Kilns – Or, as I have heard it pronounced all my life, “Kills”, come in all sizes and types and the burning ,or, as you call it, “firing”, of clay items goes back thousands of years – pottery shards have been found in the Ynchanyan cave in China that date back over 9,000 years. It probably started with cave men – and women - sitting around a fire that had been built on clay soil and noting that the soil was very hard where the fire had been.  Over time, they learned that this soil would stick together when wet and simple things could be made from it and if these items were allowed to dry and then placed in the fire they, too, would become hard.  Maybe a basket, woven from reeds or grapevines and then having had clay smeared on the inside so seeds would not fall through the cracks, had fallen into the fire and after the reeds or grapevines had burned away, a hard vessel remained. As time and man progressed the kiln evolved from this simple burning of items in a camp fire to what we have today. Maybe they went from a campfire to just stacking items up and then building the fire over them but more probably the campfire became a pit with the clay items placed on the bottom and the fire built on top - a very common way of burning found in many parts of the world even today.  It was found that the temperature in the pit would become higher than what could be obtained with the camp fire and that the items burned in this way would be harder and not be as easily broken.  Somewhere along the way it was found that if the temperature was high enough the ashes from the fire would react with the clay and a pot would come out with a slick shine to parts of it.  Over time, they found that pots burned like this would hold water and the race for an ever hotter burning kiln was on. Variations in design evolved into what we know as the groundhog or shotgun kilns used here in the US even today with the fire at one end of an enclosed rectangle and a chimney at the other. It was found that if they build a kiln into a bank with the fire placed at the bottom and a hole at the top for the smoke and heat to escape, a draft could be created which would increase the temperature markedly.  Further refinement produced a kiln built up the hill with several chambers which allowed for better control of the temperature.  In more modern times, a downdraft design was developed in which the fireboxes were along the sides of the kiln and the heat came up the inside and then down through the ware and out the chimney, allowing for more control and even temperatures inside. In modern times, better insulating products and designs have given us the highly efficient kilns of today.  They come in all sizes from those used by studio potters to the tunnel or continuous kilns used in industry.  They are used for everything from drying lumber to making jewellery to smelting metal to burning bricks, garden pottery, dishes and many industrial uses. OK, but what is a kiln? In its simplest definition, it is nothing but a container that holds heat – the more heat input vs the heat lost equals a rise in the inside temperature.  (Much like our bodies – more calories in vs less calories out and we gain weight.  :) The fuel used to produce the heat can be anything that burns or produces heat – from wood, coal, petroleum produces like fuel oil and natural gas to electrical heating elements. All of us are familiar with the kilns used by studio potters today - the most common being the electric kiln which uses a type wire that will withstand high temperatures that are wound into coils or “elements”.  As the electrical current goes through the wire, the resistance causes the wire to heat to very high temperatures.  These coils – or elements – are normally placed around the insides of the kiln and with no exit for the heat to escape very high temperatures can be obtained inside the “container”.    In years gone by, hard firebrick or even the earth itself was used to build or line kilns but today soft firebrick and the newer “fiber” materials that have come from the space industry are most commonly used.  This makes the kilns lighter and gives them a high degree of insulating or “R” value, thereby allowing for a higher temperature and more economical operation.
BROWN’S POTTERY - from the inside