Scope of this guide
Junior version: what you will see, what you record, and what you never touch. Recognise early, escalate fast.
Series: finishing.com recurring questions answered with platingclub line practice. Parameters are industry-standard starting ranges — confirm against your supplier TDS.
Triage: symptom → confirm → first move
| Symptom | Likely root | Confirm by | First move |
|---|---|---|---|
| Film wipes off, powdery | Bath too hot / too long | Time-temperature log | Cut dwell; check heater |
| Iridescent patchy colors | Uneven zinc surface from rinse drag | Pre-chromate rinse check | Fix counter-flow rinse |
| Bare spots after chromate | Oil/silicone on zinc | Water-break test before chromate | Pre-clean audit |
| Weak color, fades fast | Bath exhausted / pH drift | Titration + pH | Rebalance per TDS |
| Color varies by rack row | Drag-in concentration gradient | Position sampling | Dip discipline; agitation |
Recognise, record, escalate
| You see | You do | You never do |
|---|---|---|
| Film rubs off | Log dwell time and temp | Re-chromate the same parts longer |
| Patchy colors | Check rinse tank condition first | Add chromate to 'strengthen' |
| Bare spots | Water-break test and report | Scrub parts in the tank |
| Any color dispute | Photograph next to the standard card | Argue from memory |
Engineer notes
- One variable per corrective action; verify with the confirm-by column.
- Records beat memory: log every trial on the tank card.
- Two failed actions in a row is a senior call — escalate with your log.
Safety: hexavalent chromate is a known carcinogen and sensitizer. Gloves, apron, face shield, exhaust on; trivalent lines preferred wherever spec allows.
FAQ
Why did the film rub off?
Soft film: too hot or too long in the chromate. Log the numbers before anything else.
What color should it be?
Whatever the customer standard card says — photograph against it, do not judge from memory.
Is chromate dangerous?
Hexavalent is; gloves, apron, shield, exhaust. Trivalent is the safer system where spec allows.