I cannot find my first edition of that book, most annoying, I seem to have lost it. I understand what is said, but the cameo on these pieces is cut in relief with the blue and white layers being raised against the clear background. Also the veins on the leaves and the stems are also in relief on the blue. not engraved to look as though it is relief. I shall go and do a quick search to look at antique glass with intaglio engraving and have another look at the differences.
on another note -
This vase with a goat and vines and grapes was sold at Sotheby's in 2007 attributed to Franz Zach.
I can see similarities with my decanter in this piece. If this piece is indeed Franz Zach (there are similarities with this piece and another signed Franz Zach vase which I guess is what they base their attribution on) then, despite what the V&A have said, I think he has to be in the running as a possible for my decanter.http://www.sothebys.com/en/auctions/ecatalogue/2007/an-important-private-collection-from-hanover-am1020/lot.962.html
My decanter is incredibly well made and decorated. There is no evidence of any shoddy work at all, it is quite impeccably made and engraved/cut and finished.
I have now searched well in excess I estimate of 3000 images of bechers, flakons, decanters, vases, pokals and steins etc, through various auction houses, museum collections and books going back a number of years. There are only three makers names that come up and they are Karl Pfohl, Franz Zach and Ernst Simon (n.b. I've not found the reference for Ernst Simon's piece in the Corning as it was previously attributed to possibly Franz Zach). They may or may not be the only makers.
Whilst it may be the case that the unknowns are always in the majority, and that does need to be borne in mind, these two layers red or blue over clear matt cameo glass remain incredibly rare pieces, museum pieces as far as I can see.
The three layer matt cameo pieces are even rarer so far. Those with the grapes and vine I have found so far are two bechers, my flakon(decanter) and one( possibly two - picture too indistinct to see properly) steins.
With regard the bechers, of the leaves that it is possible to see on the photos they do not have the curled up edges that the leaves on my decanter do, and one of the photos is not a good one so it's difficult to be sure, but the smaller one when placed side by side with my decanter in a photo is very similar and should certainly be a contender for being made by the same hand.
There are a few others in three layer, one in the Corning, and the few sold at Sotheby's.
And those are the only pieces I have found. That is it. Of course there may well be others out there in private collections, but on the evidence so far, they are like hen's teeth.
It is possible to see many similarities between the different 'types' or 'groups' of this matt cameo, but there are so few differences that on current investigations I do not believe there were lots of people making these pieces.
I'm still waiting for two books to arrive that may have some more information in them. I'll post if they do.