I've been eyeing these blue bottles to paint for a while. I thought (briefly) about trying for accuracy and carefully drawing out the shapes before colouring, but being impatient and lazy, went straight in with the brushes, starting with very pale washes and building them up. The light, shapes and reflections changed constantly so I built up far too much, not leaving enough of the very light values in the glass. I was going to leave the background almost white, but felt I had to explain the brown shapes in the bottles, so bunged the door frame and brick paving in at the last moment, then regretted it.
I found a link some time ago on someone's blog on my list, to another blog where he gave some very good advice about painting glass - something about having three values, I think in a certain proportion - and it didn't much matter where you placed them, but if you did that, it would look like glass. And now I can't find either of those posts, so if anyone who reads this knows about that, I'd appreciate the link back again.