Pinholes in tiles are tiny holes in the glaze surface, usually caused by gas escaping during firing or by glaze application faults. Chipped edges are small breaks along the tile edge, usually caused by handling, cutting or packing. Both are common, and the question is how many per box a standard lets through.
No single limit fits every order. Agree the acceptance rule in writing before production, and measure against it at inspection.
What causes pinholes?
Pinholes appear when something disturbs the glaze surface as it melts. Typical causes include:
- Gas escaping from the body or the glaze layer during firing, leaving a tiny crater.
- Glaze applied too thickly, too thinly or unevenly.
- Dust or contamination on the tile surface before glazing.
- Firing curves that do not suit the body and glaze combination.
Pinholes matter more on polished and glossy tiles, where light shows every flaw, and on large, plain colours. They are harder to see on textured or heavily printed surfaces.
What causes chipped edges?
Chips usually happen after firing. Common causes are rough handling on the line, poor edge finishing, weak cartons that let tiles knock together, and impact during transport. Rectified tiles have a cut, sharp edge that chips more easily than a pressed edge. See rectified against non-rectified tiles.
Chips on the face of a tile are a surface defect. Chips on the back or on an edge that will be hidden by grout are less serious, and your specification can say so.
What is reasonable to accept?
Tile standards deal with visible surface defects as a share of tiles. The ISO 10545 test method for surface quality expects most tiles in a lot to be free of visible defects when viewed under set conditions, and the exact threshold is set out in the standard. Check the current text of the standard your market uses.
For a purchase order, translate this into plain terms. State the grade, the viewing distance and light, and the maximum share of tiles with defects. Keep the factory's written grade definition, and see tile grades: Premium, Standard and Commercial.
How should inspection handle them?
Use a sampling plan so the decision does not depend on one inspector's opinion. AQL for tile inspection explains the method. Count defects in the sample against the agreed limit, and photograph every rejected tile.
Separate defects that come from production, such as pinholes, from defects caused by handling, such as chips. Production defects mean the grade is wrong, while handling defects point to packing and loading problems. Common floor tile defects shows others to look for.
How do you write the rule into the order?
Put the defect rule in the purchase contract. State the grade, the inspection method, the sample size and the number of defects allowed. Add a remedy, such as replacement or a credit, if the lot fails. A rule that everybody has read before production is far easier to apply than one argued about after the tiles have arrived.
Next step
We inspect against your agreed grade and sampling rule and record the result with photographs. To set acceptance limits for an order, book a free sourcing review.