A glass plant can trace a bottle only if four things connect: a mark made at forming, a production record behind that mark, shipping papers that carry the same batch code, and a procedure that turns a complaint into a short list of affected lots. The mould number embossed on the glass is the strongest of these because the tool casts it into every bottle it makes. The fastest test of the whole system is a backward trace on a carton you pick yourself, which takes about an hour when the records are real.
Four things the system must let you do
Nearly every supplier says it has traceability, and a direct question rarely produces a "no". Judge the claim by whether the records support four actions without delay or negotiation.
- Trace backward. Starting from one complained-about bottle or one shipping carton, name the production date, forming machine, mould and raw material lots. Most plants manage this, since it follows the ordinary paper flow from order to delivery.
- Trace forward. Starting from a known production event, for example a mould discovered chipped partway through a shift, list each customer, pallet and carton that took bottles from it. This is harder. It only works if the record was written when the event happened and the code stayed with the goods past the packing line.
- Give a bounded answer. The exposure should come down to a justified window, typically a single shift or furnace campaign. A supplier who says anything made in the last quarter might be affected has no working system.
- Reproduce the evidence. A complaint raised a year on against a retained carton or stored sample should lead to the same records, and the batch identity should be readable on the physical article, not only in a database.
If any one of the four fails, the rest is decoration.
Stock bottle or private mould changes how far a trace can go
Buyers tend to raise this too late. A stock bottle bought in bulk through a trader may come from more than one campaign and may have been decanted, mixed and repacked, so the original production identity can be gone before the goods arrive. It survives only where the trader keeps lots separate and is willing to document that.
A private mould works the other way. The mould number belongs to one buyer, so the mark on the glass discriminates far better. Where traceability is a hard requirement, settle the sourcing model with that in view; retrofitting it onto a supply chain never built to carry a code is very difficult. If the specification is still open, the glass bottle and jar collections are the place to start comparing stock shapes with custom tooling.
The marks on the glass and the batch code built on them
Container glass is formed by a set of tools: a body mould, a mould for the neck and finish, a plunger or blow head, and the forming machine that carries them. Each tool has an identity number engraved in the metal, so the number is reproduced on every article. The bottle leaves the mould already carrying its origin, with no ink and no label.
| Element | What it identifies | What it helps you bound |
|---|---|---|
| Mould number | One specific set of tooling; unique and stable | A fault that repeats only on bottles with that number is a tool fault, not a process fault |
| Machine number | The forming machine, each with its own gob weight, timing and cooling regime | A process problem, down to one line |
| Date element | Usually a day or shift code, not a full calendar date | The problem in time |
| Furnace identifier | The furnace, where a plant runs several or one furnace feeds several lines | A glass chemistry problem, which follows the furnace and not the mould |
The batch code is a commercial layer above these marks. It is the string the plant writes in its records and on shipping documents, and it is normally a composite of a date or shift designator, a line or machine reference, a mould family reference and sometimes a customer or article reference. Construction differs from plant to plant.
For that reason, ask for the legend: the written rule, often a one-page internal standard, that states what each position in the code means. Without a written legend there is no coding system, only a habit of putting numbers on cartons.
Two points matter in practice. The embossed mould number and the batch code are separate things, and you need to be able to walk from one to the other: a code on a carton is useful only if the production record resolves it to a mould, a machine and a date window. Also, the mark is a feature of the tool. It may sit low on the heel or on the base, and a worn tool leaves it faint. Agree position and legibility on the approved sample and put that agreement in writing, so a later dispute over an unreadable code is decided by a document.
What a mould number tells you about a defect
Mould numbers make a quality discussion finite. A fault seen across all moulds comes from process or material, and the fix belongs to the furnace, the gob or the forming schedule. A fault confined to one mould is tooling: pull the tool, dress or replace it, and inspect what it made. That is the gap between stopping a line and quarantining a defined quantity, and it is visible only when the mould number was logged at production.
| Defect seen | Usual origin |
|---|---|
| Vertical line or seam on the body | A body mould joint, or wear or damage at the parting line |
| Repeating mark or dimple | The mould surface: a chipped or scratched cavity, or a repair that was polished in |
| Distorted neck or out-of-round finish | Neck ring tooling |
| Weight varying between moulds on one machine | Uneven gob distribution across cavities, a machine and feeder matter |
| Localised inclusion or stone | Glass chemistry or raw material; it ignores mould boundaries |
The last row is the one to escalate differently. A defect that pays no attention to the mould number is a batch or furnace issue and should not be handled as a tooling fault.
