Cotton Blue

Cotton Blue is a water-soluble biological stain, also known as aniline blue (water-soluble), appearing as a dark blue to dark brown powder used primarily for staining fungal cell walls (chitin/cellulose) and collagen fibers in microscopy.​

Identity and Composition

Chemical name: Aniline blue (cotton blue, water-soluble; CI 42755).​

Molecular formula: Complex triarylmethane dye mixture, typically C₃₁H₂₇N₃Na₂O₉S₃ or similar; molecular weight ~737 g/mol.​

Grade specifications: Microscopy grade with absorption maxima 595–610 nm, ratio λmax.P ±15 nm 1.00–1.03, soluble in water.​

Physical Properties

Appearance: Dark blue/black powder or crystals, odorless.​

Solubility: Soluble in water; often prepared as 2.5% solution in 2% acetic acid or used in Lactophenol Cotton Blue mounts.​

Stability: Light-sensitive in solution; store powder in dark.​

Typical Uses

Fungal microscopy: Stains hyphae, spores, and structures blue in Lactophenol Cotton Blue (LPCB) mounts.​

Histology: Collagen blue in Masson's trichrome stain; cellulose walls and chromosomes in plant tissues.​

Other: Paper/textile dyes, fluorescence microscopy with KOH.​

For catalog purposes: “Cotton Blue (aniline blue water-soluble), dark blue powder, microscopy grade, λmax 595–610 nm, for fungal/collagen staining; water-soluble.”​