It was with interest that I read the recent article in Current Archaeology ‘Experimental Archaeologists Build a 14th-Century Kiln’ (CA No.235, P.7). As a professional potter and, dare I say it, ‘experimental archaeologist’ (Maybe I need a new job title!) I am delighted to see archaeology students getting to grips with ancient technology and impressed by the well built kiln shown in the photographs. But .... somewhat astonished by the timber consumption of three tonnes which is reported. In illustration 3 (not shown here for copyright reasons) the fireboxes are shown completely choked with charcoal and ash, a situation which would certainly limit or prevent temperature rise. Unlike some other heat based technologies kilns require a little and often policy when it comes to stoking, regular removal of ash build up and strict control of air flow to encourage fast ignition of the fuel.
A clean burning firebox in my kiln at Segedunum
It is also quite apparent that the walls of the structure are remarkably low, not a problem in a clamp type tile kiln where the tiles are stacked within, and well above these ‘proto walls’ which are then extended upwards as temporary daub insulation. In the illustration the chamber is not even filled to the height of the walls making it a remarkably inefficient load; fully loaded kilns fire far more efficiently than half empty ones. The top of the tile pack is apparently not capped as it would have been, again with wasters and temporary insulation. All of these factors will adversely affect the firing of the kiln.
Temporary daub dome being removed from Segedunum Kiln
The fuel itself must be completely dry; long term, managed storage of timber is something that wood firing potters accept as part of the process. Finishing of firings would often involve the use of very fast combustibles such as dried gorse (hell on the hands but great for raising temperature).
The thing that has to be borne in mind is that the people who fired these kilns had almost certainly been doing it all their lives and had learned the skills from their parents and grandparents. I have been firing wood kilns all my potting life and still acknowledge that I have a lot to learn about the process.
If this was the first firing of this kiln its firing characteristics would have been quite different to those of subsequent firings There is a risk that calculations for large scale ceramic industries are based on experiments like this one, giving a very distorted view of fuel use, manpower requirements, land usage, etc., etc.
The Norton kiln could certainly be fired on a lot less timber. I regularly fire an experimental La Tène-derived, surface built, updraft kiln of turf and clay construction, and even though this is a Romano-British kiln the firing characteristics of which are similar to this type of kiln. Its chamber would happily accommodate something in the region of 200+ Medieval tiles and yet it uses less than 150kg of timber to reach 1000 degrees C over a period of 6 to 8 hours depending on weather conditions. That is only about 5% of the fuel consumption recorded for the Norton Kiln, even given kiln differences and a margin for error it's difficult to see how you'd get up to 3 tonnes.
I’m not saying don’t experiment, in fact I’d like to see much more experimentation. What I am saying is; if you experiment with ancient technologies seek out the best expertise you can find. I love working with archaeologists and by working together we can get great results that combine the best aspects of both disciplines.