What aspects should be considered when evenly coloring brass pull handles?

I. Substrate and Pre‑treatment (Most Critical)

1. Prioritize H59‑H62 brass with stable copper‑zinc composition to reduce inherent color difference.

2. Achieve consistent polishing and brushing; remove tool marks and burrs. Thoroughly eliminate polishing wax, oil contaminants and fingerprints.

3. A continuous unbroken water‑film after degreasing is required. Do not prolong mild‑acid activation to avoid over‑etching and mottling.

II. Process Control During Coloring

1.Temperature: Keep the solution or workpiece temperature stable within ±1‑2℃.

2.Workpiece status: Prevent workpieces from stacking or touching one another; avoid trapped air bubbles in grooves and holes.

3.Time: Apply identical coloring time for the whole batch.

4.Coloring solution: Maintain agitation and circulation, filter out impurities, and regularly adjust solution concentration.

III. Post‑treatment

1. Rinse sufficiently after coloring. Residual solution will lead to gradual discoloration.

2. Seal antique finishes with lacquer or wax protection.

IV. Common Causes of Color Defects

Fingerprints and oil stains, over‑pickling, temperature fluctuation, trapped air due to stacked parts, unstable material batches, and incomplete rinsing.