When you create a window with multiple glass panes, you should be able to choose the type of material for each of the panes that you create. You can select individual panes to be a sash, or top hung, or bottom hung etc. but only one choice for materials. You should be able to select the material for each pane. As some have glass and other panes in the same window can be blacked out or obscure.
As a workaround you can simply make a slab with the surface you want and save that as a window 'filling', and pick this custom library part for the window 'rotating part'. I'm sorry I do not know the term that is used in the English language versions.