With cheaper chess sets, the pieces are easily pushed over with a light brush of the finger past the piece which can easily upset the whole board layout. So with better pieces such as these from Google: http://www.google.co.uk/products?hl=en&rls=GGLJ,GGLJ:2006-33,GGLJ:en&um=1&authorid=1104921&cdn=ChessBaron+Chess+Set&q=&scoring=pd
– heavy alloy is added to the hewn out base which gives it bottom weighting and subsequent on-board stability. Triple weighting is a mark of a good chess set but there are other factors to look for too. But be wary – no chess set is worth over 1000 GBP or so. It’s all profit margin justified by some special stamp or authentication device. A good alternative is these pieces which are the same as Jaques sets and are from the same supplier as Jaques: chessbaron.co.uk/chess-X2016.htm. Start with looking for triple weighted chess pieces and look also for quality wood such as ebony and budrose (or bud rosewood) – the extra cost is well worthwhile.