Phoenix wood firing (cone 6 from raw)

To experiment some more with firing from raw, we did a cone 6 firing with the Phoenix kiln. This was my first firing as a kiln master – very much the first of many to come so I learn to fire the kiln on my own.

Many glaze tests went in as well – our first raw glazes: tests on BRT clay and on stoneware (Elisabeth Street clay).

20130823_100552

Here some pictures from the firing:

I searched the web but could not find very much information on firing schedules so here is the one that we used:

Prep:

  • We used broken-up wooden pallets -> resulting in thicker and thinner planks of wood about 1.2m length
  • get pyrometer – check battery!
  • take a warm blanket and a chair for the morning (plus all the other useful things one needs)

Phase 1: 50°C /hour to 300 °C

  • Start nice and early (5am was good, earlier would be possible) with kindling in the middle slot
  • 2 people are enough if ½ the wood is already broken up
  • Candle firing the evening before might shorten this first phase
  • Three thin planks of wood in each slot (when 2 are half in start a third one), vertically
  • Make sure ember-bed is nicely distributed to the end of the slots
  • towards the end of the phase: lots of riddling, we started to put charcoal from bottom slots to top grate

Phase 2: 100°C/hour to 600 °C

  • Ensure continuity from phase 1 (having people overlapping instead of taking turns)
  • Careful when starting wood on grate -> temp jumps up quite quickly
  • Close bottom slots to preserve ember bed (first one stone in each slot, then 2 to close)
  • Criss-cross 2 or more long logs, half in, pull out of necessary, push in when drop in temp
  • Develop rhythm -> wait 20 sec after each action to the reaction
  • Careful firing as the kiln reacts to the new wood and temps are spiking
  • Never throw plank in completely, always leave part hanging out to be able to pull out
  • Pick wood before you need it (in hand or lay next to kiln)
  • Use long pieces, keep smaller ones for the end

Phase 3 -1: 150°C/hour (before reduction) to 900°C

  • Continue from phase 2 – just a bit faster firing
  • Aim for oxidized firing in this phase
  • It was unclear how to identify 900°C: use cones or move pyrometer to a better spot?
  • Need to learn reading the temp from colours and other signs
  • When is the right temp for reduction reached in the kiln?

Phase 3-2:  (reduction) 900 to 1050°C

  • Close fire grate (to 3×3 bricks open)
  • Open passive dampers in chimney
  • Fire to the smoke (piece in, wait for black smoke to clear, then another piece -> smoke means that there is reduction happening)
  • Stop when cone 05 is over – about 1040
  • May take up to 2 hours
  • Put the stones for the dampers somewhere where they can be found again 😉

Phase 3-3: 150°C/hour (after reduction to cone 6 over)

  • Close passive dampers
  • Look at smoke (to prevent from big black smoke) – too much smoke means the fire is choked and the temp drops
  • Small pieces of wood often -> rhythm is important
  • Having cones 5/6/7 was good.
  • Need to experiment with better cone positions
  • In this firing:  Had difficulty getting temp up to cone 6 in the end as it was already dark and we tried to rush it (fire out the chimney might bring on the  fire brigade)

Closing up:

  • Have the bricks for closing up somewhere where they can be found
  • Don’t forget to take in the road sign 😉
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