Diving terminology is sometimes difficult. Is it a mask or goggles? Should we say fins or flippers? Dived or dove? And then we throw in words like “viz” and downtime. But the one that is always contested is that thing we strap to our back. Whether you call it a tank, bottle or a cylinder there is still the matter of what it is made out of. If you use steel than there is no problem, but if you use that other material than you really have to watch what you say.
As a PADI diving instructor when teaching open water courses to divemaster trainees I have to talk about tanks a lot. There is always a moment where I look at my students and assess exactly what to say to them. Should I tell my open water student about the tensile strength of their tank or just that it is filled with compressed air that they will allow them to breath freely underwater. As for my eager divemaster trainee it would be wise for me to tell him everything I know about tanks, after all one day he will become a PADI instructor and will pass the wealth of information I give him to his future divemasters! If you say Aluminum to a Brit you will have them politely correcting you almost instantly. Say Aluminium to an American and you get a strange look. So what is the “correct” term? It’s actually a bit of an interesting story.
First a little bit about the substance itself. It is amazing that we can’t decide what to call this stuff; after all it is the third most abundant element found on the planet, and happens to be the most abundant part of the Earth’s crust. Only Oxygen and Silicon are found more often. But don’t expect to wander around and find some lying in the dirt. It bonds well with oxygen, silicone and other minerals and tends to stick to them like hair on bubble gum. For that reason it is not found naturally, it is always combined with something else. Even though it was “discovered” in 1807 it had been an integral part of some cultures for centuries. Egyptians and Babylonians used a compound to dye cloths and produce some makeups. In Persia it was the secret behind their high quality clay pots, Teflon would come later (much later). But it wasn’t until 1825 that someone could actually manage to hold up a small clump of the stuff and get a picture to put up on the periodic table. That man was Hans Christian Oerstad from Denmark. Two years later Friedrich Wohler managed to isolate it in an even more pure form. Despite both of these men being in contention for “discovering” the element, neither got the opportunity to name it.
Sir Humphrey Davy a British chemist from Cornwall had the honor of giving the element a name back in 1807. Considering how 
quickly everyone from the United Kingdom jumps on my back (being a Canadian) for saying “Aluminum” it’s interesting to find out what Sir Humphrey decided. As with most science type words it of course originates from the Latin word for alum or alumen to be precise. As it turns out none of us use the original name that Davy proposed. Alumium was his first choice. But Davy wasn’t done yet. He then decided that perhaps it should be changed to Aluminum. His scientific friends were not happy with him however. It seems that Aluminum just doesn’t chime well with Sodium or Potassium or Magnesium (all of which Davy named). So in 1812 he changed his mind again and went with Aluminium. All of this fickle mindedness is the root cause of why we can’t seem to agree on what to call the stuff. But what do you expect from a guy like Davy. This is a man that once locked himself in a box and filled it with Nitrous Oxide in order to “produce excitement equal in duration and superior in intensity to that occasioned by high intoxication from opium or alcohol.” He then named that particular gas, “laughing gas.” Ahh science.
Fortunately no one was calling it much of anything as it was very hard to produce. It was actually considered a precious medal (like Gollum’s ring) for a while. Then around 1895 it started to drop in price and was able to be manufactured. All of a sudden people needed to actually use the name. In the states everyone looked to the Webster’s Dictionary for the correct spelling. For whatever reason that book still had the Aluminum version. And that’s the version that was picked up. Brits used the melodic Aluminium instead. In 1990 the International Union of Pure and Applied Chemistry (IUPAC) settled on Aluminium but thought it best to include the Americans, so brought in Aluminum as an acceptable variation three years later.
So who is correct? Both I guess. The American version was in use before the British, although it was coined by Davy (a Brit). Doesn’t really clear things up does it? Guess you’ll just have to say it however you want and dig your heels in. The way you say it is fine.
But fins go on your feet and Flipper is a dolphin.
