This is an interesting discussion.
My first comment is that "DG" does not stand for "Dennis Glassworks". It stands for "Decorative Glass Co., Amblecote, Stourbridge"
Ok, that sounds as if I am very knowledgeable on the subject. Not true! I checked the Patent reference as located by Frank and then went a stage further since there is a reference to an earlier Patent (128229) in which it is stated: "128,229. Guest, A. H., (trading as Decora- tive Glass Co.). Nov. 21, 1916."
[It's a pity that the full Patent details, as displayed in Adobe Acrobat (pdf file), do not include the referenced drawings.]
To begin with, I thought a mistake had been made by linking the Hartmann reference to the "DG Ware" mark, since Hartmann's reference is to a label "Stourbridge DG", which is taken directly from Cyril Manley's book "Decorative Victorian Glass" (page 125). And Manley, as far as I can see, does not refer to "DG Ware". And that name is not shown in any of my other books, either!
However, from the other entries on this thread, there does seem to be a positive link to Harry Guest's patents and the "DG Ware" label, showing that these are probably all from the Decorative Glass Co. My reasoning is that on page 99 of Manley's book, the entry for a vase (no 327) is as follows:
A fairly common type of glassware, all signed D. G. Stourbridge (the trademark is shown on page 125). The idea was to insert pictures between glass casings. Generally, these are, in my opinion, not worth collecting, but Mr Guest, the patentee, made some pictures from feathers and these I think should be collected. I have been told that some very beautiful pictures were made from butterflies' wings.
So, it all seems to tie together - and perhaps this board has identified a label that I, at least, have not seen attributed in any of my reference books.
The item seen by "paradisetrader", with the butterfly wing decoration is presumably one of those that Cyril Manley (at the the time of preparing his book) had not seen personally. I'd love to see a photo of that piece.
Incidentally, butterfly wings are also believed to have been used for decoration representing such as stained glass windows in cathedrals in some of the Victorian / Edwardian gift paperweights - the type with a picture applied to a flat base and covered with a low glass dome.