One detail catches buyers out. A line runs several moulds at once, numbered within a set, and a plant that reports a problem "on a mould number" may mean a single cavity or the entire set. Ask which convention applies. A wrong assumption multiplies or divides the affected quantity by the cavity count, and that quantity is what a claim rests on.
The four record families and where the joins fail
Audits find problems at the joins between documents, not inside any single one. Four families of record should connect:
- Production record – links day, shift, machine and mould to a quantity made and a batch code.
- Inspection record – links the batch code to checks during and after production: the sampling plan, number inspected, defects found and what was done with non-conforming output.
- Material record – links the production window to incoming lots of raw materials and colourants, and to external components such as closures and liners.
- Shipping record – links the batch code to cartons, pallets, customer and invoice. This is normally the only family a buyer ever sees.
Typical breaks are predictable. The shipping paper shows an order number in place of a batch code, so a shipment traces to an order but not to a production window. Inspection is logged per day, so two batches made on the same day blur together. Material records sit with purchasing as an invoice archive, which lets the plant say which colourant lots it bought but not which bottles hold them. Most often of all, caps, liners and labels are traced separately or not traced, so the pack leads back to the glass but not to the closure that sealed it.
The standard to hold a supplier to is simple. For any carton, records alone should settle which machine, mould and date window made the bottles, which inspection records cover them, which raw material and component lots were in use, and which other customers received output from the same window. One working day is enough for a chain that functions. A plant that has to rebuild that answer from memory over a series of meetings will be found out at the worst moment.
Two neighbouring subjects sit outside the trace itself. Which declarations and test reports a market expects, and who may sign them, is covered in our guide to the food contact declaration for glass bottles. How a drawing is read and how incoming inspection is written is covered under tolerance standards for glass bottles; a batch code that cannot be tied to a measured result documents nothing.
How to audit traceability on the factory floor
Run a random backward trace, and choose the sample yourself. Take a finished carton from a packed pallet and read the batch code off its label. Ask the quality team to produce, from records, the production date, machine and mould, the inspection record for that output and the raw material lots in use. Then go to the warehouse or retained-sample shelf and check that a kept bottle from the same window bears a matching physical mark.
Because the visitor picks the carton, nothing can be staged beforehand. Work through the checks below in order.
| Check | Sampling on site | Records to ask for | Warning signs | Pass |
|---|---|---|---|---|
| Mould number on the glass | Three bottles from one carton plus three from another pallet in the same shipment; read each code yourself under a light with a lens | The approved sample with the agreed code position; the drawing or tooling list defining the mould numbers of the set | Code missing or illegible on part of the lot; unexplained differences in mould marks between cartons; staff insist on reading the code for you | Every sampled bottle is legible, the position agrees with the approved sample, and each number exists in the tooling list |
| Machine and shift | With your own random carton, ask which forming line and shift produced it, then walk to that line | The day's production plan and a daily record giving article, line, shift and quantity | An answer from memory that the paper contradicts; the named line is running something else; the shift pattern described disagrees with the roster | Line and shift are confirmed at the machine and the record agrees with the carton code |
| Date and batch window | Ask for the window, not the date, and how each end is bounded | A dated production record with a defined cut-off; the rule for issuing a new batch code | Codes change arbitrarily; one code covers several days; nobody can say why a code was closed | A defined period, a written rule for opening and closing codes, and a cut-off visible in the record |
| Raw material and colourant lots | State a production window and ask which incoming sand, cullet or colourant lots were running | Receiving records joined to production by date; lot identity filed with the supplier certificate | Purchase invoices only; lot numbers that cannot be tied to a window; pooled colourant lots with identity lost | Named incoming lots for each window, with a documented join and no reconstruction |
| Closure, liner and other component lots | Ask which closure and liner lot went on the sampled carton and request the component supplier's own lot number | Component receiving record, the lot number, and the declaration or test position naming the article supplied | Components treated as accessories without records; the lot number appears on the packing list but not in the quality file; "the closure is not our responsibility" | The applied lot is identified, held in the quality file, and joins to the same window as the glass |
| Inspection and test records | Ask for the sampled batch's record, then for a non-conformance from that period and how it was closed | Sampling plan, measured results, defect classification, disposition of rejects, calibration status of the instruments | One summary sheet per month; no failed results because only passes are listed; instruments uncalibrated or unnamed | Per-batch results, failures present and dispositioned, instruments with valid calibration |
| Shipping document linkage | From the invoice or packing list, ask which batch codes it covers and check them against the cartons | A packing list or shipping paper carrying batch codes; the picking record tying cartons to the window | Order number only; codes entered on papers before production ended; packing-list codes that differ from carton codes | Document codes equal carton codes and resolve to production records for that window |
Scoping an affected lot after a defect is found
Test this procedure before you need it. It runs in five steps.
