yes, agree it would be very satisfying to discover the maker/s of such pieces - when you think of their importance, rarity and attractiveness, it's amazing that this information on this silvered/mercury glass remains elusive. I notice that C.H. also mentions W. LUND as a third patentee. With hindsight, do we think James Powell to have been a likely contemporary maker to whom the patentees might have offered their invention for production? - the answer is, possibly yes, and it's this 'possibly' that in some people's minds wins the day. Like another London house, Apsley Pellat, Powell was a highly respected maker at that time, and both companies no doubt had the skill to produce such material - it's just that positive proof seems hard to come by. If you read C.H. (pp. 269 - 271) you can see the difficulties involved in making silvered/mercury glass.
In view of the efforts by the patentees, to protect their invention, then do we think it's fair to say that in the U.K. this type of glass was truly new and a novelty, and not just a rehash of an earlier design? From what I can gather, U.K. glass houses in mid C19 like Powell and Pellat - more so than say the Midlands group of makers - seem to have been keen on historic designs - think of the Venetian revival and on toward Salviati and art nouveau ............ so might they have turned their noses up at novelty glass such as this, especially as it was far from easy to make? Just thinking out loud here.
Being vastly less than knowledgeable about such things, I'm not qualified to comment, but find it difficult to support the Whitefriars attribution if for no other reason than the depth of research into that maker appears to have failed to find proof - but who knows.
Generally, if you are a patentee, what is the likelihood that you will be the manufacturer also? Don't know - but it's a fairly safe bet that there's always a percentage of inventions that are related to both, but certainly being the patent holder doesn't automatically imply you are the maker as well. I know we've discussed before to what extend a British patent or Registration - in the C19 - gave design protection outside the U.K. - the answer is probably not a lot.
Coming back to Kevin's details about the auction of Michael Parkington's pieces of this glass - he did have a lot of this material and obviously purchased very wisely - maybe he had an astute and well informed adviser
- at any rate M. P. looks to have been trying to corner the market in the stuff.
My personal thoughts on the Christie's sale catalogues (two sales separated by over half a year), is that they were being economic with the truth in the matter of information regarding the family tree of this glass. From what I can see, all pieces are stated to be from either Varnish or Hale Thomson - this might lead the unwary to imagine that these companies were also the makers - but then perhaps you shouldn't be at such auction houses if you didn't know otherwise.
I might try and speak to the V. & A. and see if anything more specific can be discovered about the alleged Powell connection for this glass.