Thank you M for the research efforts. In a way I am quite pleased that the light blue transparent inner glass is so elusive to find examples of as it confirms how unusual it is. I have contacted a couple of people who may know something on this subject and I hope they will get back to me with some more information. I will get a copy of CH 1800-1914, in the next fortnight, though I can access a copy locally sooner than that. If I hear or learn anything more, I will let you know!! It is funny, given how many examples there are of this general technique, that this colour combination cannot be found! Thanks again,
Robert (bOBA)