Photo credit: National Trust for Scotland, Hugh Miller Museum & Birthplace Cottage
Probably by William Bonnar and painted in Edinburgh – see his sketch for the mezzotint by William and Thomas Bonnar which was published by William Bonnar on 30 October 1846 (impression in the British Museum). See: http://bit.ly/1QklbTN
The collection note they are happy for this work to be listed as 'probably' by William Bonnar (1800–1855), but can any Art Detectives find more information to confirm Bonnar as the artist?
The mezzotint is mentioned in several newspapers as ‘from the original by Wm. Bonnar, Esq. R.S.A' (i.e. Coleraine Chronicle). The earliest reference I found is from 1847 (Newcastle Guardian).
Miller’s portrait is mentioned again in an article in 1902 (Edinburgh Evening News).
About William Bonnar: according to contemporary newspapers he died on 27th January 1853 (Dundee, Perth, ... and Greenock Advertiser), not in 1855.
Yes, I don't know how the 1855 year has crept in. The correct 1853 death year is clear enough on his monument and was given in C19th biographies: https://www.flickr.com/photos/13385968@N00/17188553467
It's also right on ULAN and in Benezit (and the DNB): http://www.getty.edu/vow/ULANServlet?english=Y&find=william+bonnar&role;=&page=1&nation;=
There is a larger version of the painting in Inverness.
Another version, lent by Mrs Miller, was shown a the South Kensington Museum in 1868. This was 15 1/2 x 12 inches, about the size of the picture under discussion, but it doesn't seem to have been the same one, as the description explicitly mentions him being seated on rocks, as in the mezzotint.
A lithograph based on Bonnar's portrait, was used as the frontispiece of the first volume of "The Life and Letters of Hugh Miller" by Peter Bayne. The inscription gives his age at the time of painting as 34, thus dating it to c.1836.
The version of the portrait belonging to Mrs Miller, moreover, was on panel, while ours is on canvas.
As well as the 1846 mezzotint in the BM, (engr W&T Bonnar) and the lithograph in Bayne's 1871 'Life & Letters...' ( http://bit.ly/1Sx1bVQ ), the (American) Eclectic Magazine of March 1857 published another mezzotint (engr J Sartain): http://bit.ly/1QozuqB (preceding page 289) - a clearer image of it at the NPG: http://bit.ly/242NrnE
The 1871 American edition of 'Life & Letters...' had yet another mezzotint version as frontispiece (engr AH Ritchie): http://bit.ly/20Z8xBF ; and this one, too, looks as if it derives from the same original: http://bit.ly/1VGS7Od
It seems likely that the portrait lent to South Kensington in 1868 by Mrs Miller (doubtless Hugh's widow, Lydia, d 1876) was the original / prime / finished version, and the source for the 1846 mezzotint (and also the later prints, though they may well have been copied from the first print rather than the picture). The question is whether either of the two rougher portraits - this one at the Hugh Miller Museum and the larger one at Inverness spotted by Oliver - could be sketches or copies by Bonnar himself.
I'd have thought it unlikely Bonnar would have copied his own finished work so loosely...and why would anyone else, for that matter, have copied it so imprecisely, without even a hint of the double tree-trunk top left, for example? As for a preliminary sketch - my instinct is that this one, with its close size, looser handling, rougher blocks of paint, and slightly clumsy placing of the figure, could well be. And I'm beginning to think that the larger Inverness version makes sense too, as the artist having another bash at getting the basic composition right, together with some more detailed work on the face (which is closer to the mezzotint image than our one, especially the eyes). I wonder if any petimenti are visible on either...and anything on the back?
EDIT: the hypothesis is given a little more weight by the two related portraits by Bonner of Thomas Chalmers on Art UK - http://bit.ly/1qECjPg and http://bit.ly/1Sx82OY
The first, slightly the larger and rougher, looks like it could have been a precursor to the smoother and more detailed qualities of the second.
It does look like a sketch as Osmund suggests - there is a less likely alternative that Bonnar painted it in preparation for the mezzotint
As well as the uncomfortable squashing of the figure against the right-hand edge in this version, there are other clear changes worth noting when comparing the three images:
1. The top of the stick - significantly lower and less prominent on this work versus the Inverness one and the 1846 mezzotint.
2. The depiction of the left-hand (to us) lapel - Inverness and mezzotint pretty close, but different and rather messier in this one.
3. The check pattern of his plaid - coarser in this version, goes finer on Inverness's (though apparently not bothering to continue it over the knee), finer still in the mezzotint.
These differences strongly indicate to me a progression of concept and detail, and support the idea that this and Inverness are autograph sketches, this one being the earlier.