Recently we did something we had never done before.
We test our products all the time, from different angles and with different methods, always looking for ways to improve quality and durability. But this test was different. This one didn't start with us. It started with a challenge from someone else.
One of our retail partners forwarded us an email from a customer who had bought one of our copper water bottles. In their own words:
"I just checked the density of the copper water bottle using the displaced water method. I get a density of 7.5 g/cm³. Copper has a density of 8.96 g/cm³. Given it's an imperfect test some differences would be OK, but 17% is too much. The bottle is not pure copper."
That message hit us hard.
We're a Certified B Corp. We pride ourselves on quality and sustainability, and we genuinely believe we live by those values. Every copper product we sell is tested at reputable, world renowned labs. Our manufacturing partners know we start from quality, not price, and work backward from there. So a challenge like this one went straight to the core of who we think we are.
We could have replied with a polite explanation and moved on. Instead we decided to prove it, to ourselves and to our customer.
Simple in theory, harder in practice
We started by looking into how to properly test copper density at home. On paper, the water displacement method is simple: weigh the object, measure how much water it pushes aside, and divide one by the other. In practice, it fought us at every step.
The first problem was equipment. We needed a tall, narrow container with measuring lines, big enough to submerge a 950 ml bottle. We couldn't find one online in time, and a trip to Bunnings turned up nothing tall enough either. So we bought a 30 litre bucket instead and tried weighing the displaced water on our parcel scale.
The numbers were nowhere close. Every time we checked a reading, it was clear something was off. It took a few attempts before it clicked: our scale was far too imprecise and our container far too large for the tiny volumes actually involved.
Second attempt: a kitchen scale and a smaller measuring jug. Better setup. Still, the results weren't adding up.
The turning point: we weren't testing the copper
Then came the theory that changed everything. Trapped air.
A sealed, hollow bottle has plenty of places for a pocket of air to hide, under the base, in the cap threads, along a seam. For an object this small, even a tiny air pocket can throw a density reading off by a lot. To test the idea, we ran the exact same method on a solid copper tongue cleaner instead, with no cavity and no seams. The result came back almost perfect.
That confirmed it. We weren't testing the copper. We were testing the shape.
So we bought a pair of metal snips and cut open one of our own bottles.
We removed the neck section first to get the cap threads out of the way, then cut the body into pieces. One section tested well straight away. The other, a curved, cup shaped offcut, still came back low. So we cut that piece again, into two smaller, flatter sections, and tested each one on its own.
This time every number landed right where it should. Genuine, high quality copper, confirmed piece by piece.
It took six to eight hours of running around, from Bunnings to Kmart and back to the warehouse, working until 11pm on a Friday night. But the peace of mind afterward made every minute of it worth it. We can now go back to our retail partner with real evidence, not just reassurance.
The science behind the test
If you want to understand why the shape mattered as much as the metal, it helps to know what density actually measures.
Density is simply how much mass is packed into a given space, measured in grams per cubic centimetre. Every pure metal has a fixed density, decided by how tightly its atoms pack together and how heavy each atom is. Copper atoms are heavy and pack closely, which gives pure copper a density of 8.96 g/cm³, no matter what shape the copper is in. That fixed number is what makes density such a good purity check. If something claiming to be copper is mixed with or replaced by a lighter metal, the overall density drops in a predictable, measurable way.
The reason water is the tool for measuring it goes back to Archimedes. Any object submerged in water pushes aside a volume of water exactly equal to its own volume. Weigh the object dry, measure how much water it displaces, and you have both halves of the density equation, mass and volume, without needing to calculate the volume of an awkward shape like a bottle by hand.
The catch, and what tripped us up, is that this only works if the water is touching every part of the object's surface. Any pocket of trapped air behaves like invisible extra volume. It makes the object seem to displace more water than the metal really does, which drags the calculated density down even though the metal itself hasn't changed at all. That is the whole reason a genuine copper bottle can read low, while the same copper cut into flat pieces reads exactly right.
Why we're sharing this
This whole experience was a genuine education, the kind you don't get from a lab report or a textbook, and we're grateful for it. Grateful to a customer who cared enough to check the numbers themselves and to push us to prove it rather than take our word for it.
That is exactly what the world needs more of: products built to be questioned, tested, and trusted, not ones designed to look good on a shelf for a few weeks before ending up in landfill.
With integrity comes trust. So thank you to everyone who holds us to that standard. Keep asking. Keep checking. That is how we all get better.
If you ever test one of our products and get a result that concerns you, we genuinely want to hear about it. You can reach us any time at dogood@goodlygosh.com.au.