Creating a font based on the GTK default font

[Dominic Sacré <bugcreator gmx de>]

Hi,

I'm looking for a way to get the GTK default font - i.e. the font which is 
normally used for all GTK widgets - and to create a new font based on 
that. For example, I want to use the same font for a widget, but bold 
and/or italic, or the same font at a different size. How can I do that?

I guess I need to get the font's desciption (how?!), and then modify that 
string somehow, but maybe there's a better and easier way?

Thanks in advance,
    Dominic