When a new biography of the Earl of Charlemont was published earlier in the year, this page looked at the popularity in the 18th century of the Grand Tour. Now an exhibition at Belfast's Ulster Museum explores the same subject, focusing in particular on the tour made between 1766 and 1768 by James Stewart of Killymoon, near Cookstown, Co Tyrone. Stewart's family had settled in the area a century earlier and by the time he was born in 1742 they were prosperous members of the local gentry. Both he and his father were MPs for Co Tyrone. James Stewart's mother was Eleanor King, whose family lived in Rockingham, Co Roscommon. One of the items in the Ulster Museum exhibition is a portrait of James II when Duke of York by John Greenhill; this painting originally came from the King family collection.

The centrepiece of the exhibition is a number of portraits - including one of James Stewart - by Pompeo Batoni. The son of a goldsmith, he was born in Lucca in 1708 and moved to Rome in 1727. Largely self-educated, he was originally known as a painter of religious and historical subjects; he produced an altarpiece, The Fall of Simon Magus, for the Basilica of St Peter's. However, during the 1750s he began to establish a reputation as a portraitist, and in this genre he was rivalled only by Anton Raphael Mengs. Batoni's portraits tend to share certain characteristics, not least a fondness for classical motifs, whether the use of columns in the background or pieces of statuary. There are certain baroque elements to be found too, particularly the use of swagged curtains as a dramatic backdrop for sitters.

His sense of colouring is especially brilliant - he often combines quite startling tones in a virtuoso fashion - and his ability to depict the differing textures of velvet, lace, gold thread and fur is remarkable. His subjects tend to be sharply caught and without evidence of excess flattery. Typically, the portraits of the first and second Earls of Milltown - both now in the collection of the National Gallery of Ireland - could hardly be considered kind since, despite the splendour of their surroundings and clothing, both men look distinctly unappealing. Nonetheless, for English and Irish visitors to Rome during the middle decades of the 18th century, a portrait by Batoni came to be an essential acquisition, positive proof that they had made a Grand Tour all the way to Rome. On show in the Ulster Museum is not just the James Stewart picture, but also Batoni's portraits of the second Earl of Milltown, of Alexander Stewart [of Mount Stewart, Co Down - his older brother had earlier been painted by Mengs], of Wills Hill, first Earl of Hillsborough, and, rather unusually, of Mrs James Alexander of Co Down; the artist rarely had any female sitters since women tended not to undertake a grand tour.

The Batoni portrait of James Stewart is a splendid affair, probably painted in early 1767 and showing the subject dressed in his uniform as captain of the 13th Dragoons, with which he had served prior to his travels. While his left hand, holding a hat, rests against his sword, his right hand leans on a pedestal supporting a bust of Minerva, a studio prop which the artist used in several other portraits. Also in this exhibition are a number of other fine works such as would have been collected by Grand Tourists anxious to bring back souvenirs of the places they had visited. Among these is a series of views of Rome by Giovanni Paolo Panini, a set of Piranesi's famous Roman prints and Bernardo Bellotto's View of the Arno from the Vaga Loggia from the Beit Collection, as well as works by John Robert Cozens, Joseph Wright of Derby and George Barret, all of which show how widespread an influence Roman art had at the time.

Eventually returning home in 1768 and taking his seat in parliament (which he then held for 44 years), James Stewart was to become closely associated with the Earl of Charlemont, whose chief spokesman he became in the Irish House of Commons. In 1774, he married the Hon Elizabeth Molesworth, daughter of the third Viscount Molesworth. Following the Act of Union, he became an associate of the Prince Regent and in 1803 he commissioned the prince's favourite architect, John Nash, to remodel Killymoon into a neo-Gothic castle, which is how it is still seen today.

James Stewart of Killymoon; An Irishman on the Grand Tour 1766-1768 continues at the Ulster Museum, Belfast, until Sunday, November 21st.