12. Contamination Diagnosis and Deposit Defects

First divide the problem

Before changing chemistry, classify the defect:

Preparation: poor cleaning, oxide, passive surface, smut.

Electrical: wrong current density, bad contact, poor anode geometry.

Mechanical: particles, rack movement, trapped gas, poor drainage.

Operating condition: temperature, pH, agitation, filtration outside target.

Contamination/chemistry: metallic impurities, organic contamination, decomposition products, additive imbalance.

Metallic contamination

Possible clues include dark low-current-density deposits, poor ductility, haze, streaking, or unusual Hull-cell patterns. Do not identify a specific contaminant from appearance alone. Confirm analytically where practical.

Organic contamination

Possible sources include oils, cleaners, polishing compounds, degraded additives, plasticizers, incompatible hoses, and accidental chemical carryover.

Particulate contamination

Particles commonly cause roughness, nodules, or isolated bumps. Filter and identify the source instead of only replacing filter media repeatedly.

Cross-contamination

Dedicated tanks, pumps, hoses, measuring tools, and labeled additive containers reduce accidental cross-contamination.

Quarantine rule

When an unknown chemical has entered a production bath, stop additions, document the event, isolate the bath if possible, and test before processing valuable parts.