'Tall Shaft' Iron Smelt
Build : May 2003
Smelt : June 2003

This table created by Neil Peterson, working from field notes taken by Gus Gissing

Actual Time Elapsed Time Notes
1424h   The first charge was added along with a 1.5 Kg of charcoal.
1435h T+0:11 The charcoal leftovers from the ore roasting -- along with no doubt some ore was added.
1436h T+0:12 The second charge with 1.5 Kg of charcoal was added
1439h T+0:15 0.75 Kg of charcoal was added.
1448h T+0:24 3 Kg of chorcoal was added.
1452h T+0:28 The third charge was added after another 3 Kg of charcoal.
1457h T+0:33 We altered the angle of air pipe by raising the back end 1 cm. Some more cobb was added to adjust the seal of the pipe.
1501h T+0:37 3 Kg of charcoal added.
1506h T+0:42 We noticed a small amount of slag appearing by the fire bricks.
1508h T+0:44 The fourth charge was added along with 3 Kg of charcoal.
1512h T+0:48 The tuyure was cleared of slag by rodding it out.
1517h T+0:53 The tuyure was cleared of slag by rodding it out.
1520h T+0:56 Another 1.5 Kg of charcoal.
1523h T+0:59 The fifth charge and another 3 Kg of charcoal was added.
1528h T+1:04 The tuyure was rodded out.
1535h T+1:11 3 Kg of charcoal was added.
1538h T+1:14 The tuyure was rodded out.
1539h T+1:15 The tuyure was rodded out.
1540h T+1:16 1.5 Kg of charcoal was added.
1545h T+1:21 The tuyure was rodded out.
1550h T+1:26 The air was run up to 1/2
1552h T+1:28 Air down to zero and the doors were opened to let the slag out. We were overjoyed to see liquid pour out (ok perhaps pour is an overstatement as the first slag tapping was rather viscous). In hindsight it was our guess that this was the still liquid parts of the bowl itself flowing, rather than the liquid slag that forms above of the bowl. Some was set aside as samples the rest was (as planned) added back into the top of the smelter. The doors were closed, air returned to 1/8th, and another long burn occurred.
1556h T+1:32 The tuyure was cleared again.
1601h T+1:37 The wedge was removed from the tuyure to raise the air over the slag better and the air was bumped up to 5/16ths.
1606h T+1:42 1.5 Kg of charcoal was added.
1610h T+1:46 Air was adjusted to 1/2 flow.
1614h T+1:50 Air was adjusted to full.
1617h T+1:53 1.5 Kg of charcoal was added.
1620h T+1:56 Air was adjusted to 1/2.
1623h T+1:59 1.5 Kg of charcoal was added.
1624h T+2:00 The air was set to zero, the doors were opened and out came the slag (much runnier this time). This time we think we actually tapped into the slag we wanted. As of this point things were going exactly as expected. The slag was sampled and the remainder added back in to the top.
1632h T+2:08 The air was turned back up to 1/2.
1636h T+2:12 3 Kg of charcoal was added.
1637h T+2:13 The doors were closed.
1641h T+2:17 The tuyure was rodded out.
1644h T+2:20 The tuyure was rodded out.
    Now we come to the painful part. Something went wrong. We aren't sure why but the slag pool built up enough to partially block the airway. This deflected the air upwards allowing a cool spot to form immediately below the airway. This caused more blockage of the airway. In addition the deflected airflow produced a hot spot above the airway. In this picture you can see the beginning of the burn through.

We reacted to attempt to block the burn through but it was in vain. All that came of this was a heat sink that reduced the smelter temperature to a point that would not finish the smelt.
1650h T+2:26 More charcoal was added.
1701h T+2:37 Another 3 Kg of charcoal was added.
1705h T+2:41 The air was raised to 1/2.
1708h T+2:44 2.25 Kg of charcoal was added.
1713h T+2:49 The next tap was done with a good slag flow.
1716h T+2:52 Closed the tap hole and added 1.5 Kg of charcoal. There had been a little slag from the first tap sitting without coming out. In this tap it came out. This let us have a comparison of the first and third taps side by side. The third tap was noticably less dense.
1725h T+3:01 The turrie was cleaned again.
1727h T+3:03 1.5 Kg of charcoal added. At this point we became concerned that the volume of slag was so large that it might not be possible for the reducing charge to work. We decided to tap off some of the slag to make room.
1737h T+3:13 We added more charcoal and began the tap. Unfortunately this tap really didn't produce any slag.
1741h T+3:17 We added the sixth (reducing) charge. The tuyure was cleared again then charcoal added to top up the furnace. Three more turrie clearings were done in the next 9 minutes.
1756h T+3:32 Another 1.5 Kg of charcoal was added.
1759h T+3:35 The air was cranked up to full as air did not seem to be moving through the turrie due to the damage to the wall.
1800h T+3:36 We tried another slag tapping to lower the level and try and get air through the turrie. This time we did not put the top brick back in.
1806h T+3:42 Another 1.5Kg of charcoal was added.
1814h T+3:50 The bottom brick was removed and a tap done. This did reduce the level clearing the turrie and letting the furnace begin to roar again.
1816h T+3:52 Another 1.5Kg of charcoal was added.
1826h T+4:02 We fired up a propane forge to take the bloom and keep it hot -- as you will see though we never did find the bloom.
1830h T+4:06 We went to do the final pull of the slag. None came pouring out and we had to reach far up into the smelter attempting to pull any out. It was, however, too cold. We opened a larger door in the smelter to pull out the slag and bloom. (Next time we need to have two doors -- a small one for the slag and a large one for the bloom). Although we got a large cascade of very hot charcoal that wasn't quite what we were after. The smelter was knocked over. It broke apart and some materials were removed. Samples of these have been sent out for testing. All appear rather glasslike but their weights are shockingly different. Clearly some are "pure" slag while others have a high metal content.