Choosing a materials testing laboratory, or comparing materials testing laboratories against each other, by the scope on the certificate rather than by a capability list: why an iso 17025 lab is accredited for named methods and not for competence in general, what a polymer testing laboratory and water testing laboratories each have to hold to sign a result you can rely on, where industrial testing equipment and industrial laboratory equipment bought in house beat sending materials lab testing out and where they plainly do not, what a thermal conductivity tester and similar single purpose instruments cost to keep calibrated, and what a quotation has to state before two laboratories can be compared

Selecting a laboratory

1. Read the accreditation scope, not the website. Accreditation bodies publish the exact methods each laboratory is accredited for. Check that your method appears, by standard number, rather than relying on a general claim of accreditation.
2. Name the method in the enquiry. Different standards for the same property give different numbers, and a laboratory quoting against an unnamed method will choose the cheapest. State the standard and the acceptance criteria in the request.
3. Ask what is subcontracted. Many laboratories subcontract part of a panel. That is acceptable when declared and disclosed on the report, and it affects turnaround, chain of custody and who is accountable for the result.
4. Establish sample requirements before shipping. Quantity, conditioning, packaging and how the sample must be identified. Samples rejected on arrival or conditioned incorrectly are the commonest cause of a delayed report.
5. Compare turnaround including reporting. Test time and report time are different, and the second is frequently longer. Ask for the quoted turnaround to be to a signed report, and ask what expediting actually costs.
6. Decide in house against outsourcing on volume and defensibility. Routine high volume testing with a stable method suits in house equipment. Occasional testing, unusual methods and anything requiring accreditation is almost always cheaper and safer outsourced.

Scope is the whole question

A certificate of accreditation is accompanied by a schedule listing the methods, materials and ranges it covers. That schedule is the useful document, and it is public. Reading it takes minutes and prevents the discovery that a report cannot be used.

Where your method is outside the scope, ask whether it can be added, what that costs and how long it takes. Sometimes it is straightforward; usually it is not worth waiting for.

Uncertainty is part of the result

A measurement without a stated uncertainty cannot be compared to a specification limit honestly, because a result near the limit may or may not exceed it. Accredited reports state it; unaccredited ones often do not.

Ask for it explicitly, and use it when setting internal limits. A specification tighter than the measurement uncertainty is a specification that will fail randomly.

Common questions

Does accreditation mean every test is accredited?

No. It applies to a defined scope of methods, and laboratories routinely perform unaccredited work alongside accredited work. The report should distinguish them, and you should check which yours is.

Why do two laboratories report different values?

Different standards, different specimen conditioning or different sample preparation, in that order. Naming the standard and the conditioning in the request removes most of the discrepancy.

When does in house equipment pay?

When the same test is run often enough that per sample outsourcing exceeds the cost of the instrument, calibration and the person. Single purpose instruments used occasionally are usually a poor investment, because calibration continues whether they are used or not.

What should a test report contain?

The method by its standard reference, the specimen description and conditioning, the equipment used, the result with its uncertainty, any deviations, and a signature. A number without those is not a report.

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