Hi
I am of the view that the very pale, bluish-green dumps (made from good quality glass with flat polished bases) all came in a big crate (or several big crates) from China about 5 or 6 years ago: that is when most of them appeared in a burst in antique shops and on eBay, all in perfect condition (but labelled antique, and with antique prices of course). There are some paler Victorian ones, but these are of typical poorer glass with inclusions, and are yellow-green as opposed to blue-green. Hartley Wood made some reproduction dumps in the 1950 - 1970 period, I believe, but although of better quality glass they are closer to the Victorian style and colour than the Chinese ones.
I have seen a few clear glass dumps rather like the subject of this thread, and felt that they were modern rather than antique, given the excellent condition the surface was in - but I have no other evidence to back up that hunch.
Alan