Well, unlike any other kind of glass - cut glass is not clear but it does share with all glass some specific qualities, those being the hard, strong highlights and hard, dark accents. This is where standing by your method will be the only thing that saves you. Go for the SHAPES- and in this case I first painted the little pitcher as a mid-value shape, then broke up that shape into smaller shapes of light and dark, leaving room, value wise for brighter highlights and darker accents. The colored brush on the inside of the pitcher is used as device to hint at some clarity characteristic of glass; and I faked it a bit to better communicate. The red I actually saw was very obtuse. Here, I fall back on my first rule of any still life: it has to communicate to the viewer. The short hits of red suggest that the pitcher has some clarity (as opposed to being opaque) and that the brush inside extends to the bottom.
In class, we all agreed that cut glass was the hardest subject in the glass category; the brush was fun tho'.