Bead Making & Temperature Measurements
10 Sep, 2011
The goal of this day was to get some temperature measurements for different
designs of furnaces for a paper we are working on.
Before we begin the discussion it is worth discussing experimental variables. This experimental series
is still near the start, which means we have a number of variables still unanswered. We are mostly using
matched COE glass for the beads to eliminate one source of breakage. Some beads, however, are being
built of mosaic tesserae to understand the working properties of tesserae. Although in some experiments
we work with a bellows to supply air, for this day we used hair dryers to provide a matched amount of air,
even if it turns out they don't provide identical amounts of air.
As the series progresses we will be working to solve those (and many other) variables.
Four different furnaces were available, but due to available staff only
3 were running on this day. The terms left and right are used as you
would view the furnace when facing the airway.
| Furnace Name | Archaeology | Description | Notes |
|---|
| Goderich | Ribe Oval | Dual chimney oval furnace,
cobb construction. Internal construction includes gentle slopes from
walls to floor, and a large air diverter opposite the air port. There
is no opening cut for charging - charcoal is added through the
chimneys. Working ports are cut into each end. Right port uses cuts
angled up into the furnace. Left port cuts angle down into the furnace.
Right port produces more heat onto the bead maker. | Good functional furnace with 10 hours of burn time. Not used on this day. |
| Karen | Ribe Oval | Dual chimney oval base cobb furnace with
a much thicker wall design (5 cm) and is longer in length versus width
than normal. It is also fairly tall. The internal air diverter is
moderately sized. The annealing pot is long and narrow but not very
deep and sits between the chimneys. Working ports were cut in each end
with cuts sloping up into the furnace. A charcoal loading port was cut
into the back wall opposite the air inlet and above the diverter. | This furnace seems to spark less, perhaps due to the larger internal volume. Total burn time 5 hours. |
| Neil | Ribe Circular design | A "teapot" design.
Single chimney round base cobb furnace, with annealing pot attached to one side. A single
working port cut into the body. Charcoal is loaded through the working
port or chimney. Walls are standard thickness (3cm) and have a very
pronounced curve joining walls and floor in a bowl shape to aid in
charcoal concentration. The working port is cut high on the wall. | |
| Sarah | Ribe Oval | A smaller version of the
standard shape built with a single chimney. This had originally been
intended to work as a single working port but the plan was changed. A
port was cut into each end, and a diverter added to the inside. The air
port was cut in the usual location. | |
| Wendi | Ribe Oval | Standard size and shape, high
and wide filling 1'x2' kiln plate. 2 large chimneys, 2 working ports,
substantial diverter, tuyere mid-way up wall coob furnace | This furnace was burned for two weekends but did not survive transport between locations. |
Several videos were made to allow us to plot temperature over time. These are the results.
Operating temperatures
All temperatures are in celcius.
A number of temperature measurements were taken at various points in
the burn cycles. These are summarized in the following table:
Temperatures - * = sweet spot, + = end of cycle
| local/furnace | Goderich-#1 | Karen - #2 | Neil - #3 | Sarah - #4 |
|---|
| chimney | | 577.6 | 1005 | 650 |
| 758 | 1070* | |
| 815 | 652 |
| 700 | 971 |
| 682.0* | |
| 452 |
| 451 |
| crucible | | 390 | 260 | 307 |
| 451 | 222 | 220 |
| port at door | | 1000 | 962 | 854.3 |
| 874 | 860 | 1200 (film) |
| 860 | | 900 |
| Airspeed (m/s) | 7.33 | 18.06 | 4.39 | 13.53 |
| Airflow (Lpm) | 0.02 | 0.05 | 0.01 | 0.04 |
| Time to Heat | 6:10 | | 1:45 | 1:00 |
| Time at Temp | 18:10 | | 10:20 | 11:30 |
At one point a temperature was taken while a bead was being worked in
the chimney of the 'Karen' furnace. Below the bead the temperature was
900 Celcuis while above the bead it was only 850. This difference in
temperature, with the heat coming from below provides a very different
working environment when compared to the torch heat people are more
used to working with.
In addition two videos were recorded showing the thermometer with the
thermocouple fixed in the chimney. These videos were examined to
produce the following time/temperature graphs.
Compressed video (8x normal speed) to go with the chart below
Compressed video (8x normal speed) to go with the chart below
We also got a chance to run and record the "goderich" furnace the next weekend.
Compressed video (8x normal speed) to go with the chart below
Videos
We also have a few videos available of beads being made in the furnaces:
Notes
- We need to cut ports and tuyere with a 2-3 weeks of making the furnace - dry clay is too hard to cut well.
