A calcium carbonate specification sheet can list twenty numbers. If you only have time to check two, check these: brightness and the impurity pair Fe₂O₃/SiO₂. One decides what your customer sees. The other decides what your equipment feels.
Brightness: the visible number
Filler typically enters a formulation to displace something more expensive — premium pigment in paint, fiber in paper, polymer in plastics. The catch: if the filler is dull, the formulation pays it back in extra titanium dioxide or extra pigment to recover the lost whiteness. A brighter filler is not a cosmetic luxury; it is a direct line in your cost calculation.
Our grades run at 97% brightness, verified by optical testing on every production batch — so the whiteness you qualified in the lab is the whiteness in every delivery.
Iron oxide: the slow surprise
Fe₂O₃ is the impurity that tints. Even trace iron shifts a bright white powder toward cream and yellow — subtly at first, then visibly as loadings climb. Worse, iron content varies with the limestone source, so a filler that looked fine at qualification can drift batch by batch if the deposit isn't clean.
Our chemistry holds Fe₂O₃ at 0.001% — one part in a hundred thousand — which is why the 97% brightness figure holds steady.
Silica: the abrasive tax
SiO₂ — quartz — is dramatically harder than calcite. In a filler it acts as a slow grinding compound inside your own equipment: extruder screws, dies, mixer blades, wire-drawing tooling. The damage never appears on a delivery note; it appears months later in the maintenance budget.
At 0.001% SiO₂, our GCC is a very low abrasion filler — the reason it's specified in rubber and cable compounds where tooling wear is watched closely.
What to do with this
- Ask for brightness as a verified batch value, not a range on a brochure
- Ask for Fe₂O₃ and SiO₂ explicitly — "99% pure" says nothing about which 1% is missing
- Qualify against the numbers, then hold deliveries to them