Lead and cadmium rarely come from the sand, soda ash and limestone that make up soda-lime container glass. They reach a pack through four other routes: the colorant and refining agents in the batch, the recycled cullet fed into the melt, any decoration applied after forming, and the closure liner. Testing therefore has to follow the exact specification you are buying, on a sample from the production lot that will ship, and it has to distinguish what is in the material from what can migrate out of it.
The wider food contact dossier sits on a separate page about what a glass bottle food contact declaration must contain, and the test conditions and corrective route after an over-limit result are covered under migration testing and corrective actions for glass bottles. Nothing below is a claim of a certificate or a test result for any particular bottle.
Five points to settle before shortlisting a supplier
A bottle that looks bright and clean tells you nothing about its heavy metal content. You cannot see the risk or feel it, so it has to be handled when a supplier is qualified, not when goods are inspected. Five answers are needed before a first order.
- Destination market. The limit framework, the test conditions and the paperwork a retailer will accept are set by where the pack is sold, not by what goes in it.
- Glass type and colour. Clear, amber and green glass differ in risk, and a heavily coloured or opal container differs again.
- Decoration. A sprayed coating, an organic ink or a metallic lustre is an extra layer of material that the bare glass does not have.
- Batch knowledge. A plant that buys cullet and colourant from sources it cannot name has no basis for a heavy metal statement, whatever paper it issues. This is the point that most clearly divides a capable glass plant from a trading intermediary.
- Liability and hold point. Agree who pays if a lot fails and at which stage material is held before release.
Buyers who close these points early spend much less time on chemistry than those who start after a consignment has been stopped at a port.
Be realistic about what can be said at enquiry stage. A plant can describe its recipe family, its colouring route, the cullet share it runs and the reports it holds for current production. It cannot honestly promise an elemental result for a bottle that does not exist yet, because that result depends on the batch melted on the day. Ask for the specification and the historical evidence, then verify the acceptance limit on the first production lot instead of accepting it as a line on a quotation.
The four routes by which heavy metals enter a container
Each route has a different owner and a different corrective action, so keep them apart when you assess a pack. The word "glass" alone says very little about what a given container is made of.
Colorant and refining agents
Iron, chromium, manganese, copper and cobalt produce amber, green, blue and other shades, and some older colouring systems used elements that are now restricted. Refining and decolourising agents are added to the batch as well. Dark amber and dark green need a higher colorant loading than pale tints, so a saturated container carries a higher theoretical loading than a water-white one.
Recycled cullet
Cullet is recycled glass returned to the melt. It saves energy and steadies the melting process, and in most markets it forms a substantial part of a container batch. The exposure lies in where it comes from. Post-consumer streams can include bits of old leaded tableware, crystal, television panel glass, sealed-beam units and ceramic or earthenware with lead glaze, and these are not always sorted out before crushing. A high cullet share with no controlled supply and no incoming check means an unknown variable in every batch.
Decoration after forming
Organic inks, ceramic or glass enamels fired onto the surface, metallic lustre and some sprayed coatings can contain lead, cadmium or other restricted elements in their pigments, driers and metallic components. This route is easily missed: the plain body passes, the decorated bottle fails, and the whole difference lies in a step the glass plant may have subcontracted. Name the ink or enamel system in the decoration specification and ask for a compliance statement for it that is separate from the one for the glass.
Closure and accessories
Liners, gaskets, plastisol, foil seals, dropper bulbs and pump parts are not glass, yet they touch the product and fall under food contact rules of their own. A pack can fail on its liner while the glass is fully compliant. If the only document you ever requested came from the glass plant, you will have nobody to pursue for that finding.
How colour and glass system change the risk
Colour choice is also a chemistry choice. The scale runs roughly as follows.
- Clear flint with a little decolouriser sits at the low end.
- Light green and pale amber add a modest colorant loading.
- Deep amber, deep emerald and cobalt add more.
- Black glass and opal white are normally at the top, because depth and opacity come from higher additions or from a different glass system altogether.
If the brand wants a very dark bottle, ask which colouring system the plant proposes, not just whether the shade can be matched.
Lead-bearing glass, found in some crystal and heavy-base decorative ware, belongs to another category and cannot stand in for soda-lime packaging glass in food contact use. Where a market limits such glass to non-food use, the item has to be specified and marked accordingly, and it must never replace a food contact container on a line without a new compliance review. For a heavyweight, high-clarity base on a spirits bottle, find out early whether the proposed glass is soda-lime or lead-bearing. That answer alters the test package, the labelling and possibly the market you can sell into.
Decoration near the mouth and third-party decorators
Decoration is the route buyers underestimate most often. A fired enamel, a hot stamping foil, a lustre band or an all-over sprayed colour brings in a new material with pigment chemistry of its own. Two working rules follow from that.
First, anything applied on or close to the mouth, or at any point the liquid can reach while pouring, counts as food contact, not as decoration. Second, pigment compliance data normally sits with the decoration supplier, so the request for documents has to travel down the chain past the bottle maker. When a third party decorates the bottle, obtain that party's own declaration and file it with the bottle documents. A retailer's auditor will ask for it by name.
