Scope of this guide
Junior version: what you will see, what you record, and what you never touch. Recognise early, escalate fast.
This series answers a top recurring question from finishing forums with platingclub line practice. Parameters are industry-standard starting ranges — confirm against your supplier TDS.
Triage: symptom → confirm → first move
| Blister pattern | Likely root | Confirm by | First move |
|---|---|---|---|
| After plating bake only | Sub-surface porosity out-gassing | 200 °C re-bake test | Quarantine casting lot |
| Random single blisters | Oil or wax under deposit | Blister cross-section | Pre-clean audit |
| Edges and thin walls | Over-etch or acid dwell | Etch weight loss check | Cut acid time, verify strike |
| On flat faces in rows | Air trapped by rack angle | Position map | Re-rack angle 10–20° |
| Whole lot, every load | Casting gas content | Density / lot tag audit | Push back to foundry |
Recognise, record, escalate
| You see | You do | You never do |
|---|---|---|
| Blister after bake | Photograph, tag lot, call senior | Press the blister flat |
| Single blister mid-face | Note position, check pre-clean | Re-plate without cleaning |
| Edge blisters | Record acid station time | Extend acid to 'clean' more |
| Blister shows casting metal | Quarantine the lot | Blame the plating bath |
Engineer notes
- One variable per corrective action; verify by the confirm-by column.
- Records beat memory: log every trial on the tank card.
- Escalate when two consecutive actions fail — that is a senior call.
Safety: bake ovens hold hot parts and hydrogen risk from pickled parts is real. Heat gloves, face shield at door, and never load pickled zinc straight into a hot oven.
FAQ
Why do blisters appear only after baking?
Heat expands trapped gas from casting porosity under the deposit. The blister was born in the metal, not the bath.
Can I plate over a blister after popping it?
No — the void stays. Quarantine and report the lot.
What do I record for a blister?
Lot tag, position on rack, size and photo. The pattern identifies the cause.