A salt spray requirement on a metal souvenir order is a specification, not a slogan. “Must pass 500 hours” is meaningless unless the purchase order also names the standard, the atmosphere and the acceptance criteria. ASTM B117 and ISO 9227 share most of their mechanics but not all of their atmospheres, and a report that omits the acceptance criteria tells you nothing about whether the goods passed. This guide covers how the two standards work, what durations buyers actually specify, and the sentence that has to appear in the purchase order if you want a result you can rely on.
Metal souvenirs spend their lives in places where ordinary consumer goods do not. A souvenir fridge magnet lives on a fridge door in a coastal rental flat, in a seaside gift shop window, or in the glovebox of a hire car. A bottle opener keychain gets carried on a boat. A challenge coin goes into a golf bag. None of them live in a dry living room, and the ones sold in seaside destinations sit in salt-laden air for months at a time.
That is why a corrosion requirement ends up in metal souvenir orders more often than buyers expect. The requirement usually arrives as a sentence in an email from the retailer’s technical team, or from a brand’s packaging specification, and it frequently arrives without the detail needed to make it testable.
What the Salt Spray Test Actually Does
The test puts specimens in a chamber and exposes them to a controlled salt fog. A 5 percent sodium chloride solution is atomised and sprayed into a sealed chamber held at 35 degrees Celsius. The fog settles on the samples at a controlled rate, and the samples are withdrawn at intervals and examined for corrosion, blistering, peeling, and how far corrosion has crept from any scribe line cut into the coating.
The method is a proxy, not a simulation. It is designed to be repeatable rather than realistic, which is exactly why two laboratories running the same standard should produce comparable results, and why the numbers are comparable across suppliers.
The reference guide to ASTM B117 practice sets out the chamber mechanics in detail, and the standard itself is published by ASTM. In Europe the reference is ISO 9227, and this laboratory’s side-by-side explanation of the two standards is one of the clearest treatments of where they diverge.
Where ASTM B117 and ISO 9227 Diverge
Both standards share the same core method. The 5 percent salt solution, the 35 degree chamber, the neutral pH band, the controlled deposition rate and the specified sample angle are effectively the same in both. The difference is in the atmospheres and in how results are reported.
| Parameter | ASTM B117 | ISO 9227 |
|---|---|---|
| Atmospheres available | Neutral salt spray (NSS) only | Neutral salt spray (NSS), acetic acid salt spray (AASS), copper-accelerated acetic acid salt spray (CASS) |
| Salt solution | 5 percent sodium chloride in water | NSS 5 percent NaCl; AASS and CASS add acetic acid, with copper chloride in CASS |
| Spray solution pH | 6.5 to 7.2 | NSS 6.5 to 7.2; AASS and CASS around 3.1 to 3.3 |
| Chamber temperature | 35 degrees Celsius | 35 degrees Celsius for NSS and AASS; 50 degrees Celsius for CASS |
| Deposition rate | 1.0 to 2.0 ml over 80 square centimetres per hour | Same collection area and rate, verified with collector funnels |
| Sample angle | Specimen face inclined 15 to 30 degrees from vertical | Same inclination, with the position inside the chamber also specified |
| Suggested exposure periods | Set by the specification, commonly 24 to 1000 hours | 2, 6, 24, 48, 96, 168, 240, 480, 720 and 1008 hours |
| Result reporting | Visual assessment against the buyer’s criteria, often graded to ASTM D610 for corrosion and ASTM D714 for blistering | Rating alongside the test standard, with the atmosphere and duration always stated |
Two practical points follow from the table. First, if a supplier quotes a report in hours without naming the atmosphere, the report is incomplete, because “48 hours” means something quite different under NSS and under CASS. Second, decorative plating is the case where the accelerated atmospheres earn their keep: AASS and CASS are the more aggressive routes for copper-nickel-chrome decorative systems, which is where a plating failure shows up first.
Choosing a Duration: The Bands That Buyers Actually Use
Durations get quoted in round numbers because laboratories and specification writers think in bands rather than in exact hours. The bands below are the ones that appear repeatedly in real purchase orders, together with what they are reasonable for.
| Exposure | Typically required for | What a failure at this point tells you |
|---|---|---|
| 24 to 96 hours | Basic screening of plating quality, indoor items, general merchandise | The coating system is fundamentally weak or poorly prepared |
| 240 hours | Moderate durability requirements, indoor promotional goods with occasional handling | Coverage is inconsistent, or the pre-treatment was inadequate |
| 480 to 720 hours | Coastal and outdoor exposure, matching the ISO 9227 corrosivity categories for marine and coastal atmospheres | Under-plating, thin protective layers, or copper showing through |
| 1000 hours and above | Demanding durability requirements and specification-driven qualification | The plating system does not suit the environment at all |
ISO 9227 also provides a way of linking an exposure duration to an environment, through its corrosivity categories. The C1 to C5 scale runs from very low corrosivity, such as dry indoor interiors, through to very high corrosivity in tropical marine atmospheres. The C4 and C5 bands correspond to coastal and marine conditions and are associated with the longer exposure periods in the table above. That is the language to use when you want a test tied to where the product will actually sit.
