Mark from New Bedford, Massachusetts has sent us photographs of some beautiful window panels with red pictures of grapes and vines. He would appreciate any information anyone can supply about where they may have been made, when, and what their value could be. They are smooth on the front with a raised pattern on the reverse side. There has been some discussion recently about glass changing colours under certain kinds of light, and this feature being used to deceive people into thinking they have found a rare colour. When irradiated, antique glass with manganese turns deep purple.
Antique glasses are capable of turning many other colors.
It is not known exactly what elements, other than manganese, produce what color changes. Technical journals written on glass irradiation discuss only late 20th century present day glass formulas, not old glass formulas. Everything seems to evolve around knowing the formulas for the glass. It was interesting to learn that, according to ACRN, pieces of glass can be sent to a lab to determine whether the glass' color is created by chemical ingredients or irradiation. And I have not seen it in New Zealand.