Staining paint is a term generally used in two contexts: an artistic technique where thinned paint is used to saturate a surface, and a pigment property in watercolor painting. 

1. Stain Painting (Artistic Technique):

In fine art, specifically the Color Field Painting movement of the 1950s and 60s, staining paint refers to a technique where artists dilute oil or acrylic paint with large amounts of solvent (like turpentine or water). 

Application: The thinned paint is poured or brushed onto raw, unprimed canvas.

Result: Instead of sitting on top of the surface as a solid film, the paint is absorbed into the fibers, becoming an integral part of the fabric.

Visual Effect: This creates a luminous, watercolor-like effect that emphasizes pure color and texture over brushstrokes or representational forms.

Key Artist: Helen Frankenthaler is widely credited with pioneering this “soak-stain” method. 

2. Staining vs. Non-Staining (Watercolor):

In watercolor painting, “staining” describes a physical property of certain pigments rather than a method of application. 

Staining Pigments: These pigments (such as Phthalo Blue or Alizarin Crimson) have tiny particles that settle deep into the pores of the paper. They are difficult or impossible to “lift” (remove) once dry.

Non-Staining Pigments: These pigments have larger particles that sit on the surface of the paper fibers. They can be easily re-wet and scrubbed off with a brush to reveal the white paper underneath. 

Comparison: Stain vs. Traditional Paint

Feature	Traditional Paint	Stain / Staining Paint
Binder Content	High; creates a thick surface film	Low; mostly solvent and pigment
Interaction	Sits on top of the substrate	Penetrates into the substrate
Opacity	Generally opaque; hides the material underneath	Translucent; highlights natural grain or texture
Failure Mode	May peel, crack, or flake over time	Tends to fade rather than peel

Other Contexts:

Wood Finishes: Often simply called “wood stain,” these products are designed specifically for porous materials to add color without obscuring the wood grain.

Paint Defects: In home maintenance, “staining” can refer to unwanted discoloration (like tannin bleed) that seeps through a finished paint coat.