Summary: Check 8 lines on the COA before buying: MnO₂ content, Fe, SiO₂, LOI, heavy metals, moisture, particle size (D50/D90), and the test methods. Missing lines are red flags. Verify the batch number, date, and QC signature. Confirm with one independent lab test on your sample.
The Short Answer: 8 Lines on the COA Decide Whether the Product Works
The COA is the batch’s identity card. It records what was made, how it was tested, and what it contains. Check eight lines before you compare prices. The COA decides whether the product works in your melt.
Why the COA Is the First Quality Gate — Not the Last
The COA tells you what is in the bag. It is the first quality gate, not the last. It proves the lot, not the brochure. Use it to filter suppliers before sampling. Then verify with your own test. Buying without a COA is buying a promise. Glass color does not run on promises.
The 8 Lines at a Glance: Chemical, Physical, and Methods
| Group | Lines |
|---|---|
| Chemical | MnO₂, Fe/Fe₂O₃, SiO₂, LOI, heavy metals |
| Physical | Moisture, particle size (D50/D90) |
| Documentation | Test method, batch number, date, QC signature |
How to Read This Article with Any Supplier’s COA in Hand
Open the COA. Find each line as you read. Compare it with the reference values in this article. Mark the missing lines. The whole check takes five minutes.
The Chemical Lines: What the Assay Tells You
MnO₂ Content: The Headline Number (and What “as MnO₂” Means)
Glass-grade MnO₂ typically runs 88–92%. “As MnO₂” means all manganese is expressed as the MnO₂ molecule. It is a reporting basis, not a purity certificate. Low MnO₂ means more filler and a higher real dose. Correction: material needed = active MnO₂ ÷ grade. Example: 1000 kg of 92% grade delivers 920 kg of active MnO₂. The same weight at 88% delivers 880 kg. Dose on the active value, not the bag weight.
Fe / Fe₂O₃: The Color Protector
Iron causes the green color you are buying MnO₂ to remove. Iron inside the MnO₂ adds the defect instead of removing it. Glass-grade spec: Fe₂O₃ ≤ 0.20%. Ask whether the value is reported as Fe or Fe₂O₃. Compare all suppliers on the same basis. Fe enters from ore and from processing equipment. Two lots with the same MnO₂ number can differ in Fe.
SiO₂: The Impurity That Dilutes Performance
SiO₂ is inert in the melt at these levels. It dilutes the active MnO₂ and adds batch weight without function. Glass-grade spec: SiO₂ ≤ 2.0%. High SiO₂ usually signals low-grade ore. Check the SiO₂ trend across lots. A rising line usually tracks a cheaper ore source.
LOI: What It Says About Melt Behavior
LOI stands for loss on ignition. It measures volatiles, bound moisture, and organics that burn off in the melt. High LOI means more gas release in the furnace. Glass-grade spec: LOI ≤ 5.0%. High LOI risks bubbles and dosing loss.
Heavy Metals (Pb, Cd, Cr): The Compliance Gate for Sensitive Glass
Tableware, crystal, and food-contact glass must meet heavy metal limits. Ask for Pb, Cd, and Cr values on the COA. Limits follow your market’s regulations, such as EU and FDA rules. No data means no compliance proof. Ask for limit values, not just “pass”. Compare them with your product’s requirement before production.
The Physical Lines: What Processing Tells You
Moisture: The Dosing Accuracy Killer (Why ≤ 2.0% Matters)
Moisture adds weight that is not MnO₂. At 2% moisture, a 1000 kg lot carries 20 kg of water. Dosing errors shift the color. Moisture also causes clumping and segregation in the batch. Glass-grade spec: moisture ≤ 2.0%. Weigh the bags at arrival. The delivered moisture, not the COA number, is the real dose input.
Particle Size (D50/D90): The Performance Spec
Particle size controls dissolution speed and dispersion uniformity. A consistent D50/D90 is a performance spec, not a handling detail. D50 is the median; D90 describes the coarse tail. Require a range, not a single value. Related reading: What Particle Size of Manganese Dioxide Is Best for Glass? and How Does MnO₂ Particle Size Affect Glass Decolorization?
