Heavy Metal Migration Testing for Cutlery: Elements, Limits and Test Conditions

📅 Sep 04, 2026 👁 views

Migration testing is the technical basis of every food contact compliance claim for a metal knife. It is also the test most often misunderstood by buyers, who frequently order a report, receive a pass, and do not check whether the test conditions had any relationship to how the knife is actually used.

This article explains what migration testing measures, how conditions are chosen, and how to read a report critically.

What migration is

Migration is the transfer of constituents from a food contact material into food. For a stainless steel knife, the constituents of interest are the alloying elements and any impurities — chiefly chromium, nickel and manganese, and in some cases other metals. The transfer happens by corrosion and dissolution at the surface, which is why it is influenced by:

Factor	Effect on migration	Practical implication
pH of the food	Acidic foods accelerate metal release	Simulant choice reflects acidity
Temperature	Higher temperature increases the rate	Test conditions reflect cooking or hot washing
Contact time	Longer contact increases total transfer	Repeated-use protocols simulate lifetime exposure
Surface area to volume ratio	More contact area means more transfer	Test conditions specify the ratio
Surface condition	A rough, scaled or contaminated surface releases more	Why polishing and passivation matter
Steel composition	Higher free chromium in a stable passive film reduces release	Why grade selection matters
Chloride in the food	Chlorides break down the passive film	Salt and acidic foods are the worst case
Number of exposures	The first exposures typically release more than later ones	Protocols may specify three successive exposures

Food simulants

Simulant type	Represents	Used for
Acetic acid solution	Acidic foods	The most common simulant for metals, because acidic foods drive release
Ethanol solution	Alcoholic and some fatty foods	Less relevant for cutlery blade steel but relevant for some handle materials
Vegetable oil	Fatty foods	Fatty food contact
Water	Aqueous, neutral foods	Neutral foods
Saline solution	Salty foods	Sometimes used where chloride exposure is a specific concern
Distilled water, blank	Control	Establishes background

The exact simulant and concentration are defined by the applicable standard or by the laboratory under the relevant national scheme. For a knife, an acidic simulant is the standard choice because it is the worst realistic case for metal release and because most food contact with a knife involves acidic foods — fruit, vegetables, tomatoes, marinades.

Exposure conditions

Parameter	Options	How to decide
Temperature	Ambient, elevated, or a cooking-type regime	Based on the maximum realistic use temperature. A knife used for slicing at room temperature differs from one used for hot food
Duration	Minutes to hours, or a defined short contact	Based on realistic contact time
Number of exposures	Single or multiple successive	Repeated-use articles are normally tested repeatedly to represent lifetime use
Surface area to volume	A defined ratio	Defined by the standard; a whole knife in a small volume is a harsh ratio
Preparation before testing	Cleaning, passivation, simulated use cycles	Should reflect what the customer does, or the standard's requirement

Limits and where they come from

Element	Concern	Limit source	Typical treatment
Chromium	Alloying element in all stainless grades	National measures; Council of Europe guidance; other national standards	Usually comfortably met by a well-finished and passivated steel
Nickel	Alloying element; also a skin sensitiser	National measures for food contact; separate restriction for prolonged skin contact	Both food contact and skin contact should be considered. See nickel release
Manganese	Present at higher levels in some cost-reduced grades	National measures	A driver of failure when cheap grades are substituted
Iron	Not a health concern at normal levels	Generally not limited	Appears in results; not usually decisive
Lead and cadmium	Contaminants, or present in coatings, prints or solders	Strict limits in several regimes	Relevant for coated, printed or brazed products
Aluminium	Aluminium components	National measures	Aluminium is a poor choice for a knife blade in any case — see below
Arsenic and other trace elements	Impurities from scrap	National measures	Relevant where recycled or scrap-derived material is used without control

