Oh Eugénie, how interesting! I have seen these in colours but never in cloud before.
It does look like a 283 pattern piece, doesn't it, but as far as I can see, there was no 283 ringholder made, so I am at a loss! I wonder if Chris Stewart of the Davidson / Cloud Glass site can help us? Perhaps it was a special order for one retail customer... ?
What diameter are they please? It would be useful to compare with the size of the 283 pintray which is 3" diameter (76mm).
Chris has, on his website, a number of unknown cloud glass makers, one of which made a candlestick very similar to (but a slightly different size) the Davidson 283 one... I wonder if that might be a clue? http://cloudglass.com/ndcat.htm