Other possible catalogue artists
There is only one other possible artist known about at the present time and this is W.S. Tomkin. He worked for Pitt-Rivers from around 1882 until 1890. He was employed as a sub-assistant and earned £84 per annum. Thompson and Renfrew suggest that he might have contributed to volume 2, though he is not named and did not sign the book to confirm this. Thompson says of him
The most interesting [assistant] in many ways was Tomkin, who has left us those charming drawings of Pitt-Rivers acting as scale when he was on tours of inspection. He was evidently a skilled draughtsman and the accounts show that he was sent on courses at the Polytechnic in London in 1889 for photography and drawing. Perhaps this was where he made the contacts that secured him a job with a printing house soon after'. [Thompson, 1977: 95]
His background is unknown although he appears to have specialised in producing maritime artwork after he left Pitt-Rivers' employment.  His full name appears to have been William Stephen Tomkin and his dates 1861-1940:
... William Stephen Tomkin (1861-1940) British). Tomkin was a highly proficient watercolour painter of marine subjects. He initially worked as a draughtsman for General Pitt Rivers, who was Inspector of Ancient Monuments. Tomkin exhibited "Wind Against Tide" at the Royal Academy in 1909. ... British Old barges signed and dated 'W.S. Tomkin 1925', watercolour over pencil ...
Several of his maritime works were sold by Bonhams on 14 September 2004
He prepared some of the drawings in Pitt-Rivers' private publications on Excavations on Cranborne Chase etc. [Pitt-Rivers 1892, xv] He had to redraw both skulls and coins for the first Cranborne Chase volume because Pitt-Rivers was not happy with the accuracy of his first attempt. [Bowden, 1991: 104]
He left Pitt-Rivers' employment a year after his photographic training and went to work for Waterlow Brothers Ltd. Bowden suggests that he was forced to leave the General's employment because he could 'not afford to marry on the 'pittance' he was paid'. [Bowden, 1991: 106]
It would appear from the contents of his notes, given in their entirety below, that Tomkin was learning not only to photograph outside during the ancient monument inspections, but also to photograph objects. This, therefore, gives us a brief insight into the techniques employed. Although it is extremely unlikely that Tomkin was the one to produce the photographs used in the catalogue of the second collection, presumably that photographer used roughly the same techniques.
It is also not clear exactly where Tomkin was taught except it was in London and known as the "Polytechnic".
Bibliography for this article
Bowden, Mark 1991. Pitt Rivers: The Life and Archaeological Work of Lieutenant-General Augustus Henry Lane Fox Pitt Rivers, Cambridge: Cambridge University Press.
Thompson, Michael and Colin Renfrew. 1999. ‘The catalogues of the Pitt-Rivers Museum, Farnham, Dorset’ Antiquity vol. 73 (no. 280) pp. 377-392
Thompson, M.W. 1977 General Pitt-Rivers Moonraker Press
AP, 2010, updated February 2012.