[XeTeX] Special fonts in math environment?

[Dervin Thunk]

Hello:

I'm using XeLaTeX version:

XeTeX 3.141592-0.996-patch1 (Web2C 7.5.6)
kpathsea version 3.5.6
Copyright 2007 SIL International.
Kpathsea is copyright 2007 Karl Berry and Olaf Weber.
Compiled with ICU version 3.4 [with modifications for XeTeX]
Compiled with zlib version 1.2.3.3; using 1.2.3.3
Compiled with FreeType2 version 2.3.5; using 2.3.5
Compiled with fontconfig version 2.5.0; using 2.5.0
Compiled with libpng version 1.2.15beta5; using 1.2.15beta5
Compiled with libpoppler version 3.00

on Ubuntu.

I was wondering if I'm doing something wrong here. I have

\newfontinstance{\gothic}{MPH 2B Damase} % gothic

and although {\gothic \U+10330}, $\frac{{\gothic \U+10330}{234}}$ does
not. Is this a technical limitation or am I doing something wrong?

Thank you.

Dervin