer refers to a thin layer of debris formed on dentin during cavity preparation, which can affect bonding of restorative materials.

In social and political contexts, smearing can describe the act of damaging someone's reputation through unverified or misleading allegations, often associated with smear campaigns.