Group C Lab Data: Week 8, Pottery Firing

Group C: Reed, Sam, Astrid, and Aubrey

This week, we were able to fire our now bone-dry pots from last week’s lab in bonfires outside. Our main focus was the similarities between firing practices of pottery and cremation, keeping in mind the relationship these two practices may have had in the minds of premodern peoples, such as the people of Early Medieval England. We also were able to experience and think about the social experience of pottery firing, which we enjoyed a lot.


  • Firewood and newspaper for kindling, matches
  • Blue and yellow laser thermometers
  • Digital scale
  • Phones for timing and measuring pots (the tape measure was in high demand)
  • 21 bone dry pots of stoneware and Arb clay
  • Damp bark for smothering

Pot measurements:


PotWeight (g)Diameter at lip (in)Height (in)
Aubrey’s Arb clay (Pot A)16232
Reed’s Arb clay (Pot B)1273.52.75
Reed’s stoneware (Pot C)23673
Sam’s stoneware (Pot D)2902 3.5

Note: all pots had temper in them

Also, the measuring tools we used were not sensitive enough to determine the pots’ wall thickness.

Post firing

PotWeight (g)% Weight lossDiameter at lip (in)Height (in)
Aubrey’s Arb clay (Pot A)1535.532
Reed’s Arb clay (Pot B)1205.53.52.75
Reed’s stoneware (Pot C)2081273
Sam’s stoneware (Pot D)N/AN/AN/AN/A



Time elapsed since pots were placed around the fire (mins)Notes, e.g. temperature of fire and pots (in Celsius), lost pots, weather, etc.
0Arb clay pots placed in a circle around the fire (about 1 ft away)
3Center of fire is 800°, periphery is around 650°–700°
5Stoneware pots added to the circle around the fire
11Move all pots inward by ~1 in
13Fire is 800°–870°
15Move all pots in by ~2 inPot temperatures taken:Pot A: 92°Pot B: 88°Pot C: 90°Pot D: 96°
17Move all pots in by ~1 in; it also starts to rain lightly
21The wall of one of Astrid’s pots explodes, likely because it was fairly thick
23Pot temperatures taken:Pot A: 130°Pot B: 145°Pot C: 120°Pot D: 114°
35Fire temperature ranges from 710°–930° on one side
37Move pots away from the fire to rake the coals
40Fire is 670°–700°Pot temperatures taken:Pot A: 165°Pot B: 130°Pot C: 87°Pot D: 95°
43Fire is 600°
44Stack pots on the coals
46Start rebuilding the fire in a teepee style
47Fire is ~250°–500° in various partsPot pile is ~80°–120°
53Fire is 450°Pot pile is 158°We keep hearing things pop, and it’s difficult to tell if it’s firewood or pots
55Pot pile is ~330°
66Fire is 750°–800°
79Move logs inward so their unburnt ends go into the fire
82Fire is up to 920° in the center, 600° on peripherySome pot temperatures taken (others not visible):Pot A: 750°Pot B: ~550°–800°
84Starts to rain a bit
89Rain gets heavy, evaporates off the pottery when it hits
90Begin to smother the fire with damp bark; the fire is mostly coals at this point
96Finish smothering; our fire is definitely the smokiest of the three fires
104Adding buckets of smaller bark pieces and dirt; dirt seems to be more effective than the bark at smothering the fire

Next morning

Time elapsed since start of lab Notes
21 hrs, 0 minThe bonfire is still burning
21 hrs, 1 minExcavation begins
21 hrs, 3 minFire is 600° at the middle, 400° at the edge
21 hrs, 6 minMost pots are 250°—450°
21 hrs, 27 minMost pots are ~140°–250°
21 hrs, 43 minFire is still 600°; most pots can be handled by hand


  • 18 of 21 pots survived as whole vessels, but lost chunks of their exterior 
  • 13 of 21 pots survived totally unscathed
  • None of the Arb clay pots broke—a surprise, since we thought the rocky inclusions in the clay body would make them more likely to explode during the firing
  • Unfortunately, one of our measured pots (Pot D) was destroyed during the firing
  • Most of the pots were blackened by the reducing atmosphere of the firing; some even had an iridescence reminiscent of an oil spill from the soot.
  • The pots did not appear to change in size, though admittedly our iPhone measuring app was not very precise, so subtle changes in dimensions would not be noticeable 
  • The pots got lighter:
    • Pot A lost 9 g
    • Pot B lost 7 g
    • Pot C lost 28 g
    • Pot D has no data
  • Although it’s difficult to confirm with only one stoneware pot being measured, it seems possible that stoneware may lose more water than Arb clay does, since the surviving stoneware pot lost approximately 12% of its original weight in the firing, while both Arb clay pots only lost 5.5% each.  
  • Excavating the bonfire had some similarities to the excavation of the cremation pyre from a few weeks ago. The blackened surface of the pottery resembled the charred bone of the pig shoulder, though none of the pots or sherds became bone-white in the way that superheated bone does. However, picking through the remains of the fire and trying to discern what was ceramic and what was surviving bark or rocks was very similar; it is easy to imagine that the people of Early Medieval England made the same connection between pottery firing and cremation. 

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