We machined the first generation of the note from an aluminum alloy called 6061. It was an easy choice. 6061 is very easy to machine, so we could shape it exactly how we wanted. It's also light, so the note is easy to carry anywhere. We anodized it to further protect it.
Anodizing is a wonderful process. You dip the aluminum in a bath, run an electric current through it, and the metal's surface forms a thin skin of aluminum oxide. That skin is a ceramic, and it's the same material sapphires are made of. This is why Apple anodizes their aluminum products. The surface is closer to a gemstone than to a metal, and very hard to scratch.
So we were surprised when our notes started to scratch after some use.
We tried different types of anodizing, thicker and harder, and it kept happening. The problem turned out to be the metal underneath, not the shell. 6061 is a softer metal, and a thin ceramic over a soft metal is like ice over mud. Ice over concrete doesn't break when you step on it. Ice over mud cracks. When the aluminum underneath dented, the ceramic skin above it cracked, and that was the scratch we were seeing.
So the metal had to change. We swapped to a 7000 series aluminum called 7075, the kind used in aircraft. It's aluminum mixed with zinc, nearly twice as strong as 6061, and it weighs almost the same. Apple made the same move years ago. When phones started bending in pockets, the iPhone switched to the 7000 series. Now our ceramic skin sits on a hard metal surface, and it stays rigid for much longer.
Making it the right color took just as much work. Anodizing doesn't paint the metal. The ceramic skin is covered in tiny pores, and the color soaks into those pores before the surface is sealed, so it’s deep inside the skin and can't chip off. We tested two colors for a long time. A deep black, which took a lot of tuning to get dark and even. And a natural one, a silver with a hint of gold in it, close to the color of titanium. The natural was the harder of the two. There's no dye to help you, so every flaw in the metal shows. But when you see it next to the brown leather, you understand why we chose it.
The trade is that the 7000 series is harder to machine, so each note takes longer to manufacture. But the note lives in pockets with keys and dirt, and the pen clicks in and out of it thousands of times. The surface needed to stay the way we made it for years, and now it does.
The scratches were small, and most people would never have noticed. Now we are happy we are able to make the product we always wanted.
A Brief History of Aluminum
The Ballpoint Pen