How to Write a Chrome Oxide Green Procurement Specification
The difference between a good pigment supplier and a problem is usually written in the purchase order. Here is the clause-by-clause spec that makes quality enforceable.
The pain
Vague orders produce vague deliveries: "green pigment, as before" arrives as a different grade with a different D50 and a different compliance story.
The win
Nine clauses. Write them once, use them forever — and every incoming batch has a number to be judged against.
Clause 1 — Grade and identification
Name the exact grade (e.g. DELIKECOLORS GREEN 1025 or DELIKEOXIDE G-5001), CAS 1308-38-9, C.I. Pigment Green 17 (77288), and the supplier's internal code if any. No "or equivalent" without written approval.
Clause 2 — Chemical specification
Cr₂O₃ ≥ 99.0 % (ISO 4621; ≥ 98.5 % for sub-micron G-5070 / G-5073); water-soluble salts ≤ 0.70 %; Cr(VI) ≤ 10 ppm (or ≤ 5 ppm for low-Cr(VI) grades); screenings ≤ 0.30 % on 0.045 mm.
Clause 3 — Physical specification
D50 1.0–2.0 μm (micronized ≤ 0.5 μm; refractory grades per the G-series D50 windows); pH 6–8; oil absorption ≤ 25 g/100 g (ISO 787-5).
Clause 4 — Colour acceptance
ΔE ≤ 1.0 against the agreed reference in 1:10 TiO₂ tint, measured D65/10°. The reference chip is retained by both parties; any dispute is settled against it.
Clause 5 — Documentation
Every shipment carries a certificate of analysis with lot number, production date, test values and test standards. SDS (REACH Annex II / GHS format) and REACH registration statement accompany the first shipment and are re-issued on change.
Clause 6 — Traceability
Lot numbers trace to production records and raw-material batches. Blockchain/QR traceability where offered (VerdeChrome publishes QR per lot).
Clause 7 — Compliance
REACH Annex XVII, EU RoHS, China GB 18666 compliance confirmed per lot; California Prop 65 disclosure where applicable. Change of any compliance status requires 30-day written notice.
Clause 8 — Packaging and shelf life
25 kg paper bags on 1 t pallets, or 500/1000 kg big bags; product shelf life 10 years; dry storage; lot-separated loading.
Clause 9 — Rejection and audit rights
Inspection within 30 days of receipt; non-conforming lots are replaced or credited with return freight on the supplier; buyer reserves the right to audit the production site once per year.
The verdict
A specification this specific filters suppliers before the first shipment. Those who accept it without negotiation are usually the ones worth keeping.
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Specification template: the nine lines that matter
| Clause | What to write | Why it protects you |
|---|---|---|
| 1. Cr₂O₃ content | ≥ 99 % (or 98.5 % where specified) | Purity floor |
| 2. Colour ΔE | ≤ 1.0 vs. agreed master, CIE Lab | Batch consistency |
| 3. Tinting strength | 95–105 % vs. standard | Cost-in-use protection |
| 4. Cr(VI) | ≤ 5 ppm (Low-Cr(VI) tier) | Regulatory risk transfer |
| 5. D50 | Window, not single point (e.g. 1.2–2 μm) | Process fit |
| 6. Water-soluble salts | ≤ 0.70 % | Coating defect prevention |
| 7. Sieve residue | ≤ 0.1 % (45 μm) | Coarse-particle insurance |
| 8. pH | 6–8 | Formulation stability |
| 9. CoA per lot | Mandatory, traceable | Audit-proof supply chain |
A procurement specification is a pre-negotiation — it decides the outcome before the price is discussed. The single most common weakness we see is the specification written as a wish list instead of a control document: no test methods named, no frequencies set, no consequence for drift. A spec without a test method is a promise; with ISO methods named, it is a contract. The second weakness is over-tightening the wrong lines — demanding purity to three decimals while leaving Cr(VI) and D50 as “controlled”. Buyers who fix those two habits find that price discussions get shorter, because the supplier knows exactly what will be measured at goods-in. That is the quiet power of a well-written spec: it negotiates for you.
Why most specifications fail before they are issued
Specifications fail in three classic ways, and all three are visible in the document before the first shipment. The first is vagueness by design — words like “high quality”, “controlled” and “standard grade” appear where numbers and test methods should be. A specification written with adjectives is a wish; one written with methods is a contract. The second is missing consequence — the document lists limits but says nothing about what happens when a limit is missed: no re-test rule, no penalty, no rejection path. A limit without a consequence is a suggestion. The third is copy-and-paste procurement — the specification was inherited from a different supplier, a different application or a different decade, and no one alive knows why half the clauses exist. Specifications are living documents; one that has not been re-read this year is already out of date.
The anatomy of a professional specification
| Section | What it must contain | Common omission |
|---|---|---|
| 1. Scope & grade | Named product line, grades permitted | No grade fallback defined |
| 2. Chemical limits | Cr₂O₃, Cr(VI), salts — with methods | Limits without test methods |
| 3. Physical limits | D50 window, sieve residue, tinting strength | D50 as a single point |
| 4. Colour | ΔE vs. named master, CIE Lab | No master sample identity |
| 5. Sampling & testing | ISO 15528 sampling, test frequency, referee lab | No dispute path |
| 6. Documentation | CoA per lot, SDS currency, REACH statements | No document retention rules |
| 7. Consequences | Re-test rules, rejection, chargebacks | Entirely absent — the usual case |
Section 7 is where most specifications quietly collapse. A document that says “the supplier shall meet these limits” without saying what happens when they are missed is not a specification — it is an expression of optimism. The professional version defines the re-test right (who re-samples, who pays the referee), the rejection window (when a non-conforming lot becomes the supplier's problem, not the warehouse's), and the remedy (replacement, rework credit, or return freight). These clauses are never exercised in a healthy relationship — their value is that both parties know exactly what would happen, which keeps the relationship healthy.
