His earlier landscapes were painted with a restricted range of buffs, blues and grey-browns, but he later developed a brilliancy of colour, producing works that included angular block forms.

His father, who worked in Elephant Yard off Magdalen Street as a bootmaker and an overseer of the poor, was a churchwarden at St Saviour's.

[5] In 1790, the 13-year-old John was apprenticed to Benjamin Jagger of Norwich, the leading carver, gilder, picture dealer and printmaker in the city.

[8] In 1806, when he had already established himself as a picture framer and gilder in Norwich, he described himself in the Society's catalogue as a "Miniature Painter and Drawing Master".

[11][12][13] Paintings by members of the Norwich School were framed by Thirtle, including those by Cotman, John Crome, Thomas Lound, James Sillett, and Joseph Stannard.

[11][note 3] When Thirtle framed George Vincent's oil painting Trowse Meadows, near Norwich (first exhibited in 1828), he made a watercolour version of it.

[15] His trade label took several forms, ranging from the early 'Thirtle, Miniature Painter, & Drawing Master' to the elaborate 'Carver, Gilder, Picture Frame and Looking Glass Manufacturer, Wholesale and Retail', used in the 1830s.

[17] In 1922, W. Boswell & Son acknowledged in one of their publications that "Thirtle was a well-known frame-maker, and the maker of the now famous swept frame, which has never been equalled, he also was, and still is an artist of no small repute.

During his third period, from 1813 to 1819, when his article style returned to being more conventional and less realistic, he produced outdoors what the art historian Andrew Hemingway has described as "wonderfully spontaneous and sure sketches".

After he became a landscape artist, depicting scenes of thunderstorms and the rivers Yare and Wensum, the nature of his exhibited works changed.

[28] By 1824 Thirtle was taking on pupils: he was employed by Thomas Blofield to instruct his daughter Mary Catherine and he also taught James Pattison Cockburn.

He continued to produce picture frames as well as to paint river scenes, reminiscent of the works of Peter De Wint.

This greatly interfered with his work output, although the art historian Derek Clifford has commented on the stronger and more freely expressed manner of these later drawings.

[11] His style was influenced by the English watercolourist Thomas Girtin, as well as fellow members of the Norwich School, such as Crome and Cotman.

[41][42] The large finished drawing The Boatyard, near The Cow Tower, Norwich (1812) is independent of Cotman's influence and has more naturalism, as it relies to a greater extent on carefully observed light effects.

The Times, announcing an exhibition of works by lesser known members of the Norwich School in July 1886, described him as "a good portrait painter and a charming landscapist in watercolour, his drawings being full of observation and treated with a freedom, breadth and delicacy that are really remarkable".

[43] His earlier landscapes, from 1808 to 1813, were painted mainly with a restricted range of buffs, blues and grey-browns, as exemplified by Interior of Binham Abbey (1808), now in the Ashmolean Museum, Oxford.

[38] Clifford praised Thirtle's ability to organise his subjects harmoniously in an unforced and unselfconscious way, but noted how he was less able than Crome to "give the impression of an unaffected, unselected chunk of nature".

[4] The treatise is an important document for art historians that provides documentary evidence of Thirtle's approach to his work as an artist.

[48] It consists of an unorganised collection of technical instructions and observations, possibly made from paraphrases of published works such as Ackermann's New Drawing Book (1809).

[48] It contains what Hemingway describes as "undertones of a classical aesthetic", also to be found in John Berney Crome's lecture Painting and Poetry.

[19] Thirtle used a natural indigo pigment for producing fine greys,[50] obtained from indigofera tinctoria, a species of the bean family.

[50] An example of such a work is his River Scene with laden Wherries and Figures, an undated pencil and watercolour, in which the pink glow of the sky and the sea have been unintentionally caused by the fading away of the original greyish blue colours.

To celebrate the centenary of his death, some of his works were shown in an exhibition in Norwich Castle in 1939, but it was forced to close because of the outset of the Second World War.