The most technically renowned pocket watch by Derek Pratt (1938-2009) is perhaps the Double-Wheel Remontoir Tourbillon, with which he found an ingeniously simple solution to implement George Daniels’ independent double wheel escapement within a tourbillon watch using a single gear train. It was the only timepiece made under his own name and the watch he entered in the 1997 Prix Abraham-Louis Breguet. However, his magnum opus is widely considered to be the unusual and exceedingly beautiful oval pocket watch he produced for Urban Jürgensen.

Nominally known as the Oval, it features a one-minute tourbillon with a cage-mounted remontoir, a spring detent chronometer escapement, a thermometer, moon phase, and power reserve indicator. Pratt had worked on the watch from 1982 until 2004, when life ultimately intervened, prompting him to entrust the piece to Kari Voutilainen, who brought it to completion.

The Oval embodies the full extent of Pratt’s expertise as an engine-turner, craftsman and watchmaker. Parallels have been drawn between Pratt and Daniels, and with just cause. Like Daniels, he embodied the archetype of the watchmaker of old, a role requiring a command over each aspect of watchmaking. This meant not only excelling in restoration, where his precision and finesse were widely admired, but also possessing the ability to construct a timepiece entirely by hand, from the ground up. Chronometry lay at the heart of his work but he also cultivated a certain mechanical elegance that was notable in itself, particularly with the Oval watch, which distinguished it from mere technical feats.

Long held in the private collection of Dr. Helmut Crott – a distinguished collector, friend of Pratt, and former owner of Urban Jürgensen – the Oval is making its auction debut on November 8 as part of Phillips’ Reloaded: The Rebirth of Mechanical Watchmaking, 1980-1999 Geneva sale.

The Watchmaker

Pratt was not only a close friend but a vital horological confidant to Daniels. Their long Sunday phone calls were filled with exchanges of ideas and insights, where Daniels often turned to Pratt for advice on his innovations. Pratt also produced components for him, including the combined wheel and pinion in the ultra-thin version of the Co-Axial escapement. Daniels later recounted in the Horological Journal, “Derek’s understanding of escapements was of great assistance to me. He immediately saw the benefit of the co-axial escapement and enthusiastically accompanied me in visiting factories to discuss its worth. He could speak French and Swiss German fluently, which was essential to our needs. We would take to the road early in the morning with coffee (and some brandy to relieve the cold) and spend the day discussing escapements with largely uncomprehending R&D departments.”

Pratt was born in Petts Wood, near Orpington in southeast London. From a young age, he enjoyed visiting the National Maritime Museum in Greenwich, where all four surviving examples of Harrison’s history-making marine chronometers were housed including the H4, which Pratt would later undertake the monumental task of replicating. He attended Beckenham Technical School and, after graduating in 1953, began an apprenticeship at Smiths Industries. In 1956, he enrolled in a three-year course at the National College of Horology but left early without completing when the final year project of creating a pocket watch was abruptly changed.

As the watchmaking college closed a year later, Pratt joined the micro-engineering firm of its former director. His work eventually led him to Switzerland in 1965, where he settled and established his own workshop in 1972. Here, he began specialising in restoration work and became acquainted with Peter Baumberger, who was a prolific collector. Pratt restored numerous exceptional historical pocket watches from Baumberger’s collection, including the most complicated Vacheron Constantin of the time, the grand complication No. 402833, made for King Fuad I of Egypt in 1929. Eventually when Baumberger acquired the rights to Urban Jürgensen in 1979, he brought Derek on board as a consultant and technical director. Pratt was thus responsible for the company’s greatest technical achievements, including the first cage-mounted remontoir in a tourbillon watch. He completed around 34 pocket watches for the company, among which 12 were equipped with tourbillons, including the Oval.

The Oval

In an April 1993 article in the Horological Journal, Pratt explained the inspiration for his oval watch, recalling a childhood fascination with oval tins that sparked his early interest in oval timepieces. This curiosity deepened when he encountered the historic oval Breguet No. 1682/4761, produced in 1822 for Count Nikita Petrovich Panin and later owned by the pianist Arthur Rubinstein. Moved by this example, Pratt felt inspired to create an oval watch of his own, describing it as an homage to some of the most preeminent watchmakers of all time like Abraham-Louis Breguet, John Arnold, and Professor Alfred Helwig.

