The Auckland Studio Potters in 2000 decided to build a new salt kiln. The previous salt kilns were diesel powered and were of modest size (about 8 cuft). Because they had an existing wood fired soda kiln and had a ready supply of free wood, it was decided that another wood kiln of similar chamber size would be most useful. Another reason behind the choice of wood as a fuel was the belief that it produced the richest salted surfaces and that the kiln design could lead to an excellent salting bed.

The existing wood kiln was of a Phoenix fast fire design and our experiences of firing it informed our ideas about the new wood kiln. So we went for a Bourry box style firebox, joined to a chamber of about 30 cuft and a tall chimney. We reasoned that the Bourry firebox was a good heat producer, provided an excellent ember bed for salting and would be relatively easy for students to stoke.

Plans were drawn up that were based on existing kiln plans published in various books and magazines and adjusted to fit our stock of kiln shelves. The construction of the kiln took the proverbial month of Sundays as the members of the ASP only built the kiln for 3 hours per week on Saturday mornings for about 3 months. However it provided the membership with valuable knowledge and kiln building skills. All of the bricks used were second, third or forth hand from other kilns and required a fair amount of cleaning. For the chamber arch the ASP splashed out and bought new arch bricks.

The new kiln was fired by both members of the society and students, with some very beautiful results. One hoped for aspect of the design, that of easy stoking, proved not to be the case and there were a few extremely long firings due mainly to inexperience in stoking, or wood preparation.

In early 2002 it was decided that the firebox and throat needed an overhaul, as some of the firings were taking too long and the results were less than satisfactory. Many of the problems stemmed from the ember bed getting too large and choking the throat. Another problem was the difficulty of cleaning the firebox after each firing; the wood burnt was from demolished pallets and contained a lot of nails. We were also suspicious of the firebox arch – it appeared to be slowly collapsing due to insufficient bracing.

So the decision was made to partially demolish the firebox, enlarge the throat and re-brick the firebox roof. The firebox throat was enlarged by 184%, this would make the ember bed less of a problem and also allowed easier access to clean the firebox from the chamber side as well as the firebox entrance. The hobs and mouse hole arrangement remained unchanged as did the primary air intakes once the roof was re - bricked.

These changes reduced the average firing from around the 16 hour mark to 14 hours and made the ember bed management much easier. Previously the stoking required careful attention to the placement, amount and condition of the wood. This meant that for the inexperienced stoker or those new to this style of kiln the learning curve lengthened the firing, sometimes considerably. The new throat helped in that if the stoking pattern produced too many embers there was more time to adjust and correct before the throat would become restricted.

After several firings however a new problem became obvious and was the result of the difficulty of inserting an arch into an existing weight bearing wall. The portion of the wall above the new throat was slowly settling downward each firing, flattening the throat arch and causing stress on the main chamber arch. This, combined with the firebox arch still exerting sideways pressure, meant that another solution to the throat was needed. Also around this time the wood supply changed to free mill slab – not a nail in sight. This meant that the mouse hole air arrangement could be altered.

So again the firebox was altered. This time it was completely demolished and three throats were inserted, spaced evenly across the kiln. Each throat now had a corbelled arch, which is a lot easier to insert and more structurally sound in the situation. The overall throat area was approximately the same, just spread out. The firebox entrance was modified to align with the new throats and a new double grate system was introduced. This means that in addition to the hobs as usual in their normal position, below them there is a grate, four and a half inches off the floor, constructed of firebrick and similar to a dutch oven grate. This allows for very efficient control of the ember bed, so that even if the wood is a bit damp or green, complete combustion is possible within a useful time frame. This new grate was combined with an overall reduction in height of the firebox (affecting only the area above the hobs), straightening the outer firebox wall and using kiln shelves to top off the firebox as opposed to an arch. All these alterations have been beneficial and reduced the firing times, now down to 12 hours approximately.

In 2004 the kiln was being used less and less, partly because the students were preferring the easier (but considerably smaller) gas fired salt kiln and also many of the keenest wood firers were occupied with building and firing the Anagama kiln. So it was decided to try a novel solution to make firing easier, more reliable and faster – diesel. The ASP had inherited a couple of very fine Twiss burners and so these were used in conjunction with wood. The idea was to fire with wood until the bag wall was about 1000 degrees, then turn the Twiss jet burners on, firing across the firebox, through the throats and hitting the bag wall. The wood stoking continued in a much-reduced fashion and kept the firebox hot and ensured a good flame in the chamber and complete combustion of the diesel. The first test run had the diesel on too hard and collapsed the bag wall and badly melted two throats, so another throat rebuild was needed to slightly enlarge the outer two throats and replace the bricks with high grade refractories. The floor and bag wall was also rebuilt. Since then it has been fired very successfully a number of times, with an almost guaranteed 12.5 hours to flatten cone 11 and the ember bed is still very good to throw salt on.