Writing the Cr(VI) clause
The Cr(VI) line deserves special drafting care, because it carries the regulatory risk of the entire purchase. The weak version reads “Cr(VI) controlled” — two words that transfer nothing and protect no one. The professional version reads something like: “Water-soluble Cr(VI) ≤ 5 mg/kg, determined by diphenylcarbazide spectrophotometry per ISO 2080, on every lot, reported on the CoA; any lot exceeding 20 mg/kg is rejectable at supplier's cost.” Note what this clause does: it names the method, sets the frequency, attaches the reporting, defines the reject threshold, and allocates the cost. Every element protects the buyer from a different failure — the method protects against unverifiable claims, the frequency against cherry-picked lots, the reporting against silent drift, and the threshold against regulatory exposure. The same drafting discipline applies to every line; the Cr(VI) line simply has the highest stakes.
From specification to supplier scorecard
A specification becomes a management tool when its data is charted. The buyer who records every CoA into a spreadsheet owns a supplier scorecard within a year: ΔE and D50 means and ranges, salt levels, delivery reliability, and — critically — the trend lines. The scorecard does two jobs. It converts the annual supplier review from opinion to arithmetic, and it gives the buyer early warning: a supplier drifting toward the spec edge shows up on the chart six months before the first rejection. The scorecard also disciplines the buyer's own organisation — once the data exists, no one can quietly substitute an unapproved grade or accept a borderline lot on a Friday afternoon. The specification is the contract; the scorecard is the enforcement; together they are the difference between buying powder and buying reliability.
Specification templates for the three buying modes
- Pigment-grade buying (coatings, plastics, ceramics): the full nine-line table above — colour and D50 dominate, Cr(VI) ≤ 10 ppm as the regulatory floor.
- Refractory-grade buying (bricks, castables, kiln furniture): Cr₂O₃ content, D50 window by forming method, and the Low-Cr(VI) tier (≤ 5 ppm) where the plant is regulated — the specification is written around the kiln, not the colour.
- Functional-grade buying (catalysts, electronic ceramics, sputtering): purity to ppm level (Na, Fe, Ca, Mg, magnetic impurities), BET surface area, phase purity — colour is irrelevant and should not even appear as a clause.
A specification is the buyer's most under-used asset. Most organisations spend days negotiating price and minutes writing the specification — which is exactly backwards, because the specification controls the price's meaning and the supplier's behaviour for the whole year. The buyer who writes a methods-named, consequence-bearing, charted specification has effectively pre-negotiated every future dispute: when a lot arrives off-spec, both sides already know the procedure, the threshold and the cost. That is not paperwork — it is leverage, and it is the cheapest leverage in industrial buying. Our certificates and histories exist to slot directly into that machinery, because a supplier whose data fits a good specification never has to argue with it.
The spec review ritual
Professional procurement organisations review every active specification once a year, whether or not anything changed — because the world changes around the document even when the document stands still. The annual review asks five questions. Is the product line current? Grades are added and retired; a specification naming a grade the supplier no longer makes is an invitation to substitution. Are the methods current? ISO and DIN standards are revised on cycles; a method referenced by an obsolete edition invites dispute. Are the limits still tight enough? Regulatory floors have moved — the Cr(VI) ceiling that was market-leading five years ago is table stakes now. Are the consequences still credible? A rejection clause that no one would ever invoke is worse than none; it teaches the supplier the document is decorative. Does the scorecard data suggest tightening? A supplier running well inside spec for years is carrying capacity you are not using — or a spec so loose it tests nothing. The review hour, once a year, keeps the specification honest, and an honest specification is the buyer's cheapest form of authority.
What a good supplier wants from your specification
The best suppliers do not fear tight specifications — they fear ambiguous ones. A supplier reading a well-written spec sees exactly what will be measured at goods-in, what limits apply, what the re-test path is and what a failure costs; that clarity lets them price the risk honestly and run their process to match. A supplier reading a vague spec prices the ambiguity — into every quote, every lot and every silence. The asymmetry is worth stating: a precise specification costs the buyer an afternoon of writing and saves a year of arguing; a vague one saves the afternoon and costs the year. The suppliers who push back hardest against precise, methods-named specifications are usually not protecting their margins — they are protecting their freedom to drift. The buyer should read that resistance as information, and shop accordingly.
The specification is the only document in procurement that is simultaneously a contract, a measuring instrument and a negotiation strategy — and most buyers use it as a form. The difference between a form-filler and a professional is the scorecard: the professional charts the CoA data, reviews the document annually, and lets the numbers decide which clauses to tighten. In that discipline, the supplier becomes a partner measured by arithmetic rather than an opponent managed by relationships. We prefer buyers like that, because their specifications are where our process control is worth money — and a market where control is worth money is a market worth serving well.