Work on the Oval began in a time when quartz dominated horology. By then, the ranks of watchmaking houses located in the Swiss Jura had thinned considerably, leaving behind entire stocks of machinery that could now be purchased for scrap. Pratt was able to amass the tools and equipment he needed for each specific task, including rose and straight-line engines.

He was an outstanding engine-turner who created and sharpened his own tools and made his own pattern bars. He made many beautiful guilloche dials for Urban Jürgensen including those of wristwatches and made every part of the dial himself. While the movement of the Oval was entirely undecorated when he handed the watch over to Kari Voutilainen, the dial, on the other hand, was engine-turned by Pratt himself.

Made of solid silver, the dial is extremely fine, a testament to the singularity of his craft. There are different patterns incorporated into the master pattern to delineate the various displays. The periphery features a barleycorn pattern, executed with a rose engine. As the workpiece is rotated in a circular motion, it is worth considering how engine-turning is accomplished on an oval dial.

Joshua Shapiro sheds light on this process, explaining, “On the rose engine machine there is a special attachment called an elliptical chuck or oval chuck. There is a debate amongst engine turners whether it’s a true oval or not. Regardless, the chuck ovalizes a circle and can even ovalize so far as to create a straight line. It’s pretty mesmerizing to watch in action.”

“What Derek did isn’t easy.” He continues, “he had to perfectly match the oval shape to the shape of what the case would be. His guilloche work was unmatched and is my number one inspiration.”

The central portion of the dial features a straight-line diamond pattern while the moon phase and the small seconds sub-dials are decorated with a basketweave pattern, which is the most difficult to execute.

The dial is traditionally finished using a method known as Breguet frosting, a form of depletion gilding. This process involves gently heating the dial over an open flame, forming a thin layer of silver oxide on the surface. After each heating, the oxide layer is carefully removed, and the cycle is repeated multiple times. This iterative treatment gradually eliminates impurities in the silver, resulting in a pristine, pure white surface.

The numerals and markers on the brushed chapter rings and fan-shaped scales are hand-engraved and filled with black lacquer. On the left at 10 o’clock is the power reserve indicator and on the right at 2 is the thermometer. Like Breguet’s pocket watches that incorporated thermometers, there is a bimetallic strip mounted on the edge of the movement that expands and contracts. As it moves back and forth, it causes the thermometer’s hand to traverse the sector on the dial.

Pratt faced numerous unique challenges in constructing his oval watch, yet he approached each with the same determination that defined his career. The case is as technically impressive as it is visually striking. The watch is currently cased in platinum, but there was a total of three cases made for it, including one in silver and one in rose gold. The platinum and rose gold cases were produced between 2005 and 2006 by Bruno Affolter, a master casemaker at Les Artisans Boîtiers. However, the silver case, which accompanies the watch, was entirely crafted by Pratt himself using his lathe. The case consists of a bezel, middle, back, and back cover. They were turned by hand on a lathe, which like engine-turning an oval dial, required a special attachment.

As for the crystal, Pratt took matters into his own hands when he was unable to find a manufacture willing to produce large form crystals, as it required custom tooling and techniques. He eventually achieved the precision and quality he needed after multiple attempts.

The Movement

Both the dial and movement are characterised by remarkable clarity – a deceptive simplicity. The movement in the Oval isn’t just incredibly inventive but also astoundingly elegant. It’s interesting to note that Pratt produced various keyless pocket watches including the Double-Wheel Remontoir Tourbillon, but this in particular is wound by a key. Presumably, this choice was made to achieve a cleaner layout, allowing him the freedom to focus on aesthetics.

Viewed on the bridge side, the movement has a linear composition comprising of three circles – the mainspring barrel at 12, followed by the centre wheel, which is supported by a rounded and polished bridge with the hand-setting square, and the massive tourbillon at six. The third wheel is hidden on the dial side while the tourbillon is cantilevered – flying – resulting in a minimalist appearance overall. On the left of the barrel is a differential screw mechanism for the power reserve indicator. It comprises of a cone that is driven up the threads of a vertical screw when wound and as it rises, it pushes a feeler arm aside which through a driving rack (located on the dial side), turns the indicator hand through the sector on the dial.

