While working for the Duke of Dorset, Donkin consulted the engineer
John Smeaton, an acquaintance of his father, as to how he could become an engineer. At Smeaton's advice in 1792 he apprenticed himself to
John Hall in
Dartford, Kent, who had founded the Dartford Iron Works (later
J & E Hall) in 1785. Shortly after completing his apprenticeship, he set himself up in Dartford, with the support of John Hall, making moulds for paper works, for at that time all paper making was done by hand. In 1798 he married Mary Brames, daughter of Peter Brames, a neighbouring land owner and market gardener, and a prominent supporter of the Methodist movement. By doing so Donkin became brother in law to John Hall, who had married Mary's elder sister Sarah in 1791.
Fourdrinier machine In 1801–2 Donkin took a prototype of a continuous paper-making machine, and started its transformation into the famous
Fourdrinier machine which is the basis of modern paper-making. Donkin took premises at
Bermondsey, London in 1802, thus starting the enterprise that became the Bryan Donkin Company, which still continues in business in the early 21st century. In 1804 he succeeded in producing a working machine. A second, improved one, was made the following year and in 1810 eighteen of the complex machines had been erected at various mills. Although the original design was not Donkin's, he received the credit for having perfected them and brought them into use. His company continued to make such machines, and by 1851 had produced nearly 200 machines for use across the world.
Printing machinery Donkin also worked with printing machinery. In 1813 he and a printer,
Richard Mackenzie Bacon of
Norwich, obtained a patent for a "Polygonal printing machine"; this used
types placed on a rotating square or hexagonal roller or "
geometric prism". Ink was applied by a roller which rose and fell with the irregularities of the prism. One of these machines was set up for
Cambridge University. It however proved too complicated and suffered from poor inking, which prevented its success. However, it was the first machine to introduce composition ink rollers which were considered better than the existing leather-covered rollers. Donkin's inking roller quickly became the industry standard.
Tinned food Donkin became interested in
canning food in metal containers.
John Hall acquired
Peter Durand's patent in 1812 for the sum of £1000 and after various experiments, and in association with Hall and Gamble, Donkin set up a canning factory in Bermondsey, the first cannery to use
tinned iron containers. By late spring 1813 they were appointing agents on the south coast to sell preserved food to outbound ships. London's
Science Museum has an early Donkin tin can.
Difference engine During the 1820s and 1830s,
Charles Babbage requested Donkin's assistance in resolving continuing disputes between Babbage and
Joseph Clement who had been commissioned by Babbage to manufacture the difference engine. This included investigating the ownership of intellectual property, tooling and piece-parts of the
difference engine. The machine was used by
William Farr at the
General Register Office to compute
life tables, which were published in 1864. It operated on 15-digit numbers and 4th-order differences, and produced printed output just as Charles Babbage had envisaged. This machine is now in the
London Science Museum. ==Civil engineering==