Pigment Surface Treatment: Coated or Not

Two pigments with the same colour index can behave completely differently in the same formula, because one has a surface coating and the other does not. Treatment affects dispersion time, coverage, water resistance and cost, and it is the variable buyers most often leave unspecified when they approve a shade.

1. Why pigments are coated

Raw pigment particles tend to clump and to resist wetting by the oil or water around them. A surface treatment changes the chemistry at the particle boundary, making it compatible with a chosen vehicle. Untreated pigment in a water-based formula often foams, sediments or leaves streaks that no amount of milling fixes.

2. The common treatments

Typical treatments include silicone coatings such as dimethicone or methicone, silane coupling agents, metal soaps, and hydrophilic treatments for water-borne systems. Each shifts the pigment’s wetting behaviour. Silicone treatment improves slip and water resistance, while a hydrophilic treatment makes a normally oil-loving pigment dispersible in water.

3. Dispersion and wetting

Treated pigments usually wet out faster and reach a stable dispersion at lower shear. That shortens milling time and reduces the heat the batch sees. In practice this is where most of the cost difference is recovered: a treated pigment that mills in half the time can be cheaper per batch despite a higher price per kilogram.

4. Coverage and the white cast

Coating thickness affects how much light the particle scatters. Over-treated titanium dioxide or zinc oxide can read less opaque and require a higher load for the same coverage. In sunscreen and tinted products, that load then changes texture and cost. Ask for the treatment level as a percentage, not just the treatment type.

5. Water resistance and wear

Silicone-treated pigments generally improve water resistance and wear because the coating reduces water wetting at the surface. This is why the same shade can perform well in a cream and poorly in an emulsion foundation. The treatment and the vehicle have to be chosen together, not sequentially.

6. Cost and lead time

Treated pigments typically cost 20 to 60 percent more than untreated grades and often carry longer lead times because fewer suppliers hold stock. For a first order, that lead time can decide the launch date more than the price does. Confirm minimum order quantities before specifying a treated grade into a brief.

7. Compatibility with the vehicle

Treatment chemistry must match the continuous phase. Silicone-treated pigment in a silicone-based anhydrous formula disperses easily; the same pigment in a glycerin-rich gel may not. Mismatches show up as viscosity drift over weeks rather than as an obvious defect, so they are easy to miss in a two-week sample trial.

8. Testing that separates suppliers

Ask for a drawdown at a fixed pigment load on the same base, a fineness of grind reading, and a viscosity measurement at day one and day thirty. Then measure colour after accelerated storage. Two suppliers quoting the same colour index can differ by a visible margin on all four tests.

9. When uncoated is right

Untreated pigment remains sensible in pressed powders, where the binder system already wets the particle, and in products where cost per kilogram dominates. It also avoids treatment-related interactions in formulas with unusual solvents. The decision should follow the vehicle and the process, not a general preference for treated grades.

10. Where it fits

Pigment behaviour matters in tinted creams and in brightening lotions. See materials notes and product formats.