Bead Furnace Burn Jul 18 2009

---

Creator: Neil
Materials: Cobb (Manure, clay), charcoal, glass
Location: Treheima
Notes: Used blower, small number of experienced beadmakers, lots of video and temperatures

---

This was the second use of the oval mark V. The base is a 30x60cm oval matching one of the bases found at Ribe. This style can be set with two working ports - one on each short side. The port for the bellows is in the center of the long side. Opposite that port is a chute for loading charcoal currently blocked with a crucible for annealing. At the top are two chimneys with another pot for annealing between them. The chimneys were built a bit smaller than the mark III and the annealing pot a fair bit deeper.

We filled the annealing pot with sieved ash and got some good annealing temperatures in that location. The crucible was rather too warm for annealing this time.

This melt was targetted at a smaller group of experienced bead makers. This allowed us to spend more time making beads, learning more about working with the tesserae, and eliminating one variable (skill) from the annealing problem. We also got some good pictures and video of the activities.

Scaled Drawing	Fire zones	Turning Reticella	Heating tesserae
Winding on tesserae	Working in the chimney	Marvering for shape	Marvering
Pulling stringers	Working multiple beads	Putting beads in the annealing pot	Adding decoration
Taflmaðr	Darrell's better beads (and taflmaðr)	Rob's better beads	Jean's better beads

Maintaining a useful temperature is HARD in these furnaces. A charcoal load gives time to make a single bead at each side. Tiny changes in the direction of air inflow can make big changes to the heat locations inside the furnace. This time we would up in a decent pattern

• Load with charcoal
• wait a minute or two for the heat to come back up
• work
• when the temperature drops, push the remaining hot charcoal into the "hot zone" where it has burned away
• temperature rises very fast again allowing a little more work
• repeat from the top

A type K thermocouple was employed to roughly measure exhaust gas temperatures at one of the top ports over the experiment. A roughly 6 mm (1/4 inch) diameter hole was drilled into the wall of the furnace, just down from the lip of of the port. The probe was extended into the opening about 1 cm. Although the probe was placed early in the experiment, and readings were constantly monitored, unfortunately the recorded data currently extends over a relatively short time sequence. Since the thermometer was included in the frame of the overview video shot we will be able to extend this table when we have time to analyze the video in depth.

TIME	TEMP	EVENT
1:03	900
1:04	1000
1:07	900
1:09	700
1:10	800
1:11		charcoal fill
		change method
1:15	755
1:16	655
		adjust charcoal
1:17	925
1:18	810
1:19	850
1:20	890
		adjust charcoal
1:21	910
1:22	830
1:23	860
1:24	870
1:25	840
1:26	850
1:27	820

We confirmed that Darrell's tesserae method worked repeatably. It is unlikely to be the only usable method but it can work and we have some good video of it

• work is done inside the furnace through a side port
• glass tiles placed on flat surfaced piece of charcoal (which can be used two or three times)
• wait till glass tile heats till edges just start to slump
• make sure your mandrel is well heated (to orange)
• touch mandrel to one corner of the tile to affix small corner of glass
• raise and twirl mandrel. This effectively pulls a stringer shaped finger of glass off the tile
• now the process is like working with a rod, thickness of the stringer is controlled mainly by height the mandrel is lifted above the tile
• This appears to reduce the amount of ash contamination, plus produce a correctly shaped bead (rather than the irregular shape produced by grabbing the entire tile at once)

A video of working with tesserae can be seen on youtube