Chromite powder 200mesh/finer for coloring glass bottles
Chromite powder used for green coloring of glass bottles typically needs to be ground very finely. 200mesh and 325mesh chromite powders are commonly used for this purpose. For 200F chromite powder (≈74μm), particles larger than 100μm are strictly prohibited. This is not because they are impurities, but because coarse particles will cause incomplete melting, color spots, streaks, black spots, and color variations, severely affecting the appearance and quality.
I. Why Chromite Powder Cannot Contain Particles Larger Than 100 Micrometers
1. Incomplete Melting, Forming “Black Spots/Impurities”
Glass melting temperature is approximately 1400–1500℃. Chromite powder is mainly Cr₂O₃. While the surface of coarse particles >100μm may melt, the core remains unmelted, leaving small solid particles in the glass, forming black/dark green raised spots visible to the naked eye—a serious defect.
2. Uneven Dispersion, Causing Color Spots and Stripes
Coarse particles are difficult to disperse evenly and tend to accumulate locally:
– Areas with many particles → Dark green/blackish-green patches
– Areas with few particles → Light green/whitish
They can also form color stripes along the flow direction, resulting in uneven and mottled color throughout the bottle.
3. Affecting Glass Strength and Smoothness
Unmelted coarse particles are equivalent to hard internal impurities, causing stress concentration, reducing the strength of the glass bottle, and making it prone to bursting and cracking; the surface will also be rough due to the raised particles.
II. Relationship Between 100μm and 200 Mesh
– 200 mesh: Sieve opening ≈ 74μm, should ideally all particles pass through, with a particle size ≤ 74μm.
– >100μm (150 mesh): This is considered severely coarse particle, far exceeding the 200 mesh upper limit, posing an extremely high risk.
– The industry typically has stricter standards: high-end green bottles commonly use 200 mesh (≤75μm) and 325 mesh (≤45μm) to avoid black spots.
III. Will it produce impurities?
– Chromium ore powder itself is a coloring raw material, not an external impurity.
– However, >100μm coarse particles = process defects, manifesting as black spots, color patches, and color streaks, which appear as “impurities” in the finished product.
– True chemical impurities (such as Fe, Si) are another matter; coarse particles are a physical/process issue.
