Firstly you have two firings to put a pot through,..Biscuit ( or Bisque ) and Glaze ( or Glost ).If y are embarking on a Bisque. You MUST ensure the ware is thoroughly dry.A crude test is to offer the base of the pot to your cheek and if it feels cold it will be damp and your lovely pots will explode BOOM!!
Next, you should have a base shelf or Bottom 'Batt'. Better circulation and avoids dripping glaze spoiling the kiln structure.Always place smaller,flatter pots first so the kiln loads from smaller to the largest wares,this avoids unstable weight build up on tall 'Props' which are not always available for ginormous,awkward shaped pots any way.
Only in a Bisque firing can you touch other pots. In fact experienced potters will mostly throw their pots to a throwing gauge so you have same height and diameter pots to put 'rim on rim' and its o.k. to place other pots within pots ( don't forget they are there when you unload ! ) ) so long as they are not tight or stuck within each other. Biscuit pots are going to lose ,chemical' water and will shrink between 12% / 15%. Always use a triangular configuration of props per shelf ( a three legged table ain't gonna wobble ! ) one to the back and two to the front ( see your cones & ware through the 'spyhole then ! )
What the hell are 'cones' ? ...Well now. It's crucial you know the heat of you're kiln !!! Experienced potters can make a pretty good judgement simply by looking at the colour of the heat,! 1000o C is kinda cherry red (just short of this temperature is roughly yer biscuit temp ) , 1120o C 'orangy red and so on. If you do not have a pyrometer installed ,( a thermocouple probe within the kiln leading via compensating cable to a a read off dial outside ) then your last,and best method in my opinion, are pyrometric cones.Most commonly used ones used in this country now are known as 'Orton' cones. Best because the tell you the heat done to ware,that is , like baking a cake, a knife pushed into the cake gives you a "is it 'cooked' on the inside" evaluation rather than what the 'ambient' temperature is,often quite different from top to bottom of kiln and near & far from an element....Keeping up so far ?
Now cones come with their temperature values stamped on them. 04 =1070o C 03 =1101o C etc. You need, for bisque, 06, the closest we have to what we want ( 1011o C ) Manufacturers will tell you you need three , a waning cone , a firing cone and a 'oops' I've over fired it cone ( I wonder why ?..£££ ) two will do ,pre and actual. They say buy proper cone holders but if you carefully press them into a piece of clay at the right angle ( dictated by the cut angle at the foot of the cone ) and pierce the clay full of 'matchstick' sized holes , they will survive the firing. The idea is to place them on a shelf or prop to be visible in the kiln through the 'spyhole'. The 'pre' cone or 'warning' cone will tell you to be vigilant and give you just enough time to make a cup of tea ! then its keep an eye open for the fire cone.What they do is begin to melt on temperature.In fact a melted cone is an over fired cone. You are looking for a 'just bending' moment for utter accuracy! So your warning cone will indeed melt flat and you must catch the fire cone at that 'wilt' stage and turn the kiln off !!! or you re going to at best over fire it and at worst have a complete meltdown if you forget it and go to bed! (Yep, I've done it once and believe me EVERYTHING can and does melt given enough heat til the elements give up ) There is a slightly different procedure from this point with a glost kiln,more on that another time.
The bit I haven't given you yet is how do you get the heat up to your desired temperature ?
If you have a small simple kiln there is usually at least one 'Sunvic' dial or temperature controller. This is usually marked in % or 'low' 'med' 'high' Biscuit must not exceed a temperature clime, of say 100oC an hour! ( or 'boom' again ) This allows the 'chemical water' to leave the pot safely. Vere on the side of safety and rather fire a bisque slower than too fast. Some potters if presented with a kiln loaded with large pots will pre fire 'low' over night then up it the next day. Usually its enough to turn the dial to low for a couple or three hours then med for the same time and finally high until top temp.I have % on my Sunvic and have a regime of an hour each on 25% 45% 65% 80% 100%. YOU MUST keep the bung brick out until at least cherry red to let the boiled off water to escape the kiln then replace it.Another trick here is to hold a mirror close to the open bung or spy hole and if it steams up with water leave it open to continue steaming.
Finally leave you kiln to cool for at least as many hours as it took to fire up.Very roughly 9 to 14 hours according to size of kiln and wares and then only remove bung fist for an hour or so Then 'chinck' the door a tweak ( vital not to cause a draught , particularly on glazed pots ! ) and slowly build up opening the door in increments.If you had a pyro, this would never be before 300oC.( domestic ovens are around 200oC top for perspective )
CONGRATULATIONS you now have perfect biscuit pots ( course you have ! )