Buyers sourcing from Chinese factories will also meet reports written against GB/T 10125, the Chinese national standard that adopts ISO 9227 and adds assessment rules for aluminium alloys, including a rating scheme based on corroded surface area, where under 0.1 percent corroded area corresponds to the highest rating and above 50 percent to the lowest. A factory report in that format is a perfectly good document. What matters is that it states the standard, the atmosphere, the duration and the acceptance criteria, and that the sample came from the production lot rather than from a showroom piece.
The Line That Buyers Misread
There is a persistent claim in the industry that a specified number of salt spray hours corresponds to a number of years of service life. It does not, and any supplier who offers that conversion is telling you something you should factor into your decision about who to work with.
The reason is straightforward. Salt spray is a fixed, aggressive laboratory environment with a constant temperature and a constant chemistry. Real exposure depends on climate, humidity swings, ultraviolet exposure, how often the item gets wet and dry, whether the coating gets scratched by handling, and whether anyone maintains it. A lab result of 500 hours is a statement about how the coating compares with other coatings under the same test, not a forecast of how many winters a souvenir shop in Cornwall will see.
This does not make the test useless. It makes it useful for the thing it is actually good at, which is comparing surface treatments against each other and catching process faults early. Poor pre-treatment, uneven plating thickness, contamination before plating, and over-polishing that has thinned a protective layer all show up quickly under salt spray. Those are exactly the defects that cause a metal souvenir to look corroded on a shelf within a season.
What the test will not tell you is whether the particular bronze or antique finish you have specified is the right aesthetic choice, whether the colour will match the rest of your range, or whether the weight and balance are right in the hand. Those come from physical samples, which is a separate subject and one worth handling at the same time.
What to Write in the Purchase Order
The clause below is the minimum that produces a usable report. It is short because a purchase order is not the place for a standards summary, but every element of it removes one way the result can become useless.
Plated components to pass a neutral salt spray test to ISO 9227 NSS at 480 hours exposure, with no corrosion of the substrate, no blistering and no peeling, and corrosion creep from any scribe line not exceeding 2 mm. Test pieces to be drawn from the production lot, cut from the same plating lot, and the full report to state the standard, the atmosphere, the chamber conditions, the exposure duration, the inspection points and the acceptance criteria applied.
The elements worth noting are the scribe line requirement, which is what turns “no visible rust” into a measurable pass or fail, and the instruction that samples come from the production lot. A report on a sample from the factory showroom tells you the showroom piece survived. A report on a piece cut from the production run tells you the process is under control.
Summary Table: What to Specify by Environment
| Where the product lives | Standard and atmosphere | Exposure | Additional note |
|---|---|---|---|
| Indoor gift shop shelf, dry climate | ASTM B117 or ISO 9227 NSS | 24 to 96 hours | Screening only; confirm colour and finish by physical sample instead |
| Indoor promotional use, handled frequently | ISO 9227 NSS | 240 hours | Ask for scribe line and creep limits |
| Coastal town, seaside attraction, marina retail | ISO 9227 NSS, C4 corrosivity context | 480 hours | Specify double plating or a protective clear coat where available |
| Tropical or beachfront destination retail | ISO 9227 NSS, C5 corrosivity context | 720 hours or above | Under-plate thickness becomes the deciding factor; ask for the plating spec |
| Decorated retail piece with an antique or bronze finish | ISO 9227 NSS, plus visual reference | 240 to 480 hours | Antique finishes are chemically treated surfaces; corrosion resistance and colour stability are separate questions |
| Decorative chrome or high-gloss plating | ISO 9227 AASS or CASS | Per specification | Use the accelerated atmosphere for decorative plating systems |
Two closing points on the practical side. If the finished piece carries an enamel or painted surface, the salt spray result describes the plating underneath, not the colour on top, so the test should be specified on the relevant component. And if you are ordering from a factory that has never run this test on your part before, ask for a test piece from the first batch rather than waiting for the production run; the cost of one qualification sample is trivial compared with a container held at the port.
For the decorative side of the same decision, the plating options available for custom metal products are covered in our guide to plating options for custom metal keychains, and the checks that should sit underneath any corrosion requirement are in our article on quality control for custom metal gifts. For the specific castings used in the souvenir trade, see our custom metal souvenir range, which includes the 3D landmark models and miniature buildings that make up most destination merchandise programmes.