In it's varied forms, The ''Iron Chair'' construction could be as simple as several steel or brass straps place over a fire or related heat source. Victim's - once installed, were simply roasted alive. In other constructions, an iron armchair was fashioned. Victim's were strapped into the chair with the fire source being drawn closer and closer (for the desired effect). Spiked iron chairs, which were chairs with attached sharpened spikes - attached to the back, arms and legs of the chair. The numbers of spikes could range from 500 to 1,500. When strapped onto the device, a number of pressure restraints could be applied (singularly or collectively).
Of course, fire or coals could be placed under the chair for even more effect. Generally speaking, the placing of the spikes were such as to NOT pierce vital organs and blood loss was kept to a minimum. Death could be quick or long (depending on the skill of the executioner). IF the victim survived, the Chair - they would no doubt die from blood loss or infection to their wounds (brought about by the conditions of their cells, no doubt). The Chair was also a very effective psychologically as well. Just taking an accused to witness some other soul's torment could produce a Confession - or Recantment. During The Spanish Inquisition (1450-1600 AD), the Iron Chair or Brass Seat was a very popular device for extracting information. The use of the Chair went on well into the 18th Century.