When were the first accurate clocks invented?
In the middle of the 17th century, the discovery of the pendulum allowed timepieces to tick at a controlled rate. Spring-driven clocks from the Renaissance were notoriously inaccurate. While they might be elaborately designed and sport a host of dials—telling the month, the day, and what religious occasion was coming up, for example—the technology did not exist for clocks to accurately track time in seconds. None of these pieces had minute hands.

Clock technology advanced significantly in the 18th century, but for most of that period, only the very wealthy could afford them. The onset of the Industrial Revolution spurred efforts to manufacture clocks more cheaply so workers could get to their jobs on time and manufacturing processes could be coordinated, and, by the middle of the 19th century, they were in most peoples’ homes. 

What sets the value of a collectible antique clock?
A combination of quality and condition is what counts. This includes the movement, the finish on the case, and how attractive the case is. Reliability also plays an important part: If a clock has been sitting unused in someone’s attic for the past 70 or 80 years, it is very hard to bring it back to a state where it will run reliably. Its value is therefore impaired. If a fine timepiece has been well maintained, it can provide hundreds of years of service.

Does it matter if the works are restored?
It depends on whether the artisan was famous and produced movements in a unique style. People began collecting clocks a century ago; prior to that, parts of even unique clocks were routinely replaced when they malfunctioned. If you are buying a precision clock by a famous maker who used a unique style, it is very important that the movement be that of the workshop.

What about clocks made by less renowned craftsmen?
In these cases, it is not as crucial. I once bought an early 18th-century English clock in a lacquer case. When I looked at the movement, I saw it was restored in about 1850. That is perfectly fine; it was an honest repair. The owners went to a competent clockmaker, and it was repaired well. A clock of that sort with all the original parts will be worth more, but they are pretty hard to come across.

How much does rarity affect value?
Many clocks are not unique, but if it is a rare piece, and in good condition, that will drive up the price. If it is an ordinary piece, the buyer can pick and choose. For example, English clocks with pagoda tops and mahogany cases were made in London from 1750 to 1790 in huge quantities. These can be acquired for a reasonable price. However, if you find one by a famous maker such as John Ellicott, who set up his London shop in the 1690s, it may set a record price.

Should you buy antique clocks at auction?
This has several drawbacks; one of the most serious is the absence of a guarantee that the clock works. In fact, all the auction house disclaimers essentially boil down to caveat emptor. They will guarantee the authenticity of the clock; if they say it is an 18th-century piece, you can rest assured that it is. However, they do not guarantee the condition. To know whether it is working or not, you need a good inspector.

Do antique clocks appreciate over time?
The value of antique timepieces may keep pace with inflation. However, timepieces are long-term investments, and they are not the most liquid assets in the world. Consider this: If you decide to liquidate your collection in the short term, you are probably going to lose a lot of money. Auction houses may charge you as much as 30 percent of the sale price. In order to make money on an investment in a fine clock, the piece must appreciate a large amount, which does not usually happen over short time frames.

What English artisans are the most sought after?
Edward John Dent is one of the best. His London-based firm, founded in 1840, actually built Big Ben. Frodsham, founded by William Frodsham and his son, Charles, around the same time in London, is another important name. They are both guarantees of quality. Fine English antique clocks like these routinely sell for over $100,000. The English are the main collectors of English clocks; they drive the market.

Who are the finest French artisans?
French clockmakers are as renowned as the English. For example, if the early 18th-century clockmaker Julien Le Roy’s name is on a clock, it is valuable; he was one of the finest clockmakers of his time and made all types of timepieces. England and France produced different styles; the French specialized in making fancy, elegant regulators, while the English ones were more massive.

What are regulators?
Regulators are tall case clocks with compensated pendulums, made from about 1725 until the 1950s. They have plain cases; mahogany was the wood of choice over oak or pine, and it was often cut and veneered with elaborate graining.  

Who built sought-after American regulators?
One of the most famous is Edward Howard, a late 19th-century artisan known as the father of American watch making. His clocks sell for more than $50,000.

How do you judge the quality of a regulator?
Good clocks come in good cases. The clock should stand securely against the wall. It should not have split wood or missing pieces. There should be no signs of abuse.

What about mantel clocks?
There is a distinction in quality of engineering between American and European mantel clocks. Many American shelf clocks from the early 19th century only run for 30 hours, so you have to wind them every single day. If I were buying a mantel clock, I would want to wind it every eight days, like a French mantel clock. The French clocks are also more elegant and better made. The 18th-century ones are made of bronze and are very elaborate, with Rococo scrolls and figures. The English mantel clocks come in black ebony veneer cases and also, typically, run for one week on a single winding.

What trophy clockmakers are people collecting?
One is Thomas Tompion, who made tall case and mantel clocks in the late 17th century. He made the clocks for the Greenwich Observatory and was recognized as the best artisan in London. His pieces fetch $100,000 and up. As for French clocks, fine bronze clockmakers like Jacques Caffiere or Jean-Joseph Saint-Germain are very popular. Those with signed cases are worth $30,000 and up.

What about American makers?
Simon Willard, who worked in the late 1700s and early 1800s, is one. A fine Willard longcase clock made of mahogany is worth over $100,000. He set up the first clock factory in America near Boston. He was the Henry Ford of his time. The clocks sold for $65, which was very expensive for that time.