- Classify the defect as tool-linked, process-linked or material-linked, since the class sets the search boundary. A mould-specific fault covers one tool's output from the last known good check until the tool came out. A process fault, such as distortion that tracks one forming machine after a gob weight change, covers that machine while the setting was in force. A material fault such as a stone covers the furnace and the incoming lots; ignore that and the search ends up too narrow and too wide at once.
- Turn the technical window into commercial exposure: the cartons, pallets, shipments and customers that received output from the period. This step fails most often, for a dull reason. Production data and shipping data sit in separate systems and get matched by hand. Protect yourself by making it a condition of supply that the batch code is printed on packing list and invoice, and verify it once at audit.
- Decide a disposition for each group: hold and inspect, sort and rework, ship under a documented concession that the customer has agreed in writing, or scrap. Record the decision and its criteria per group so it can be reviewed afterwards.
- Notify with batch codes and quantities. A general statement obliges the customer to quarantine everything, which throws away what the system was built to deliver.
- Correct the system. Identify what was recorded late, what was joined by hand and which code was absent. If the close-out changes nothing in the record-keeping, the next campaign repeats the failure.
What FDA and EU rules ask of packaging traceability
Retailer questionnaires often cite a rule, so it helps to be exact about what the rules contain. In the United States, the general food safety framework stresses identifying the immediate supplier and immediate recipient of a food, and keeping records showing that a food contact material suits its use. The food contact provisions for packaging focus on whether a material is cleared and performs as intended. Traceability comes in as the practical means for a brand to react if a material proves unsuitable.
In the European Union, the food contact materials framework requires manufacture under good manufacturing practice, and the good manufacturing practice measure names traceability as an explicit element of a working quality system. A business is expected to identify who supplied it and whom it supplied, and to give that information to the competent authorities when asked. The plastics measure adds, for plastic layers, documentation linkable to the specific material and article.
Both regimes ask for a systemic capability and stop there. The record types and code formats that actually get checked come from the buyer's supplier manual and the customer's onboarding requirements.
Those requirements have grown more granular, pushed by retailers and not by any single new rule. A code that resolves only to a month increasingly falls short when a customer wants a shift-level answer. Agree the required resolution, meaning the level of detail the code must resolve to, with the first order and write it into the specification.
What to send us when setting a traceability requirement
We write traceability requirements and audit sequences for a specific project, and two inputs are enough to begin. One is the product line: bottle shape, closure format, and whether the article is a stock shape or a private mould. The other is the destination market, because brand-owner and retailer expectations, and the record-keeping they imply, vary between markets.
From those we can set out the code resolution your specification should demand, the records that should exist for one shipment, and the sampling sequence for a site visit. If a defect or complaint is already open, add what is known and the batch code on the affected carton so the scoping steps are applied to the real case.
Frequently asked questions
How does a mould number differ from a batch code?
The mould number is physical. The forming tool casts it into the glass, so it names that tooling and stays on the bottle for good. The batch code is a reference the plant writes on records and cartons, usually combining a date or shift, a line or machine and sometimes a mould family. The two must be linked through production records in both directions.
Which records should exist for a single shipment?
Five: production (window, machine, mould), inspection (measurements and their disposition), material (incoming raw material and colourant lots), component (closures and liners) and shipping (batch codes against cartons, pallets and customer). Their existence matters less than the joins. Correct records that cannot be tied to one production window answer nothing.
What exposes a system that exists only on paper?
Ask something the paperwork cannot answer without the goods. Have a retained bottle from a named window fetched and its mould mark read in front of you, or ask to see a non-conformance from that period and its closure. Paper-only systems tend to show monthly summaries, passes without any failures and order numbers where batch codes belong, and the answers turn vague once the conversation leaves the desk for the warehouse shelf.
Do FDA or EU rules prescribe a code format for the bottle?
No. Neither sets a format for glass packaging. Whether the code must resolve to a month, a day or a shift is fixed by the customer's supplier requirements, which is why the resolution belongs in the specification from the first order.
Can traceability be added later to a stock bottle supply?
Only in part. Identity may already be diluted by repacking across campaigns unless the trader has preserved lot separation and will document it. Plan for it at the outset and state the code resolution you need, so the limit does not surface during an audit.