How to Qualify a New Calcium Carbonate Supplier: Reading the COA, Checking the TDS, and Running a Sample Trial

In short: You qualify a new calcium carbonate supplier in two steps — on paper, then on your line. On paper: check the per-lot COA against the TDS, focusing on five parameters — whiteness with its measurement method, the D97 top cut, CaCO₃ purity, iron, and (for coated grades) coating level and moisture. On your line: run a free sample through your own QC and process, and if it holds, take one trial container parallel to your current supply before committing. This guide gives you the checklist and the reject rules, so a new supplier proves itself before a container is at risk.

A new supplier sends a clean-looking spec sheet and a good price. The first container arrives. On the line, the white film carries a faint grey cast the current grade never had, or specks appear in a thin gauge. Nothing was faked — the grade simply was not what your line needed, and no one checked the actual lot data before it shipped.

Two mistakes cause almost every case:

• Reading the TDS and never checking the COA. The data sheet says the grade should be whiteness 98 and fine; the lot you received is a different story, and only the COA tells you the difference.
• Not getting a COA until the goods have landed. By then the container is paid for and in your warehouse — too late to reject.

Qualifying a supplier is how you avoid both. It is a paper check, then a line check, and it costs you a few minutes and a sample — far less than one off-spec container.

These are two different documents doing two different jobs. Keep them separate and the qualification becomes simple.

The TDS is the menu; the COA is the inspection result for the plate in front of you today. A supplier worth qualifying gives you both — and a per-lot COA, not the same nominal numbers reprinted every shipment.

Not every line on a COA carries equal weight. These five, in order of impact, decide whether a GCC lot performs:

1. Whiteness and ISO brightness — with the method stated

This is the first thing to check and the easiest to be misled on. "Whiteness 98" means nothing until you know how it was measured — whiteness can be reported on several scales (Hunter, CIE, the Chinese GB/T scale), and the same powder scores differently on each. ISO brightness (R457 / ISO 2470) is the single method-defined number that is comparable between suppliers.

• What to require: both figures, each with its method named. A COA that says "whiteness 98" with no method is a soft claim; one that says "whiteness ≥98 / ISO brightness 95.6 (R457, ISO 2470)" is a checkable one.
• Reject rule: if the method is not stated, ask for it before you compare anything. A whiteness number without a method is not comparable to your current grade. (Full explanation: whiteness vs. ISO brightness.)

2. The D97 top cut — not the average

The number that predicts film specks, gels, and screen blockage is not the median (D50) — it is the D97 top cut, the size below which 97% of the particles fall. Defects come from the coarse tail of the distribution, not the average particle. Two lots can share a D50 and behave very differently if one has a longer coarse tail.

• What to require: the D97 (and D50), measured on a named laser method (for example a Malvern laser sizer). Match the D97 to your product's thickness — the thinner or more surface-critical the product, the tighter the top cut it needs.
• Reject rule: a COA that lists D50 only and hides the D97 is hiding exactly the number that causes defects. Ask for the D97 before you trial the lot. (How to match top cut to your product: which grade for your application.)

3. CaCO₃ purity and acid-insoluble residue

Purity confirms you are getting calcium carbonate, not a diluted or contaminated powder. Acid-insoluble residue (the fraction that will not dissolve in acid) is the practical measure of the grit and silica that grind your screens and mar surfaces.

• What to require: CaCO₃ purity (a premium grade runs ≥98%) and a low acid-insoluble figure. Compare against the TDS.
• Reject rule: purity well below the TDS, or a rising acid-insoluble figure lot to lot, signals a change in the ore or the milling — ask the supplier before you accept.

4. Iron (Fe₂O₃) — the parameter that predicts whiteness drift

Iron is what yellows a filler. A grade can pass on whiteness the day it is tested and still drift, lot to lot, if the iron content moves. Low iron is what keeps whiteness stable across shipments.

• What to require: Fe₂O₃ reported on every COA (a premium grade runs ≤0.05%). It is the parameter that predicts whether lot 14 will match lot 1.
• Reject rule: iron not reported at all is a gap on any premium-grade COA. Iron drifting upward across lots is an early warning before whiteness visibly falls.

5. Coating level and moisture — for coated grades

If you buy a stearic-acid-coated grade, two more numbers drive whether it disperses cleanly: the coating level (typically around 1% by weight for a standard fine GCC, higher for ultrafine) and moisture. Over-coating shows up as screw slip and plate-out; high moisture causes voids and surface defects.

• What to require: coating level and moisture on the COA for coated grades; confirm the coating is what your process expects.
• Reject rule: high moisture (well above the TDS) is a shipping- or storage-quality signal — raise it before the lot runs. (When coated is the right choice at all: coated vs. uncoated calcium carbonate.)

One parameter to add only when it applies — heavy metals. If your end product is food-contact (opaque white bottles, caps, closures), the qualifying gate is not whiteness — it is an accredited heavy-metals panel (lead, arsenic, cadmium, mercury) and a food-contact declaration. Ask for it specifically for food-contact work; for ordinary industrial filler it is not required.

