Blue-violet pigments in neutralizing shampoos act through chromatic subtraction: their molecules absorb the yellow-orange wavelengths (580–600 nm) reflected by bleached hair, visually neutralizing unwanted tones. This mechanism is based on the law of complementary colors — violet (430–380 nm) is the complementary color of yellow — and not on a chemical reaction with melanin.
Chemistry of Direct Pigments: Crystal Violet and Anthraquinones
Neutralizing pigments belong primarily to two chemical families. Crystal violet (CI 42555) is a triphenylmethane dye with a molecular weight of 407.98 Da, soluble in aqueous-alcoholic media, with a maximum absorption at 590 nm. Anthraquinones (Ext. Violet 2, CI 60730) are synthetic pigments with higher photostability, oxidation-resistant, with absorption centered at 600–620 nm. In both cases, the molecule must be small and polar enough to penetrate the interstitial spaces of the opened cuticle of bleached hair.
Deposition Mechanism on the Porous Fiber
Oxidative bleaching opens the cuticle scales and increases the differential porosity of the fiber. This increased porosity facilitates adsorption of direct pigments through electrostatic interaction and passive diffusion into the cortex. Fixation depends on three variables: pigment concentration (typically 0.001–0.05% in the formulation), shampoo pH (ideally 4.5–5.5 to close the cuticle after deposition) and contact time (2–5 minutes for moderate effect, 10–15 minutes for intense effect). Excessive contact time on highly porous hair risks over-pigmentation, visible as a persistent violet cast.
Professional Application Rules
The professional must adjust frequency to the porosity level of the fiber. On hair bleached above 60%, use 1–2 times per week. On very porous or fine hair, alternate with a neutral shampoo to prevent pigment buildup. Rinsing should be thorough with lukewarm water to close the cuticle and set the deposited pigment. Combined use with a neutralizing mask amplifies and extends the effect up to 72 hours. Hairswiss notes that violet shampoos do not replace a salon bleach maintenance — they maintain a result, they do not correct it.
Professional Product Available on cliCHair
The No Glow Yellow Shampoo 300, available on cliCHair.ch, incorporates blue-violet pigments at calibrated concentration in a sulfate-free base. Its acidic pH promotes cuticle closure after neutralization, limiting the risk of over-pigmentation. Use alternating with a moisturizing shampoo on the most fragile hair.