Three conditions for a valid comparison
Before two numbers can be placed side by side, all three of these must match:
- Method. Ash by ASTM D1762 is not the same determination as ash by ISO 18122, which is not the same as an in-house gravimetric method. Different methods ash at different temperatures and can yield different residues.
- Reporting basis. A value reported dry and one reported as-received describe different quantities of the same material — see why the test basis matters.
- Units and conditions. Percentages are only comparable against the same denominator, and performance values (burn time, ignition time) are only comparable under the same test conditions.
Build the comparison table first
Rather than comparing prose, extract each supplier's claims into one table with the same rows: fixed carbon, ash, moisture, volatile matter, size/tolerance, and any performance claim. Add a column for method and one for basis. A row where those columns differ is a row you cannot yet compare — mark it rather than averaging the two numbers.
The compare view on this sub-site presents recorded values on a common field schema, but it can only align fields that the records actually state; it cannot correct a missing method or basis.
Normalise moisture before anything else
Moisture shifts every other as-received figure, so it is the first thing to normalise. A supplier reporting 5% moisture and 80% fixed carbon is not directly comparable with one reporting 10% moisture and 78% fixed carbon until both are expressed on the same basis. When in doubt, ask both suppliers to restate their proximate analysis on a dry basis.
Watch for the missing fields
A supplier who omits the method, the basis, the batch reference or the laboratory is not giving you a specification — they are giving you a headline. The value of a comparison is limited by its weakest documented field. Ask for the raw report, not a summary PDF, and confirm the laboratory is independent of the supplier.
Compare batches, not one sample
A single best sample proves little. Where possible, request the same parameter across three consecutive batches and compare the spread as well as the headline. A supplier who holds ash between 2.8% and 3.2% is more predictable than one who alternates between 2% and 6% — even if both quote "max 3%".