Chairs are among the most essential pieces of furniture, and not surprisingly the finest antique ones - usually those made in the 18th century or earlier - can be very valuable. In this article Early oak chairs Walnut chairs Thomas Chippendale chairs Regency chairs Windsor chairs Balloon-backed chairs Dating chairs Prices for dining chairs aren't only affected by quality and age but also by the number of chairs in the set - the longer the set, the more expensive each chair becomes. But if you choose a simple pattern you may be able to find odd numbers of chairs and build up a set piecemeal. The first chairs were simply constructed like stools, with a plank of wood at the back which sometimes had carved decoration. During the second half of the 17th century, walnut replaced oak as the favourite wood and chairs were often elaborately carved with scrolls on stretchers and legs. Mahogany chairs became popular during the 18th century, and chair styles reflected designs published by leading designers such as Chippendale, Hepplewhite and Sheraton. Their pattern books were circulated nationwide to cabinet makers, who reproduced the designs, often in much simplified form. Nowadays, when a chair is described as 'Chippendale', 'Hepplewhite' or 'Sheraton' it usually means it's based on one of their patterns rather than made by the cabinet maker himself. Early oak chairs Carving can help identify a chair's origins. The one pictured above dates from c.1640 and is carved with the dragon crest and scrolled arms typical of the Gloucestershire region. Price is from $1,700 to $8,500, depending on condition. Walnut chairs This c.1720 walnut chair has the cabriole legs and drop-in seat characteristic of chairs of the period. High-quality chairs of this date wouldn't have had stretchers, so this one was probably made by a provincial maker. Price is from $500. Thomas Chippendale chairs Many of Chippendale's chair designs featured pierced splats carved with scrolling foliage and incorporating Gothic elements, as seen on this c.1765 chair. Ribbons and chinoiserie details were also popular. Price is from $1260. Regency chairs This c.1800 painted chair, with gilded decoration, slender arms and ebonised and tapered front legs is typical of the early Regency period. Later chairs were more heavily proportioned. Price from $850 to $3,000. Windsor chairs Windsors are made from country woods such as elm, oak, ash and yew and usually date from after c.1700. Yew Windsors, such as this one, made c.1810, are the most sought after. Price from $850. Balloon-backed chairs The value of this c.1860 Victorian walnut balloon-back chair is increased by its fine proportions and desirable needlework cover. Price from $500 to $400. Dating chairs Before the 19th century, chair seat frames were strengthened with glued corner braces. After c.1840 shaped and screwed triangular brackets were used. What to look for Examine chairs carefully for signs of genuine wear and the patina of age - nearly all types have been reproduced at some time since the 19th century. If the colour of one part looks very different, it may be a replacement. Thick brown varnish often indicates a chair trying to look older than it is.