unscalable oldstyle numbers through \newfont with XeLaTeX (Minion)

Question

In what is below, the \newfont command does not scale the numbers. I would like to know why.

\documentclass{book}
\usepackage{fontspec}
\setmainfont[Ligatures={Common}, Numbers={OldStyle}]{Minion Pro}
\newfont{\myFont}{MinionPro-BoldCn.otf scaled 5000}
\begin{document}
\myFont 123456789 \Huge 123456789
\end{document}

Answer 1

\newfont is the (very) old LaTeX interface for defining a font, but it has always been a low level command. Higher level commands should be preferred when available.

The main problem with \newfont is that it defines a font at a fixed size.

However, fontspec provides \newfontface that looks like what you need:

\documentclass{book}
\usepackage{fontspec}
\setmainfont[Ligatures=Common, Numbers=OldStyle]{Minion Pro}
\newfontface{\myFont}[Scale=5]{Minion Pro Bold Cond}
\begin{document}
1234567890 \myFont 123456789 \Huge 123456789
\end{document}

(use the method that works for you in specifying the font name); I added also normal font digits for comparison.

All fontspec options can be added to \newfontface, for example old style numbers:

\documentclass{book}
\usepackage{fontspec}
\setmainfont[Ligatures=Common, Numbers=OldStyle]{Minion Pro}
\newfontface{\myFont}[Scale=5,Numbers=OldStyle]{Minion Pro Bold Cond}
\begin{document}
1234567890 \myFont 123456789 \Huge 123456789
\end{document}