A tiny dark point, an exposed patch and a network of fine lines may all be called a “glaze problem” in a hurried inspection. They are not the same condition. Sanitaryware glaze defects should first be described by visible morphology and location, then confirmed and traced. Jumping directly from appearance to a single firing or glaze cause can send corrective work in the wrong direction.
This guide gives buyers and factory teams a practical decision path: classify the observation, photograph it consistently, decide whether the lot needs containment, and investigate process evidence. Published ceramic research identifies pinholes, crawling and crazing as recurring sanitaryware glaze defects, but a photograph alone cannot prove the responsible process variable. For approved colour and sheen references, pair this process with the ceramic glaze and colour guide.
Key takeaways
- Name the morphology: Record point, crater, bare patch, line network or chip instead of using one generic defect label.
- Map the location: A defect on a hygienic contact surface, hidden rear face or fixing edge has different consequences.
- Contain before diagnosing: Hold affected batches and preserve samples before changing glaze, firing or repair practice.
Glaze-defect observation and disposition card
| Evidence | What to record |
|---|---|
| Visible morphology | Point, pit, bare patch, line network, chip or other neutral description |
| Location and extent | Fixture zone, scale, count or cluster, contact/functional relevance |
| Cause status | Observed fact separated from suspected factors and evidence still needed |
| Batch action | Hold, expanded inspection, sort, approved rework, replacement or rejection |
| Decision | Specification/sample used, reviewer, date and release record |
01 VISUAL LANGUAGE
What do pinholes, crawling and crazing look like?
Pinholes are small openings or pits that interrupt an otherwise continuous glaze. A blister is raised or domed; a crater is a larger opened depression. Crawling appears where glaze retracts and leaves an irregular bare or thinly covered area. Crazing is a network of fine cracks within the glaze surface, often easier to see under angled light.
Do not confuse these with impact chips, grinding marks, dirt, mould seams, glaze colour variation or a crack through the ceramic body. Clean the sample with an approved neutral method, inspect it dry under both diffuse and raking light, and record whether the feature can be felt. Do not use dye or destructive confirmation on saleable goods without approval.
02 DEFECT MAP
Why do defect location and density matter?
Mark each observation on a simple fixture drawing. Record bowl interior, rim, water-contact zone, visible exterior, rear face, underside and fixing area separately. Count defects within an agreed inspection zone and include a scale in close photographs. One isolated point and a cluster following a casting or spray path are different process signals.
Buyers should approve appearance limits before production, using physical boundary samples where possible. A generic phrase such as “no defects” creates disputes because inspection distance, lighting and critical surfaces are undefined. Functional, hygienic and visible zones can have different rejection rules, provided mandatory standards and customer requirements are met.
03 CONFIRMATION
How can QC confirm a suspected glaze defect?
Begin non-destructively: clean, dry, change the light angle, use magnification and compare with a signed reference. Photograph an overall view, a location view and a close view with scale. If a line crosses from glaze into the body, reaches an outlet or fixing point, or changes after controlled testing, escalate it as a possible structural issue rather than a cosmetic observation.
Laboratory or process teams may use microscopy, sectioning, thermal-expansion work or controlled refiring trials on retained samples. Those methods belong in a root-cause investigation, not on customer goods. The report should distinguish what inspectors observed from what engineers later inferred.
04 ROOT CAUSE
Can appearance identify the process cause?
Only partially. Pinholes can be associated with gas release, surface contamination, glaze rheology, application thickness, drying or firing conditions. Crawling can involve weak adhesion, dusty or overly dry surfaces, excessive shrinkage of the glaze layer or application conditions. Crazing concerns stress and fit between glaze and body, including thermal expansion and process history.
These are hypotheses, not verdicts. Check batch records for body and glaze preparation, density and viscosity controls, spray parameters, drying time, kiln loading and firing curve. Compare good and defective pieces from the same period. Change one controlled variable at a time and repeat enough pieces to show the effect is stable.
05 LOT CONTROL
What should happen when defects appear in a shipment lot?
Quarantine the affected batch and stop mixing suspect cartons with accepted stock. Trace mould, shift, glaze batch, kiln car and firing window where records permit. Inspect a defined sample from neighbouring batches and map the same zones. Preserve representative good and defective pieces before rework or disposal.
Agree the disposition in writing: accept to an approved limit, sort 100 percent, rework only through an approved process, downgrade, replace or reject. Cosmetic touch-up must not hide a structural crack, create a hygiene issue or invalidate certification. Re-inspect repaired pieces under the original method.
06 EVIDENCE
What should a supplier corrective-action report include?
A useful report contains defect definition, photographs, affected quantity, batch traceability, immediate containment, verified root cause, corrective action, preventive control, responsible owner and effectiveness check. “Worker was careless” is not a root cause unless the control system explains how the error occurred and why it escaped.
Buyers should ask what measurable process limit changed and how future lots will be monitored. The most persuasive evidence is a comparison of controlled production data and subsequent inspection results, not a polished presentation. Keep the report linked to purchase order, SKU and approved boundary sample.
07 BUYER INSPECTION
How should importers inspect glaze on arrival?
Use consistent illumination, viewing distance and fixture orientation. Clean dust before judgement and avoid touching suspect marks until photographed. Sample cartons across pallet positions and production identifiers rather than opening only the easiest top layer. Record packaging damage separately because impact can imitate or create ceramic defects.
If a serious line, exposed body area or dense cluster appears, pause installation and expand inspection under the contract plan. Share neutral evidence with the supplier: carton, batch, full fixture, exact location and close detail. This shortens diagnosis and prevents a single phone photo from becoming an argument about the entire shipment.
08 PURCHASE CONTROL
How should glaze quality be written into a purchase specification?
Define glaze colour and finish, critical surfaces, inspection lighting and distance, allowed boundary samples, sampling plan, defect terminology, disposition process and any applicable product standard. Require batch traceability sufficient to contain a problem. Do not copy a tolerance from another ceramic category without confirming it fits sanitaryware and the target market.
Chengda can review finish expectations and inspection records for ceramic sanitaryware orders. Final acceptance should follow the signed product specification, approved samples, destination requirements and the evidence from the actual lot.
FAQ COMMON QUESTIONS
Frequently asked questions
Are glaze pinholes only cosmetic?
Not automatically. Location, depth, density, hygiene implications and the applicable specification determine disposition.
Is crazing the same as a body crack?
No. Crazing is a fine crack network in glaze; a crack through the ceramic body is a different and potentially structural condition.
Can crawling be polished away?
An exposed or retracted glaze area should be assessed under the approved disposition process. Polishing is not a universal repair.
Can one photo prove the root cause?
No. A photo supports classification; root cause needs traceability, process records and controlled confirmation.