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D263-05 – Standard Test Method Technical Guide
🔬 Composition and Purity Limits
ASTM D263-05 (Reapproved 2023) specifies that Chrome Oxide Green Pigment must consist of practically pure chromium sesqui-oxide (Cr₂O₃) without any admixture of other materials. The following conformance requirements are mandatory under the standard.
| 🟦 Property | 📐 Specification Limit | ⚙️ Test Method |
|---|---|---|
| Total Chromium (as Cr₂O₃), min | 98.0 % | ASTM D126 |
| Total Matter Soluble in Water, max | 0.5 % | ASTM D126 |
| Moisture and Other Volatile Matter, max | 0.5 % | ASTM D280 |
| Coarse Particles (No. 325 / 45 µm sieve), max | 1.0 % | ASTM D185 |
| Organic Colors or Lakes | None | ASTM D126 |
✅ Conformance Note: The standard requires a minimum Cr₂O₃ content of 98%, a maximum of 0.5% water solubles and moisture, and strictly prohibits the addition of any organic colorants.
📏 Sampling Plan and Test Procedures
Section 4 of D263 provides a detailed sampling plan to ensure representative testing. Two random samples must be taken from different packages for each lot or production unit. For shipments, this equates to two samples per 4,545 kg (10,000 lb), with a minimum of two samples for any shipment smaller than this threshold. Purchasers may test samples individually or blend those from the same production unit into a composite sample for testing.
Testing must be performed strictly according to the referenced ASTM methods, as summarized in the table below.
| 📐 Required Analysis | 🎯 Referenced Standard | ⚡ Key Application |
|---|---|---|
| Chromium Content Analysis | ASTM D126 | Confirms Cr₂O₃ content (min 98%) |
| Water Solubles | ASTM D126 | Measures total soluble matter (max 0.5%) |
| Moisture and Volatiles | ASTM D280 | Determines volatile content (max 0.5%) |
| Coarse Particle Sieve Analysis | ASTM D185 | Residue on 45 µm sieve (max 1.0%) |
| Screening for Organic Colors & Lakes | ASTM D126 | Ensures no added organic colorants |
⚠️ Sampling Warning: When packages lack distinguishing production unit markings, samples must be taken from different packages in the ratio of two samples for each 10,000 lb (4,545 kg). Shipments under this weight still mandate a minimum of two random samples.
🎨 Tinting Strength and Color Agreement
Beyond chemical purity, Section 3.2 of D263 requires that the mass color, the character of the tint, and the tinting strength of the pigment fall within limits mutually agreed upon by the purchaser and the seller. This evaluation is performed by mixing the pigment with a white pigment and visually or instrumentally comparing it to an established standard acceptable to both parties.
💡 Best Practice: To avoid disputes, ensure that physical or spectrophotometric standards for both mass color and tinting strength are mutually approved and documented before production begins. The tinting strength and tint character must be within the agreed range of the reference standard.
❓ Frequently Asked Questions
🔍 What is the minimum purity required for Chrome Oxide Green under ASTM D263?
The standard mandates a minimum total chromium content, calculated as Cr₂O₃, of 98%. The pigment must be practically pure chromium sesqui-oxide without any admixture of other materials or organic lakes.
💡 Which ASTM methods are used to test total matter soluble in water?
Total matter soluble in water is tested in accordance with ASTM Test Methods D126. The permissible maximum limit for water solubles is 0.5%.
⚡ What is the maximum limit for coarse particles retained on a No. 325 sieve?
The maximum total residue retained on a No. 325 (45 µm) sieve is 1.0%. This test is conducted according to ASTM Test Methods D185.
📌 How should samples be taken if shipment packages lack production unit markings?
If no markings distinguish between units of production, samples must be taken from different packages in the ratio of two samples for each 4,545 kg (10,000 lb). For shipments of less than 10,000 lb, a minimum of two samples must be taken.