[XeTeX] Using Gentium with XeteX

[Till Rettig]

Hello,

I started using Gentium a while ago with XeteX, but realized, that there 
is a caveat I cannot solve: The font comes only in two faces: normal and 
italic. How do I achive bold face? In openoffice or ms word this is no 
problem, the program obviously has some font information that lets it 
scale the fonts accordingly. Is there any option in the fontspec package 
that let you do the same? I guess the idea behind this is, that italic 
face has different shapes while the bold version is only a scaled 
version of the normal or italic face where all lines are scaled 
accordingly. It seems the font designer thought this method is good 
enough to get sufficient results. But how do I tell XeteX to do the same?

Thanks in advance
Till Rettig