The right sequence (before the container ships):

1. Confirm the order — grade, and that the material is produced to a named spec.
2. Ask for the COA before shipment — the supplier sends the per-lot COA as a scan.
3. Check the five parameters against the TDS — using the table below. If all are within tolerance, confirm the shipment.
4. If anything is out of spec — ask for a different lot, or negotiate on the off-spec lot before it ships.
5. Goods ship — the original COA travels with the documents (B/L, Form D / e-Form D, invoice).

The wrong sequence (common, and expensive):

Order → goods ship → COA arrives with the documents → container lands → check the COA → find it out of spec → too late to reject.

The difference is a few minutes of checking before the container is at risk, versus the cost of handling an off-spec container after it has landed — return freight, a claim negotiation, and the waste of a failed production run.

Use this every time you receive a COA from a new supplier:

If any row fails: raise it with the supplier before you confirm the shipment. Ask for a replacement lot or agree terms on the lot in hand.

Paper qualifies the lot; your own line qualifies the supplier. Once the COA checks out, prove it where it counts:

1. Free sample (under a tonne). A serious supplier sends a qualifying sample at no cost, with the per-lot COA. Confirm whiteness and top cut on your own equipment first — do not simply trust the printed numbers.
2. Run it in your real process. Put the sample through your actual line against your current grade, at your loading and conditions. Watch whiteness, surface, dispersion, and reject rate.
3. On a white line, run the titanium-dioxide step-down. A whiter filler is worth its higher price only when it lets you remove pigment. Step your TiO₂ down in stages and measure whiteness and opacity at each step to find your ceiling — the method is in how much titanium dioxide calcium carbonate can replace, and the pigment you displace is usually worth far more than the difference in filler price (filler economics calculator).
4. One trial container, parallel to current supply. If the sample holds, take a single container alongside what you run today — not a switch. It proves landed cost and line performance on a real shipment, with your current supply still in place if anything falls short.
5. Then decide. A supplier that clears the paper check, the sample, and the trial container has earned a program. One that fails a check has cost you only sample time.

Put the checks together and the qualifying supplier has a clear profile: a per-lot COA with lot number and production date, methods named beside every figure (ISO 2470 for brightness, a named laser method for particle size), iron and purity reported as standard, a free qualifying sample, and a willingness to run one trial container parallel to your current supply. That profile is exactly how we supply the KC Series — whiteness ≥98 and ISO brightness ≥95 (R457 / ISO 2470), CaCO₃ ≥98%, Fe₂O₃ ≤0.05%, coated or uncoated, with a per-lot COA on every shipment.

One honesty note, because qualification is about checkable claims: the KC Series COA today reports whiteness, brightness, and particle size (on a Malvern analyser) to our current spec; a heavy-metals panel at an accredited laboratory is in progress and will be added to the COA once complete, which matters only if your end-use is food-contact.

If you want to qualify us against your current grade, send your application, the spec you run today, and — if your line is white — your TiO₂ loading, and we will recommend a grade and send a free sample with its per-lot COA to check on your own line before you commit to anything. Start from the product page.

What should a calcium carbonate COA show?

A per-lot COA shows the actual measured values for that specific lot — with the lot number, production date, and the test method beside each figure. For GCC the parameters that matter most are whiteness and ISO brightness (method named — ISO 2470 / R457), D50 and D97 particle size, CaCO₃ purity, iron (Fe₂O₃), and for coated grades the coating level and moisture. A COA that just reprints the TDS nominal figures with no lot number is not a real certificate of analysis.

What is the difference between a TDS and a COA for calcium carbonate?

The TDS is the grade's nominal specification (updated rarely); the COA is the measured result for one specific lot (issued every batch). The TDS tells you whether the grade fits your application; the COA confirms the lot you are receiving is in spec. You qualify a supplier by checking the COA against the TDS, lot by lot.

Which calcium carbonate parameters matter most when checking a lot?

Five: whiteness and ISO brightness (only comparable if the method is stated); the D97 top cut (defects come from the coarse tail, not the average); CaCO₃ purity and acid-insoluble residue; iron (Fe₂O₃), which yellows filler and moves whiteness lot to lot; and for coated grades the coating level and moisture.

How do I run a calcium carbonate sample trial?

Qualify on paper first (COA vs. TDS). Then run a free sample under a tonne on your own line and QC — confirm whiteness and top cut on your own equipment, then run it in your real process against your current grade, stepping TiO₂ down on a white line. If it qualifies, take one trial container parallel to your current supply before committing to a program.

What are the warning signs of a calcium carbonate supplier to avoid?

A COA that only repeats the TDS with no lot number or date; a whiteness figure quoted with no method; a COA that lists D50 only and hides the D97; iron not reported; and a supplier who says the COA will follow after the goods arrive. A per-lot COA exists the moment the lot leaves the plant — if a supplier cannot provide one before shipping, treat it as a red flag.