In order to learn the art of painting on glass he gave up the hosiery business, but about 1748 accepted a situation as purser's clerk to three ships belonging to the East India Company.

After an adventure with some French men-of-war at Tellicherry, he made a long overland journey with a small company of Indians, adopted a form of local dress and let his beard grow.

Herbert sold his business and stock to Henry Gregory for a thousand guineas, and retired to a country house at Cheshunt, Hertfordshire.

After the death of his second wife he married Philippa, daughter of John Croshold, mayor of Norwich, and niece of Robert Marsham of Stratton Strawless, Norfolk, who also brought him a good fortune.

Herbert, who calls himself ‘hydrographer,’ states in the dedication to the East India Company, ‘all that has been set forth in the Neptune Oriental has been carefully examined and compared with the particular remarks and journals of ships in your honour's service, as also some country ones, besides many curious charts and plans I have been favoured with, as well as many collected whilst I was in India.’ A second and third edition, unaltered, were issued.

Joseph Ames's interleaved copy of his Typographical Antiquities, with the plates, blocks, and copyright, came into Herbert's possession, and in 1780 he issued proposals for a new edition, upon which he had then been engaged twenty years.

He searched the registers of the Company of Stationers, worked in public and private libraries of the kingdom, and carried on correspondence with owners of rare books.