Getting to Primary Particles
A pigment as manufactured is a powder of primary particles that have clumped into aggregates (particles fused face-to-face) and agglomerates (particles loosely stuck edge-to-edge or corner-to-corner). None of that clumped powder is usable until it's broken down and locked into the medium — the process of dispersion, which happens in three stages:
- Size reduction — breaking the larger aggregates and agglomerates back down into primary particles, using impact and shear force
- Wetting — uniformly spreading the liquid medium or resin over the pigment surface
- Stabilization — keeping the now-separated particles from re-agglomerating and coming back together Get any one of the three wrong and the paint, ink or plastic pays for it in weaker colour, poorer gloss, or grit.
What's Measured
For decorative paints in particular, a handful of physical properties are tracked on every pigment batch:
- Particle size — reported as a mean/average size and a distribution, in the range of roughly 0.1–10 microns for most pigments. It's the single biggest driver of opacity, tinting strength and light fastness. It's measured with laser-diffraction particle-size analysers (Fraunhofer/Mie theory, 0.2–500 microns) and, for the finest end, by dynamic light scattering (0.3 nm–5 microns).
- Surface area — directly tied to particle size: small particles carry a large surface area, big particles a small one. Measured by BET surface-area analysers.
- Oil absorption (OA) — per ASTM D281, the amount of oil a given weight of pigment needs to form a paste of standard consistency. OA is affected by particle size and surface area, and tells a paint formulator how much oil or resin is needed to wet the entire pigment surface.
- Bulk density — grams of pigment per cc of volume; besides describing the powder, it tells you how much shipping/storage space a given weight will take up.
- Bleeding — pigments are technically insoluble in their application medium, but in practice many dissolve slightly. Inorganic pigments bleed less than organic ones; bigger particles bleed less than smaller ones. Bleeding is assessed visually and rated 1 (poor) to 5 (best).
Head-to-Head
Two pigments in the same Colour Index family can still trade off shade, strength and opacity — which is exactly why side-by-side comparison sheets matter when picking a grade:
|
Parameter |
PY 151 |
PY 154 |
|
Colour shade |
Greener |
Redder |
|
Colour strength |
100% |
71% |
|
Opacity (contrast ratio) |
64.0 |
47.17 |
|
Overspray fastness |
5 |
5 |
|
Parameter |
PY 83 |
PY 139 |
|
Colour shade |
Greener |
Redder |
|
Colour strength |
100% |
99% |
|
Opacity (contrast ratio) |
67.46 |
77.0 |
|
Overspray fastness |
4–5 |
5 |
|
Parameter |
PY 110 |
PY 139 |
|
Colour shade |
Redder |
Greener |
|
Colour strength |
100% |
118% |
|
Opacity (contrast ratio) |
49.20 |
77.0 |
|
Overspray fastness |
5 |
5 |
Read together, these three tables make the point: shade, strength and opacity don't move together, so the "best" pigment in a family depends entirely on what the application needs — maximum strength, maximum opacity, or a specific shade.
Portfolio
Sudarshan is India's leading pigment producer and a supplier to the plastics, paints and inks markets globally, with over 60 years of manufacturing experience and sales in more than 60 countries. Its range is organised around four positions and matching chemistries:
- General purpose — lead chromates, azos, naphthols
- Performance — isoindolinones, benzimidazolones, DPP, quinacridones, azo condensations, phthalos
- Traditional — cadmium, iron oxides
- Eco-friendly — organic alternatives free of the heavy metals above
These map onto the brand families used across the business — Sudaperm, Sudafast, Sudadur, Sudacolor, Sumica and the Effect pigment range — each positioned against a different combination of performance and cost.
Weathering
Two accelerated-weathering instruments cover the standard light-fastness and weather-fastness tests:
- QUV — tests light fastness by exposing samples to UV radiation (200–400 nm, with the UV-B band at 280–315 nm) at an irradiance of 0.65 W/m², cycling 4 hours of light with 4 hours of dark.
- Ci 4000 (Xenon) — tests both light fastness and weather fastness by reproducing the full spectrum of sunlight and rain (290–800 nm) at 0.5 W/m² irradiance, 50% relative humidity and a 40°C chamber temperature.
Results are read against reference scales: light fastness on the Blue Wool scale, 1 (poor) to 8 (best); weather fastness on a grey scale, 1 (poor) to 5 (best). One caveat worth keeping in mind: there's no single correlation factor between hours of exposure in an artificial weathering test and real outdoor weathering. The reliable way to correlate the two is to expose matched panels — one set in the weather-o-meter, one set outdoors — and build the correlation from what's actually observed.