- Use thick walls to cut down on heat loss
 |
 |
 |
 |
| The "Karen" furnace |
Airsource for "Neil" furnace |
The "Neil" furnace |
The "Sarah" furnace |
 |
 |
 |
 |
| Layout of "Karen" furnace |
Loading port of "Karen" furnace |
Darrell working a bead |
Bead in the furnace |
 |
 |
 |
 |
| Bead in the chimney |
A busy day |
Beads and temperatures |
Watching a stringer |
 |
 |
 |
 |
| Heating a tesserae |
Drawing a stringer |
Finished stringer |
Tweezer Marks |
 |
 |
| |
| Waiting for a calm |
Bead in the chimney |
Beads Produced
Darrell managed to record the beads that he produced in the following
table. The "Callmer" typology information has been included with them
in order to aid in comparing them to other beads.
| BEAD |
BASE COLOUR |
PATTERN COLOUR |
PATTERN TYPE |
SURFACE |
IMAGE |
GLASS |
SHAPE
see below |
DIAMETER mm |
WIDTH mm |
MANDRIL |
HOLE MAX mm |
HOLE MIN mm |
WORK LOCATION |
WORK DETAIL |
BREAK? |
PIECES |
SHAPING |
| 9-11A |
red |
blue |
stringer |
|
9-11A.jpg |
cane |
flat oval |
10.4 E |
5.6 E |
ss rod |
3.7 E |
|
chimney |
|
removal |
2/3 only |
|
|
209-183
|
|
311, 503
|
|
|
|
124-152
|
164
|
|
|
|
|
|
|
|
|
|
| |
| 9-11B |
red |
black |
stringer |
|
9-11B.jpg |
cane |
flat oval |
9.6 |
4.6 |
ss rod |
3.6 |
|
chimney |
|
chip in annealer |
|
|
|
209-183
|
|
311, 541
|
|
|
|
124-151
|
164
|
|
|
|
|
|
|
|
|
|
| |
| 9-11C |
red |
black |
line |
|
9-11C.jpg |
cane |
oval |
12.6 E |
9.1 |
|
4.6 |
|
chimney |
|
removal |
1/2 only |
draw to one end |
|
209-183 OR 205-183
|
|
311, 503 OR 313,501
|
|
|
|
124-152
|
165 |
Note the two descriptions of decoration -
is this a red bead with 3 black lines, or a black bead with a red line
that has a black line on it?
While the maker may know how he did it - would the archaeologist be able to tell the difference? |
| |
| 9-11D |
orange |
|
|
|
9-11D.jpg |
tesseri |
flat oval |
11.5 |
5.5 |
iron |
5.3 |
4.7 |
port A |
|
|
|
|
|
208-183
|
|
|
|
|
|
124-151
|
165
|
No orange beads of this type found, but it
is found in other colours: white, black, yellow, red, dark brown, dark
blue, turquoise |
| |
| 9-11E |
yellow |
blue-grey |
line |
|
9-11E.jpg |
tesseri |
oval |
10.3 |
7.2 |
iron |
3.6 |
2.9 |
port A |
|
|
|
points both sides |
|
206-183
|
|
311, 503
|
|
|
|
124-152
|
164
|
|
|
|
|
|
|
|
|
|
| |
| 9-11F |
yellow |
|
|
rolled |
9-11F.jpg |
tesseri |
barrel |
12.4 |
12.5 |
iron |
4.1 |
3.5 |
port A |
off floor |
next day |
thirds |
ash coated |
|
206-183
|
|
|
|
|
|
124-153
|
165
|
No known matches |
| |
| 9-11G |
blue |
brown |
blob |
cut bars |
9-11G.jpg |
tesseri |
barrel |
13.7 |
11.8 |
iron |
4 |
2.6 |
port A |
|
|
|
|
|
214-183
|
|
??
|
|
|
|
125-152
|
165
|
No real matches for that "blob" decoration |
| |
| 9-11H |
blue |
red |
stringer |
|
9-11H.jpg |
tesseri |
oval |
9.5 |
5.3 |
iron |
3.1 |
2.8 |
port A |
off spoon |
removal |
half |
|
|
214-183
|
|
311,503
|
|
|
|
124-152
|
164
|
|
|
|
|
|
|
|
|
|
| |
| 9-11I |
light blue |
black |
dots |
|
9-11I.jpg |
cane |
oval |
13.6 |
8.9 |
iron |
4 |
3.5 |
chimney |
off bottom surface |
in annealer |
half |
slightly irregular |
|
215-183
|
|
301,321
|
|
|
|
124-152
|
165
|
|
|
|
|
|
|
|
|
|
| |
| 9-11J |
blue |
black |
stringer |
|
9-11J.jpg |
tesseri |
round |
10.6 |
9 |
iron |
3.3 |
2.3 |
port & chimney |
stringer off spoon |
removal |
1/2 only |
|
|
215-183 |
|
311,503 |
|
|
|
124-152 |
164 |
|
|
|
|
|
|
|
|
|
 |
 |
 |
 |
| Bead 9-11A |
Bead 9-11B |
Bead 9-11C |
Bead 9-11D |
 |
 |
 |
 |
| Bead 9-11E |
Bead 9-11F |
Bead 9-11G |
Bead 9-11H |
 |
 |
| |
| Bead 9-11I |
Bead 9-11J |
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