Leather Test Report: What It Proves About Your Batch
A tannery can hand you three documents: a certificate, a data sheet and a test report. Only the third talks about the leather arriving at your factory, and only if it carries the right fields.
A guide by TL San Martín, a tannery of origin in Elda (Alicante, Spain) since 1995, LWG Gold certified under the Leather Manufacturer standard.
A leather test report proves something about your batch only when it identifies that batch: the tannery's batch number, article and colour, who took the sample, where on the hide it was cut and which method was used. Without that link, the report tells the truth about a piece of leather, but not about your order.
Certificate, data sheet, test report: what is the difference?
Each document speaks about a different level. Mixing them up is the most common way a brand ends up believing it holds a guarantee it does not have.
| Document | Covers | Question it answers |
|---|---|---|
| LWG certificate | The plant (the site) | Did this facility pass an environmental audit, under which standard, with which medal? |
| Technical data sheet | The article | What is this leather, and what does it normally measure? |
| Test report | A sample, ideally from your batch | Did the leather you received pass, measured by a laboratory? |
The certificate does not change with your order: it belongs to the site, and reading it is covered in how to read an LWG certificate. The data sheet describes the article "on average"; which of its lines actually bind the supplier is in leather technical data sheet. The test report is the only one that can speak about your batch: the leather tanned, dyed and finished together, with one colour result.
Which fields make a report valid for your order?
The laboratory competence standard, ISO/IEC 17025, already sets a minimum in clause 7.8: a unique report ID, the lab's name and address, the method used, a description and identification of the item tested, and the dates of receipt and testing. Most reports also carry one sentence worth reading slowly: the results relate only to the items tested.
That sentence is the whole point. The lab vouches for the piece of leather it received. The link between that piece and your order has to be written into the report, and it is the brand that must ask for it:
- The tannery's batch number, plus article and colour reference, matching the delivery note.
- Who took the sample. "Sample supplied by the client" means the lab does not know where it came from.
- Sampling position to ISO 2418. Thickness and strength change between the butt (the central back area) and the flanks; the standard fixes where the specimen is cut.
- Conditioning to ISO 2419 before physical tests. Without it, tear or flex values are not comparable.
- Accreditation with scope. A logo is not enough: check that the specific test is within the lab's accredited scope (UKAS in the UK, ENAC in Spain, DAkkS in Germany, or the national body where the lab sits).
- Limit of quantification for every chemical result. "Not detected" without a stated limit cannot be compared with a legal limit.
Which tests to ask for, and against which limits?
Some tests have a legal limit in the EU; others have whatever limit the brand writes into its spec. Keep them apart.
| Test | Method | Limit | Where the limit comes from |
|---|---|---|---|
| Chromium VI | EN ISO 17075 | 3 mg/kg | Legal: REACH Annex XVII, entry 47 (leather in contact with skin) |
| Aromatic amines from azo dyes | EN ISO 17234-1 | 30 mg/kg per amine | Legal: REACH Annex XVII, entry 43 |
| Thickness | EN ISO 2589 | Range in mm by zone | Brand spec |
| Rub fastness | ISO 11640 | Minimum grade, dry and wet | Brand spec |
| Tear load | ISO 3377-2 | Minimum force in N | Brand spec |
| Flex resistance | ISO 5402-1 | Cycles without cracking | Brand spec |
The legal chemicals carry the most weight. Chromium VI is not the chromium used in tanning: it forms when chromium III oxidises, so it is worth testing per batch in articles that touch skin, such as linings and insoles. If your range is chrome-free, the test still makes sense as a check; chrome-free leather for shoe brands explains what to ask for in writing.
Physical results depend on the product. A shoe upper does not have the same minimums as a bag leather, and the lab only measures: it does not decide whether a result is good enough for you.
When is a test report not good enough?
Six red flags, most serious first:
- No batch number, or one that does not match the delivery note.
- A different article or colour. Dyeing and finishing change the chemistry; a black proves nothing about a beige.
- Dated before your batch was produced. A report from two years ago is about the article, not the batch.
- An in-house lab without accreditation for that method. Fine for process control; not enough as proof to a customer or an authority.
- "Pass" with no values. Ask for the measured number and the limit of quantification.
- Leather tests mixed with footwear tests. A sole-to-upper bond test is about the finished shoe, not the leather.
A supplier holding only generic reports is not necessarily acting in bad faith: many intermediaries never see the batch. It is one of the practical differences covered in tannery vs leather distributor. If you are visiting the plant, ask to follow one batch from drum to label, as set out in the tannery visit checklist.
How do you write it into the purchase order?
Make the report a delivery condition, not a favour. Three lines are enough:
- Which tests, per batch or per season. For example: chromium VI per batch; physical tests per article and season.
- Who samples and who pays. Sample taken from the batch by the tannery and identified, or collected by your own lab.
- What happens on a fail. Batch held until retested, or replaced.
Add these to the questions to ask before a first order and you have the full chain: plant, article, batch. If you are launching a footwear brand and this is your first leather purchase, start from leather for shoes: what to buy first.
TL San Martín tans and finishes leather in Elda (Alicante) since 1995, certified LWG Gold under the Leather Manufacturer standard: the only LWG standard in which the Gold medal exists; a Trader can reach "Approved" at most. The certificate covers the plant; the test report covers your batch. You need both.
Disclaimer. The legal limits quoted come from Regulation (EC) No 1907/2006 (REACH), Annex XVII, entries 43 and 47, in the consolidated version published on EUR-Lex. This guide is not legal advice: TL San Martín is a tannery, not a compliance consultant. Confirm the requirements that apply to your product and market on EUR-Lex (or GOV.UK for UK REACH) and with your laboratory.
If you need a lab, a quality technician or a second opinion on a report you have received, ask on the Business Board, the open, free B2B board for the leather and footwear trade.
Post on the Business Board. Use Materials to describe the article (species, thickness, tests, quantity) or Freelance & services to find an accredited lab or a quality technician. Or request samples and tell us which tests you need.
Frequently asked questions
Does an LWG certificate replace a test report?
No. LWG audits the environmental performance of the plant. It does not measure chromium VI or the strength of the leather delivered to you. The two documents complement each other.
How often should I ask for a test report?
For chemicals with a legal limit in leather that touches skin, per batch is the safest basis. For physical tests, per article and season is usually enough, as long as the recipe does not change.
Is a tannery's report as good as one from my own lab?
It is if the lab is accredited for that test and the sample is identified with your batch. If not, treat it as process control and run your own independent check on a sampling basis.
What does "below the limit of quantification" mean?
That the method cannot measure below that value. For chromium VI, the limit of quantification must be below 3 mg/kg; otherwise the result does not show compliance.
TL San Martín tans and finishes leather in Elda, Alicante, since 1995: LWG Gold under the Leather Manufacturer standard — the only standard under which a Gold medal exists at all; a Trader tops out at “Approved”. Request samples before you specify anything.