I was talking to a fellow artist about drawing and painting glass. We discussed whether it has a blue tinge like water but I disagreed. I suggested he looked at the reflection on glass. Sometimes glass is tinted slightly, uranium glass for instance is yellowish, I said I thought it depended on what is added to it when it’s manufactured. I think if you were to put a glass and a plastic bottle next to each other as an exercise and draw what you see you would probably notice stronger reflections on the glass. Also look at shadows, glass, though usually transparent, throws a shadow…instead of using blue to define it I said try using a bit of grey. Observation is very important.