The winding square is located on the right of the barrel in an intermediate wheel. It drives another transmission wheel on the dial side which in turn mates with the ratchet wheel. This is unusual as the mainspring is wound directly in most key-wound watches with a single barrel. The decision to route the winding through intermediate wheels was made to achieve symmetry. On the barrel ratchet on the dial side of the movement, there’s a Maltese cross stopwork fastened to it. As its name implies, it stops the barrel from winding and unwinding completely to keep the mainspring operating within its optimal tension range.

The pièce de resistance is no doubt the extraordinary flying tourbillon with a carriage-mounted remontoir. Pratt was the first watchmaker to embed a remontoir within the tourbillon cage. A remontoir is typically located along the gear train before the escape wheel and provides a small amount of stored energy that is released periodically to regulate the force reaching the escapement.

A downside to this is that the remontoir spring has to overcome the inertia of the subsequent wheels and in the case of a tourbillon, this includes the load of the cage. Thus it doesn’t completely isolate the escapement from inconsistencies in the going train. The solution then is to incorporate the remontoir on the escape wheel itself. Naturally, this is an enormously delicate undertaking as the rapid bursts of energy could transmit a disturbance to the balance and hairspring as the remontoir is released, requiring incredibly tight tolerances and great care in assembly and adjustment.

The remontoir mechanism consists of a remontoir stop wheel with three teeth, a coil spring, a fork and locking anchor as well as a cam in the shape of Reuleaux triangle. Arguably the most elegant form of remontoir, this mechanism was invented by Robert Gafner, an instructor at the La Chaux-de-Fonds watchmaking school in the 1940s.

Derek took a particular interest in the Reuleaux triangle, a shape of constant width, meaning that the distance between two parallel lines tangent to its boundary is the same regardless of its orientation. This property is unique to only a few shapes beyond the circle. Despite its triangular appearance, it behaves like a circle in terms of its width, which means it can rotate within a square, or other confining shape of matching width, without changing orientation. In the remontoir, it is used to convert rotary motion into linear motion, which controls the release of the stop wheel.

The Reuleaux triangle is made of synthetic ruby and revolves within a two-pronged fork that oscillates as the triangle rotates. This back-and-forth motion is mirrored by the remontoir anchor, to which the fork is attached. As the fork moves, the anchor unlocks one of the three teeth on the remontoir stop wheel. Each time the remontoir stop wheel, driven by the cage, snaps forward, it tensions the remontoir spring. The spring stores enough of energy to drive the escapement and thus the balance. The stop wheel advances once per second, making this a one-second remontoir, enabling it to drive a deadbeat hand.

The subtleties of the setup are incredibly ingenious. This configuration is possible as the remontoir wheel and escape wheel are co-axially aligned but the escape wheel is pivotably mounted meaning it is attached to the remontoir staff but is loose. Thus the barrel powers the tourbillon while stored energy in the remontoir powers the escapement and balance. This effectively isolates the escapement from the wheel train and tourbillon and ensures that power delivered to the balance wheel is consistent and direct.

It is truly direct as the escapement is a spring detent escapement in which impulse is transmitted directly to the balance wheel roller once every oscillation, eliminating the need for lubrication. After which, it is locked by a pallet jewel, leaving the balance free during its supplementary arc. For these reasons, detent escapements are vastly superior to the Swiss lever escapement in static or controlled positions. The detent is fixed to a lower cage bridge beneath a bridge that supports the remontoir and escape wheel.

The balance is free-sprung with four adjustment screws and has a beat rate of 14,400 vph. It is attached to an eminently traditional Elinvar hairspring with a Breguet overcoil and Grossmann inner curve for better isochronism. Kari Voutilainen applied the full vocabulary of finishing techniques to the movement, including black-polished steelwork, stripes, frosting and snailing. The result is stunning, and its effects put a spotlight on the elegance of the movement.

The pursuit of every line of inquiry in a single watch has yielded a creation beyond the reach of any superlative. From a perspective of craft on all levels of the timepiece, to the unique combination and configuration of mechanisms, to the sheer elegance in execution and its striking form, it is a physical narrative of both exploration and mastery, the culmination of a journey by one of the 20th century’s most brilliant horologists.

The Oval carries an estimate in excess of CHF 1,000,000.