Test Methods: How to Trust the Numbers
Standard Test Methods to Expect for Each Line
| Line | Expected method |
|---|---|
| MnO₂ | Titration (oxalate or iodometric) |
| Fe, heavy metals | ICP-OES or AAS |
| SiO₂ | Gravimetric or ICP |
| Moisture | Gravimetric drying or Karl Fischer |
| LOI | Muffle furnace, about 950 °C |
| D50/D90 | Laser diffraction (ISO 13320) |
| Bulk density | Tapped or apparent density |
Same Numbers, Different Methods: Why Method Matters in Comparisons
Numbers are only comparable on the same method. Different labs, different instruments, different results. Ask which method and which instrument produced the data. Compare COAs on the same basis. Old test dates describe the past, not the shipment.
COA Red Flags and Verification Steps
Red Flags: Missing Lines, Wide Ranges, and “Typical” Wording
- Missing lines: gaps hide problems.
- Wide ranges: “MnO₂ 80–98%” is not a spec.
- “Typical” wording: typical is not guaranteed.
- Identical values across different lots: data may be copied.
- No batch number: the COA cannot be tied to the lot.
Ask the supplier to explain each missing line. The explanation is often more revealing than the line itself.
Check Batch Number, Date, and QC Signature
The COA must name the batch it describes. Match the batch number on the bags. Check the test date against the production date. Look for a QC signature or stamp. Unsigned data is not a COA.
Verify with an Independent Lab Test on Your Sample
A COA is the supplier’s word. An independent test is yours. Test the sample: MnO₂, Fe, moisture, D50/D90. Compare the results with the COA. Differences beyond tolerance end the discussion.
Reference: A Complete Glass-Grade COA at a Glance
MnO₂ 88–92% / Mn Total 55–63% / Fe ≤ 0.20% / SiO₂ ≤ 2.0%
| Parameter | Glass-grade reference |
|---|---|
| MnO₂ | 88–92% |
| Mn (total) | 55–63% |
| Fe₂O₃ | ≤ 0.20% |
| SiO₂ | ≤ 2.0% |
Moisture ≤ 2.0% / D50 Customizable / Bulk Density 0.8–1.2 / LOI ≤ 5.0%
| Parameter | Glass-grade reference |
|---|---|
| Moisture | ≤ 2.0% |
| Particle size D50 | Customizable |
| Bulk density | 0.8–1.2 g/cm³ |
| LOI | ≤ 5.0% |
Reference values are typical glass-grade ranges. Confirm the exact values on your supplier’s spec sheet.
Frequently Asked Questions
What If the COA Doesn’t Show Fe or Particle Size?
Ask for them. No Fe means no color control. No particle size means no dissolution control. If the supplier cannot provide the data, find another supplier.
Should I Test Every Batch or Only Samples?
Test every batch at minimum: MnO₂, Fe, moisture, D50/D90. Spot-check heavy metals and SiO₂ per contract. Full testing of every batch is expensive. Targeted testing is not.
Can I Ask for a COA Before Ordering Samples?
Yes. Always. A supplier that cannot share a COA for current production has nothing to sell. Request the latest COA with the sample, then verify independently.
Conclusion: A 5-Minute COA Check Protects Your Whole Batch
Key Takeaways: Eight Lines, One Decision
- Check MnO₂, Fe, SiO₂, LOI, heavy metals, moisture, D50/D90, and methods.
- Missing lines, wide ranges, and “typical” wording are red flags.
- Verify the batch number, date, and QC signature.
- Confirm with one independent lab test.
- A five-minute check protects a whole batch.
Request Our Latest COA and a Sample for Independent Testing
BTLnewmaterial provides glass-grade manganese dioxide with a complete COA: MnO₂ 88–92%, Fe₂O₃ ≤ 0.20%, moisture ≤ 2.0%, and D50/D90 for every lot. Request our latest COA and a sample. Test it in your lab or an independent lab. The COA and the test together decide the order.
I am Edward lee, founder of manganesesupply( btlnewmaterial) , with more than 15 years experience in manganese products R&D and international sales, I helped more than 50+ corporates and am devoted to providing solutions to clients business.