Composition tests and migration tests answer different questions
Most unusable reports come from mixing up two levels of verification. A composition test measures which elements are present in the glass, the colorant and the decoration, and at what concentration. A migration test measures how much of an element passes into the product, or into a food simulant, under set conditions of temperature and time.
The first shows what the container contains. The second shows what could leave it, which is the real question behind "can lead or cadmium leach into my product". Retailers asking for chemical safety evidence usually mean migration. A plant showing that it controls its batch is usually presenting composition.
Choosing the sample
| Question being asked | Sample that can answer it |
|---|---|
| Is the glass body acceptable? | Bottles from the production lot that will ship, not a laboratory-made trial bottle; the report should identify the lot or at least the production period |
| Is the ink, enamel or coating acceptable? | A fully decorated container, since a bare body says nothing about decoration |
| Is the closure or liner acceptable? | The closure as supplied, with its liner fitted |
For acidic, alcoholic or oily fillings, the migration conditions should reflect that product instead of a default aqueous condition. The migration testing page explains why.
What a usable report states
The work is done by elemental analysis, either of the material or of a migration solution. The recognised frameworks are the regulated procedures for glass and ceramic food contact articles and those for plastic food contact materials. A report you can rely on gives:
- the method;
- a description of the sample;
- the test conditions;
- the list of elements;
- each result set against the applicable limit;
- the laboratory's accreditation, the test date and the report number.
Watch for two weaknesses. A report limited to lead and cadmium, when your specification names a longer element list, answers a narrower question than you asked. A report with no sample description, lot reference or test conditions is a certificate and not evidence.
Screening table for supplier qualification
The table turns the four routes into questions for a supplier. Use it in full during qualification and in shortened form each time a shipment is released.
| Risk point | Source of the risk | What to request | Typical deflection | Follow-up question | Accept when |
|---|---|---|---|---|---|
| Colorant and glass composition | Metal oxide colorants plus refining and decolourising agents; loading climbs with colour depth and peaks in dark and opal ware | Statement of composition family, description of the colorant system, accredited report for the current colour and production period | "Our glass is food grade", "every colour is safe", "this report covers the whole range" | Which colouring system gives this exact colour? Can we see the report for this colour, and for which production period? | The report names the colour and glass family on the order, comes from an accredited laboratory, is current, and covers the full element list of the destination market framework |
| Decoration ink, enamel and coating | Organic inks, fired enamels, lustre and metallic finishes, sprayed coatings; restricted elements can sit in pigments, driers and metallic components | Declaration from the decoration supplier or decorating house, technical data sheet for the ink or enamel, composition or migration test on a fully decorated container | "The print is on the outside, so the product never touches it", "the ink is a reputable brand" | Which grade, from which supplier? Can the product reach any decoration when poured? Will the decorator issue its own statement? | The party that applies the decoration has declared, the grade is named, and the sample tested was fully decorated |
| Closure liner, gasket and seal | Liner compounds, plastisol, foil seal lacquers and elastomer gaskets in direct contact with the filling | Food contact declaration for closure and liner, material data sheet, migration test for fatty, acidic or alcoholic products | "It is a standard liner", "the closure supplier holds all the certificates" | Who makes the closure or liner, in which grade and thickness? Can the declaration be addressed to this article and not to a catalogue? | The declaration covers the liner grade actually supplied, agrees with the closure drawing, and the material suits the filling type |
| Recycled cullet share | Post-consumer and third-party cullet carrying crystal, leaded tableware, panel glass and lead-glazed ceramic fragments | Description of cullet sourcing, incoming inspection procedure, batch record with cullet source and share, composition test on production bottles | "Everyone uses recycled glass and it is good for the environment", "cullet has no effect on quality" | Where is the cullet from, how is it checked on arrival, is any rejected, and what does the batch record say for this lot? | The plant can describe a cullet source and an incoming control step, and a production composition test confirms the outcome and not just the intention |
Documents to hold before the first shipment
Four groups of documents make this risk manageable at the buying stage.
- Specification. Glass composition family, colouring route, decoration system if there is one, intended market and application, all in writing.
- Compliance statement. The supplier declares the article is intended for food contact, names the regulatory framework it declares against and states the limits met. The heavy metal statement is normally one part of the food contact dossier, not a replacement for it.
- Test evidence. Accredited laboratory reports on current production, with the sample described and the lot identified.
- Process evidence. Where cullet comes from, whether and how it is inspected on arrival, who doses the colourant and how, how a batch is identified and traced, and what happens when a batch result falls outside the expected range.
Few buyers request the fourth group, yet it is the best predictor of whether the next shipment will pass. A plant able to explain its cullet control procedure is a different supplier from one that can only hand over a certificate.
Tie the evidence to the purchase order
Put the commodity, colour, decoration route and destination market in the purchase order, and state that the supplier's declaration and current test evidence apply to that order. Should the colour, the decoration or the market change afterwards, renew the evidence, since any of the three can change the answer. A declaration collected once at the start of a relationship tends to end up covering a colour the buyer stopped ordering long ago.
