Boat Passing a Lock is an oil painting by English artist John Constable, depicting a boat approaching Flatford Lock, close to the mill owned by his father. The design of the lock used at the time, called a flash lock or staunch gate, is different to those used today, with only a single gate, which could be opened releasing a rush of water upon which a boat upstream of the lock would be carried down in a rush. To move a boat upstream the gate was opened, and the boat was winched up, before closing the gate to achieve a flat stretch of river along which the boat could be rowed, punted, or towed more easily. These locks were first used in Europe during the Roman Empire, and were in use in England by at least 1265.
Flash locks were often built into dams or weirs associated with mills, such as the one owned by Constable's father, and were clearly better suited to carrying laden vessels downstream and unladen vessels upstream; for much of England's history this would have meant carrying agricultural products downstream towards larger market towns or ports; from Dedham this would have meant Manningtree, Harwich, and Felixstowe.
The Industrial Revolution created the need for a more flexible system, raw materials moving upstream to manufacturing towns and manufactured goods being shipped back towards ports, leading to the adoption of pound locks, which have two gates, and the water in the area between is raised or lowered by opening flaps on the gates, creating a flat expanse of water on either side of the lock, and allowing boats to proceed easily in either direction. Pound locks first appeared in China during the Song Dynasty (960-1279), with their invention being attributed to the naval engineer Qiao Weiyue in 984. A pound lock was invented separately in the Netherlands in 1373, with examples appearing in Belgium and Italy shortly after.
In 1705 an Act of Parliament was passed declaring that the River Stour should be made navigable leading to the construction of a series of flash locks being built on the river, with Flatford Lock being constructed in 1708. The original lock was turf-sided, and the banks were prone to being pushed in when the gate was opened; a problem with all early locks on the River Stour, which were built without balancing beams to counterbalance the weight of the gates. The problem came about because the original Act of Parliament omitted to make provision for this, so that the tow paths were not wide enough to allow provision for such a beam without infringing on the rights of local landowners. This led to the locks deteriorating more rapidly than in other parts of the country, and a system of lintels being put in place to remedy the problem. The turf lock at Flatford was replaced with a wooden one in 1776, although this still needed lintels, with more being added over time to stabilise the structure. The Flatford Lock had nine separate lintels by 1814, although these were generally omitted from his scenes of the area by Constable because they interfered with the line of sight - in this instance removing the lintels made Dedham Church visible in the background of the image. The lintels can be seen in a painting of the same lock by John Dunthorne made in 1815.
The lock was designed to accommodate two Stour lighters, a type of cargo boat which could carry 13 tons, with two such boats being towed by a single horse, for a total of 26 tons. The cargo carried by these boats was typically either flour or bricks from factories in Sudbury, which were mostly shipped on from Harwich and Felixtowe to London. On their return trips the lighters would bring sewage from London to spread on the fields, as well as coal from Newcastle to be used in the brick factories of Sudbury.
The flash lock at Flatford was replaced with a wooden pound lock in 1838, in a slightly different position (to allow the flash lock to work while the pound lock was being built), and this was in turn replaced by a concrete lock in 1926 (the lintels, though no longer needed, were retained to preserve the character of the lock).
Boat Passing a Lock was the last of a series of large paintings of the area around Flatford painted by Constable, and was exhibited at the Royal Academy Summer Show in 1824, being sold on the first day of the exhibition for 150 guineas to James Morrison, an inn-keeper's son from Balham Hill, London. The painting remained in the hands of the Morrison family until 1990, when it was acquired by Baron Hans Heinrich Thyssen-Bornemisza for £10 780 000, the highest sum ever paid for an English painting at that time. The painting was placed on display in the Museo Thyssen-Bornemisza in Madrid, Spain, until 2012, when the Baron's widow, María del Carmen Rosario Soledad Cervera y Fernández de la Guerra, sold it to an undisclosed buyer for £22 441 250.
