Start from the pigment surface, not the binder
Dispersant selection is driven first by the pigment surface. Inorganic pigments such as titanium dioxide and iron oxides have polar, high-energy surfaces with plenty of anchoring sites, and are relatively easy to stabilise with modest dosages of polyacrylate-type dispersants.
Organic pigments and especially carbon black are a different problem. Their surfaces are less polar and offer fewer anchoring points, while their specific surface area is far higher. These require dispersants with multiple anchoring groups and substantially higher dosage calculated on pigment weight, not on total formulation.
Choose the stabilisation mechanism
In solventborne systems, steric stabilisation dominates: the dispersant must provide polymer chains compatible with the solvent and binder, extending far enough from the particle surface to prevent approach. Molecular weight and chain compatibility are the critical variables.
In waterborne systems both electrostatic and steric mechanisms are available, and the most robust products use both. Purely electrostatic stabilisation is vulnerable to electrolyte and pH shifts, a common cause of viscosity instability that appears weeks after production rather than in the lab.
Dose on pigment, not on formulation
The single most frequent dispersant error is dosing on total formulation weight. Dispersant demand is a function of pigment surface area, so it must be calculated on pigment weight. Titanium dioxide might need 0.5–2% on pigment; a high-surface-area carbon black can need 30–40% or more.
Underdosing gives incomplete surface coverage, leaving bare patches that bridge particles together and produce flocculation, viscosity rise and colour loss. Overdosing leaves free dispersant in the water phase or binder, which can cause water sensitivity, foam stabilisation and reduced film hardness.
Evaluate against your actual objective
Optimising for grinding speed, colour strength and storage stability does not always converge on the same product. A dispersant that reaches target fineness fastest may not be the one that holds viscosity through three months of warehouse storage.
Decide the priority before screening. Then measure it directly: colour strength by let-down against a standard, grinding efficiency by time to target fineness, and stability by viscosity and fineness after accelerated storage. A rub-out test on the drawdown is the fastest indicator of flocculation and takes almost no time. It should be routine in every screening.
Apply this to your own formulation
Send us the binder system, substrate and the defect you are seeing. We will suggest a specific grade and dosage range.