Where migration failures actually come from

Cause	Mechanism	How to prevent
Surface contamination	Grinding residue, polishing compound, oil, embedded iron particles	Specify and verify cleaning and passivation
Embedded foreign particles	Iron or carbon steel particles embedded from tooling or from a shared grinding line	Segregated tooling; cleaning; passivation; inspection for embedded particulate
Inadequate passivation	A freshly ground or blasted surface has a disrupted passive film	Passivation treatment after blasting and grinding, with verification
Wrong grade substituted	A cheaper grade with a different composition	Incoming material control and mill certificate verification
High-impurity or scrap-derived material	Trace elements above intended levels	Specify a mill and grade; require certificates; test periodically
Brazing or solder residue	Filler metal at a joint in the contact zone	Specify a compliant filler; require cleaning; consider isolating the joint from the contact zone
Coating defects	A coating that is porous or poorly adhered releases more and can expose the substrate inconsistently	Coating thickness and adhesion control; visual inspection
Rough finish	Increased surface area and retained residue	Finish specification and consistent execution. See surface finishes

The most under-appreciated cause is embedded particles. A blade ground on a line that also processes carbon steel can pick up iron particles that later rust and appear in a migration result as anomalous. This is a real phenomenon and the control is material segregation on the line, not a change of steel grade.

Reading a migration report critically

What is written	Why it matters	What to do if it is missing
The material and its grade	Determines whether the report applies to your product	Ask for the composition or a substitution test
The simulant and its concentration	Determines whether the test represents your product's use	Ask why that simulant was chosen
Temperature and duration	Determines worst-case coverage	Ask whether the conditions cover hot use and washing
Number of exposures and how the result is expressed	Determines whether the report addresses repeated use	Ask for a repeated-exposure protocol if the product claims long life
Surface area to volume ratio	Determines comparability	Ask for the ratio and whether it reflects a realistic use
Sample preparation	Determines whether the tested sample matches production	Ask whether the sample was production-representative or specially prepared
Measurement method and detection limits	Determines whether a "below detection" result is meaningful	Ask for the detection limit relative to the applicable limit
Laboratory accreditation	Determines the weight of the result	Ask for the accreditation scope
Date and report number	Determines validity and traceability	Ask if the material has changed since

"Not detected" is only meaningful alongside the detection limit. A method with a detection limit above the applicable regulatory limit cannot demonstrate compliance, no matter how good the result appears. This is a technical point that has caught many buyers, and it is easy to check: ask for the detection limit and compare it to the limit being applied.

Passivation and finishing

Operation	Effect on the passive film	Requirement
Machining and grinding	Disrupts the film and can embed foreign particles	Cleaning after grinding
Bead or sand blasting	Increases surface area and disrupts the film; media can embed	Passivation after blasting, and media control
Pickling	Removes scale and embedded contamination	Followed by rinsing and passivation
Passivation	Rebuilds a uniform chromium oxide film	Specify the treatment and verify the result, for example by a water-break or a copper sulphate test, or by a migration test
Polishing	Generally improves the surface but compounds must be removed	Cleaning and degreasing after polishing
Washing and drying	Removes residue and prevents chlorides from being trapped	Specify water quality, rinse stages and drying

For a blasted or stone-washed blade, passivation is not optional. A blasted surface has a disrupted film and a high real surface area, and it will release more than a polished surface unless it is passivated. If a factory blasts and does not passivate, the migration risk is materially higher, and the visual appearance gives no clue.

Specifying migration testing

Name the market and the framework the test is intended to support.
Identify the material by grade.
Specify the simulant or ask the laboratory to justify the choice.
Specify the temperature and duration, or require the laboratory to select conditions appropriate to repeated food contact with acidic foods.
Require a repeated-exposure protocol.
Require the detection limits to be reported and to be below the applicable limits.
Require the sample to be production-representative, with the finish as sold.
Require the report to state the surface condition, since finish affects the result.
Use an accredited laboratory and require the accreditation to be identified.