9ct Rose gold tested as Copper

[handmadeblanks]

Unless I'm mistaken, the most accurate method of testing--Cupellation--is a destructive test so it's not something you would want to perform on a finished piece of jewellery. Since the OP bought the wire from Cookson I would say the onus is on them to verify the purity in a dispute. (I'm not an expert in Law but I did a lot of research on product liability before selling anything)

In any dispute, such as the OP has experienced, the final retailer would require to show due diligence. For me, because I make my own alloy mix, I send a sample to the LAO to have it tested using the most accurate method possible, regardless of whether it is destructive or not. I then have a record as evidence of my due diligence.

Of course the solution would be to have everything hallmarked after it is made, but I think that unnecessarily increases time and cost of getting the final item to market.

[ps_bond]

Unless I'm mistaken, the most accurate method of testing--Cupellation--is a destructive test so it's not something you would want to perform on a finished piece of jewellery.

While that's true, you don't generally have the entire piece tested that way... That would be rather silly. When it is done - and none of the pieces I've submitted over the past 15 (ish?) years have been subjected to this - a small sample is removed from an inconspicuous area (or so we hope) and the assay is done on that sample. The refined sample is then returned along with the hallmarked object.

In a similar vein, it used to be that objects failing hallmarking were destroyed; now they're invariably (wriggle room for the occasional exception) returned.

[CJ57]

It is how it used to be tested at Edinburgh Assay Office back in the day. They took such dreadful scrapes from every surface that it was common practice not to send in anything finished and more often no more than soldered but pickled sometimes even with all the component parts. Sometimes it was difficult to recover the scraped areas