Definitely not iridised, having compared iridised glass to vase posted. Currently investigating your suggested areas. I have temporarily ruled out Indian, having sometime researched this as a likely possibility. I am currently looking at Czech and Bohemian. Czech looks to me more likely but could be wrong. On close up inspection of the vase. There appears to be no coating of metallic salts during the heat process. Out of curiosity, if metallic salts were applied, would it be on the internal side of the glass vase too? The colour of the vase is questionable as to amethyst or aubergine as you have mentioned. I would of thought that amethyst would not be as dark as this and would allow natural light in order to determine it's true colour? I'm just asking.
Since that question, has now become contradictable. I have just held the vase in front of my monitor and noticed that there is an internal section that does allow light. With this in mind.......................... from the shoulder of the vase internally, width 3.5cm and the length approx. 11cm (close to the stem), this section is part clear and part amethyst.
I have also noticed faults, which to be honest I did not pay particular attention to before. The main vase outer area has very small indents with a pimple within the center, which would suggest to me that there was difficulty in perfecting the glass due to it's thickness. This may not be clearly visible on pictures taken.
Image against white background as per your request. Hope this will assist with possible identification.