\column \override #'(font-name . "Arial Bold") {
D A F♯ D A D
}
Using `font-name` is 'absolute', that is, it overrides any LilyPond
font switching mechanism. This means that `\number` doesn't work.
There are two solutions: Either set up a font tree so that you can use
standard commands like `\bold` (and `\number`), or switch manually to
the `Emmentaler` font. An example for the latter is
```
\column \override #'(font-name . "Arial Bold")
{
D A \concat { F
\override #'(font-name . "Emmentaler-16") \small
♯ } D A D
}
```