Separating iron oxide pigment lot variability from equipment dispersion effects

Trial design and interpretation

Prepare replicate color panels with the reference and candidate pigments, reverse the panel preparation order and record grinding conditions. If the color difference follows equipment run order rather than lot number, check dispersion and panel repeatability first.

Recording Oil absorption

Oil absorption (mL/100 g): ENVO published examples: red 15–25, yellow 25–35. Applies to the stated pigment class. Agree oil type, endpoint and specific colour grade at sample approval. Water-soluble salts (% by mass): ENVO published red, yellow grades ≤0.3. Use the specified colour grade and state the extraction conditions.

Why does a single red iron oxide lot give uneven colour?

Check substrate colour, water addition and curing separately. Prepare samples at the same pigment loading and layer thickness. Concrete coloration: Fix cement type, water-to-cement ratio and curing time. Measure dry color difference and keep a reference block.

What to record

• Pigment lot
• Grinding conditions
• Panel preparation order
• Instrumental color difference

Technical references

• ENVO · Iron Oxide Pigments catalogue and product information ↗

Products and processes