Glass Packaging Quality Inspection

Background reading: the glass bottle manufacturing process, from sand to finished bottle.

A pre-shipment inspection of glass bottles or jars is a sampling exercise under ISO 2859-1 (ANSI/ASQ Z1.4), General Inspection Level II. Critical defects are judged at AQL 0.25 to 0.4, major defects at AQL 1.0 to 1.5 and minor cosmetic defects at AQL 2.5 to 4.0. It protects you only when three things are written down beforehand: the sampling plan, a defect catalog with photographic limits, and a contract remedy for a lot that fails.

AQL levels to write into the purchase contract

AQL stands for acceptance quality limit. Defects are sorted into three classes by their consequence, and each class gets its own limit.

On small samples the critical limit works out to almost zero tolerance. Where the minor limit sits depends on the product's price point; cosmetics and spirits programmes at the top of the market tighten it to 1.5 or below on visible surfaces.

Whichever values you pick, state them in the purchase contract next to the remedy: sorting at the supplier's cost, rework, or rejection. A limit with no consequence attached cannot be enforced.

Sample sizes and acceptance numbers by lot size

The plan below is for common export lot sizes. Ac is the highest defect count at which the lot is still accepted; Re is the count at which it is rejected.

These figures are the ISO 2859-1 single sampling values at General Level II and normal severity. Use them for planning; the plan for an actual shipment is set in the project's quality agreement, and reduced or tightened severity follows your contract terms.

One detail of the standard explains the last column. At AQL 4.0 the standard table shows an arrow instead of a plan for samples of 500 and 800 pieces, and the arrow points to the plan above: draw 315, accept at 21, reject at 22. So a 50,000-piece order draws 500 bottles, passes with up to 3 critical defects at AQL 0.25 and up to 14 major defects at AQL 1.5, and is judged for minor defects on the 315-piece plan.

The numbers mean something only if the sample is random. The inspector should choose cartons by grid across pallets, cartons and production shifts, and should refuse any "inspection sample" that the plant has set aside in advance.

Defect catalog with photographic limits

A written catalog backed by photographs of limit samples lets the inspector apply your standard without debate. For export glass containers it is usually organised like this.

Critical defects

• Birdswings and spikes, which are filaments of glass projecting into the container
• Inclusions of foreign material
• Through-cracks anywhere on the ware
• Chips on the sealing surface
• Fins sharp enough to cut
• Contamination inside the container

Under a standard quality agreement, one critical defect found in the sample rejects the lot until it has been 100-percent sorted at the supplier's expense.

Major defects

• Leakers, meaning ware that fails the squeeze or vacuum test
• Neck finish dimensions outside the tolerance on the agreed drawing, which ends closure compatibility
• Vertical load or internal pressure failures against ISO 7458 test levels
• Thermal shock failure per ISO 7459 on hot-fill ware
• Capacity deviating by more than ±3 percent
• Annealing stress, measured per ASTM C148, above the agreed limit
• Decoration faults: print that lifts in the cross-hatch tape test, colour outside the approved limit panel, or registration drift greater than 0.5 mm

Minor defects

This class covers seeds and blisters under a counted size limit, faint mould marks, light scuffing below the label panel, and slight waviness that cannot be seen at arm's length. Each limit has to be measurable. An inspector can check "seed ≤1.5 mm, maximum 2 per bottle, none in the upper third", but cannot check "no visible defects".

Functional tests by end use

Visual sampling is one half of the plan. The other half is destructive testing on units pulled from the lot, chosen according to what the container will hold.

Laboratory migration testing is not repeated on every shipment. For food-contact programmes, the migration reports against EU 1935/2004 or FDA 21 CFR are produced on first articles and re-verified on a periodic schedule. At each shipment the inspector checks those reports as documents, alongside visual sampling, gauge checks and portable functional tests such as pressure, thermal shock and torque.

How much verification each bottle route needs

The more of the bottle that is specific to your brand, the more there is to verify.

Booking an SGS or BV inspection

A third-party inspection moves through three stages.

1. Booking. You send the inspector the purchase order, defect catalog, limit samples, packing specification and AQL plan. These become the working documents.
2. Inspection at the plant. It takes place once at least 80 percent of the goods are packed. The inspector verifies quantity, draws the random sample, runs visual and functional tests, checks packing and marking against the export specification, and photographs everything.
3. Report. It gives measured data, defect counts set against the acceptance numbers, and a verdict of pass, fail or rework.

Most weak inspections trace back to a thin booking. Given nothing but a purchase order, an inspector performs a generic container check. Given your catalog, limit samples and packing specification, the same inspector enforces your standard. We assemble these into a single inspection pack before the booking is sent, as part of our export support for glass bottle projects. The supplier-side controls that come before this stage are covered in our guide to auditing a glass bottle factory.

To arrange an inspection through us, send a request with:

• product type, capacity and neck finish standard, with a drawing if you have one;
• lot size per shipment and annual volume;
• end use (hot-fill, carbonated, spirits or cosmetic), which decides the functional tests;
• the food-contact market, EU 1935/2004 or FDA, which sets the scope of document verification.

Contract clauses that make inspection enforceable

Three clauses carry the weight.

• Quality agreement. The defect catalog, AQL plan and limit samples are annexed to the purchase order.
• Inspection clause. Goods leave only after a passed report, and the buyer has the right to appoint the inspector.
• Remedy clause. A failed lot is sorted or reworked before shipment at the supplier's cost, and the supplier also pays for re-inspection.

Payment terms belong in the same draft. The remedy has force when the balance stays unpaid until a passed report exists, so inspection and payment milestones should be written together. Our sourcing checklist for glass packaging places these steps in order with the audit, sampling and documentation work.

Frequently asked questions

What happens to the shipment date when a lot fails?

The supplier sorts or reworks the lot, and a re-inspection confirms the fix before anything ships. The shipment date and the consequences of any delay are governed by the purchase contract, which is one more reason to settle the remedy clause before production.

Does every shipment need laboratory testing?

No. Migration testing for food-contact compliance is done on first articles and repeated periodically. A shipment inspection reads those reports and adds on-site sampling and functional tests, so its effort is counted in inspector man-days, not laboratory work.

What does an inspection cost?

It is quoted per project. The drivers are lot size, the functional tests your end use requires, whether decoration has to be tested, and whether loading supervision is included.