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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 NameArchaeologyDescriptionNotes
GoderichRibe OvalDual 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.
KarenRibe OvalDual 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.
NeilRibe Circular designA "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. 
SarahRibe OvalA 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. 
WendiRibe OvalStandard 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 furnaceThis 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/furnaceGoderich-#1Karen - #2Neil - #3Sarah - #4
chimney 577.61005650
7581070* 
815652
700971
682.0* 
452
451
crucible 390260307
451222220
port at door 1000962854.3
8748601200 (film)
860 900
Airspeed (m/s) 7.3318.064.3913.53
Airflow (Lpm) 0.020.050.010.04
Time to Heat6:10 1:451:00
Time at Temp18:10 10:2011:30

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:
Rob and Jean making beads on the "Neil" furnace from tesserae.
Darrell making a bead on the 'Karen' furnace.
Sarah making a bead on the 'Sarah' furnace.


Notes
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The "Karen" furnace Airsource for "Neil" furnace The "Neil" furnace The "Sarah" furnace
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Layout of "Karen" furnace Loading port of "Karen" furnace Darrell working a bead Bead in the furnace
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Bead in the chimney A busy day Beads and temperatures Watching a stringer
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Heating a tesserae Drawing a stringer Finished stringer Tweezer Marks
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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









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Bead 9-11A Bead 9-11B Bead 9-11C Bead 9-11D
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Bead 9-11E Bead 9-11F Bead 9-11G Bead 9-11H
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Bead 9-11I Bead 9-11J
Text © Neil Peterson, 2011
Photographs © Individual artists
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