Turkish carpets are woven in four varieties: the most common and least expensive is wool on wool, which means wool pile on wool warps and wefts. Wool is thick and therefore does not allow for a very high knot count which is one of the characteristics of a valuable carpet.
Wool on cotton, which means wool pile on cotton warps and wefts allows more knots, because the cotton base can be spun finer than wool. Silk on wool or cotton, which means silk pile on warps and wefts of less expensive material is not very often found, but silk on silk (silk pile on silk warps and wefts) is definitely the Rolls Royce of carpets. Many of the carpets made from all silk have a very high knot count and should therefore not be used to cover the floor but rather as a tapestry hanging on the walls or as throws and pillows.
There are two other distinctions: carpets made from dead wool and those made from live wool. As the name indicates, dead wool stems from sheep which are already dead and has a rough and rather dull quality because it has lost its natural oils. Live wool is sheared from living animals and of much better quality.
Secondly, carpets are either hand woven, which makes them much more valuable and hence expensive, or machine woven. To tell the techniques apart one has to flip the carpet over and look at the regularity of the little squares which make up the weave. Irregularities are a sure sign of handiwork.