Write the chemistry into the specification
Dimensions are not enough. Colour, glass family, decoration route, liner grade and destination market belong on the drawing or specification sheet, because each one restricts what the supplier may melt or apply. Ask for evidence on the article you are buying as well: a general certificate for a catalogue range proves nothing about one colour in one market, and that gap shows the first time a customer tests the pack.
Look both ways along the chain. Upstream, the glass plant must know what it has to comply with and needs controlled cullet and colourant supplies to do so. Downstream, the decorator and the closure maker are separate suppliers with their own materials, and the buyer is the only party with a reason to bring all three declarations together.
If the container itself is still undecided, weigh how much chemistry each option brings. A light-coloured stock bottle is simpler to document and re-test than a bespoke deep colour with two-stage decoration. Standard shapes with a settled composition are listed in our glass bottle collections. A catalogue page is no substitute for a laboratory report, but it helps narrow the chemistry question before you order.
Order of work when a customer or retailer sample fails
A failed chemical test is a containment problem as well as a laboratory one. The sequence of steps decides how much stock ends up at risk.
- Confirm what was tested, and against which limit. Obtain the full report, not the summary line. A result means something only alongside the sample description, method, conditions and limit. Check whether the sample was a bare container, a decorated one, a closure or a filled pack. Failures of the wrong test, or on the wrong sample, are common enough to rule out before any stock is quarantined.
- Hold the implicated material, not everything. A finding on a decorated article puts every pack from the same decorating run on hold, while undecorated bodies of that period are a separate question. A finding on the glass body means holding the production period the sample represents, which is why a lot or date reference on the sample matters.
- Pull the records for the held period. Compare the cullet source, the colourant batch and the ink lot with those of a period that passed.
- Decide what happens to the held stock. This usually runs alongside the investigation. The choices include re-testing by the same method, testing against the destination market framework if a different one was used, sorting the stock when only one colour or decorating run is affected, or diverting it to a market or application with a different limit.
- Turn the finding into a routine check. A cullet finding calls for a check at cullet intake, a decoration finding for one at the decorating stage, and a liner finding for the closure supplier's declaration plus a first-article test. Skip this and the same finding tends to come back within a year, often in another market and under another report.
The effect on the schedule is usually bigger than the technical work. A re-test can be quick. Re-decorating stock or changing a liner grade is a production event that has to be fitted into the existing plan. How to sequence that, and whether to change the liner, the ink or the glass, is part of the corrective path covered on the migration testing page.
What to send for a chemical safety file review
We work from two inputs. The first is the destination market; a pack sold in two markets may need two sets of evidence. The second is the glass specification: colour and depth, whether the composition is soda-lime, any decoration and the route used, whether the closure is lined and in which grade, and the cullet share the plant intends to run. Add the filling type and the conditions of use.
From these we draw up a file list for that pack. It sets out which declarations are needed and from which party, which test is meaningful on which sample, which rows of the screening table apply to the chosen colour and decoration, and what to ask the plant before a first production lot is committed. If a customer has already named a framework, market rule or retailer scheme, include it so the list is built against that requirement and not a generic standard. If a pack has already failed, send the complete report with sample description and test conditions. The same review can then establish what the result covers and which material to isolate while the cause is traced.
Frequently asked questions
Can glass packaging contain lead or cadmium at all?
It can, though seldom because of the base raw materials. The elements come in with colourants and refining agents, with cullet of uncertain origin, with inks, enamels, lustre and coatings, or with the liner or gasket touching the product. A clear, undecorated container is less exposed than one with heavy colour, a large share of uncontrolled cullet or multi-stage decoration.
Which matters more, testing the glass or testing the finished pack?
Both have a place. Composition testing is the plant's tool for controlling its batch and cullet. Migration testing reflects real conditions of use and is normally what a retailer or regulator wants to see. Where the pack is decorated or has a lined closure, those parts must be in the sample too.
Why are darker colours treated with more caution?
A deep amber, deep green, cobalt or black bottle uses more metal oxide than a pale tint, and opal or white glass may be a different glass system. Saturated colours also soak up more batch variation, so trouble in the colourant supply shows more readily. Dark containers are not unsafe for that reason. They do warrant a composition report for the exact colour, not one for the plant's lightest product.
Does recycled glass raise the risk of a heavy metal finding?
Cullet is not the problem; uncontrolled material inside it is, because melting does not remove leaded fragments. A plant with a known, inspected source and an incoming control step is managing the risk. One running unidentified cullet cannot predict its own result. Asking for the recycled share tells you little. Ask where the cullet comes from, who inspects it on arrival and what is done with a rejected load.
What should I ask for at quotation stage?
The four document groups described above: specification, food contact declaration naming framework and limits, fresh accredited test evidence that identifies the production period, and process evidence on cullet, colourant and traceability. A supplier able to provide all four is a stronger proposition than one offering only a certificate.
How do I keep the risk under control after the first order?
Treat chemistry as a specification item with a shelf life. Make the control agreed at qualification, or any later finding, a recurring check. Keep the declarations from the glass plant, the decorator and the closure supplier in one file per article, and review that file whenever a colour or a market changes.