AS
Audrey Stamm
Potter / Sculptor
April 2021 Saggar Firing
Each of the smaller vessels here are from an earlier firing, but the process is the same. Wheel thrown, 3 coats of Terra Sig and burnished with plastic wrap after each coat.
Ferric Chloride applied to bisque ware. Salt, sugar, miracle grow is added to the final wet application and once dry, wrapped in 3 layers of heavy aluminum foil.
This was polished using Pledge Floor Gloss.
Each of the smaller vessels here are from an earlier firing, but the process is the same. Wheel thrown, 3 coats of Terra Sig and burnished with plastic wrap after each coat.
Process
Construction
This group of pots are a continuation of the saggar firings I have been doing since last summer. The Large Vessel (#200) was wheel thrown for the bottom 2/3rds. After that the vessel was hand build using large coils of clay until complete. The three other vessels ( #204, 205 and 201) were wheel thrown, trimmed and smoothed using a rubber rib.
Pre Firing Surface Treatment
The Large Vessel ( #200) was burnished at the leather hard stage using a rubber rib, then plastic wrap. The three other vessels (#204, 205 and 201) Had Terra Sigilatta applied at the leather hard stage( 3 coats) and hand burnished using plastic wrap between each coat. After burnishing, they are left to fully dry ready for bisque firing.
Bisque Firing
The Large vessel (#200) was standard bisque fired in David's gas kiln to cone 07. The other 3 vessels were bisque fired to cone 09, also in David's gas kiln at Eversfield Ceramics.
Saggar Preparation
Each saggar was constructed with 3 layers of heavy aluminum foil. The first layer of foil was crinkled to allow random air pockets to form. Prior to wrapping, the pieces were coated with 3 coats of Ferric Chloride. On the last wet coat, Salt, sugar and/or miracle grow was added to the surface in random patterns. One to two handfuls of sawdust was added to each of the saggars prior to wrapping up tightly. Saggars were then stacked into the kiln. The kiln shelf was 10 inches above the kiln floor.
Large Saggar Vessel #200
Saggar Firing Process
Here is the firing schedule for the April 7th saggar firing. Kiln was David's gas kiln at Eversfield Ceramics studio. NOTE: Ferric Chloride seems to be easily effected by both the final temperature and the length of firing time. The kiln stayed in oxidation state for the entire firing.
​
Cold start - temperature of the firing room was approx 0'c. ( Cool spring day here in the rockies)
Back burner only turned on to warm the loaded kiln. Flu bricks were steepled.
Moderate climb (1' every 4 - 5 seconds) to reach 235'c ( took 15 min) then held for 8 min
Turned on front burner and adjusted the flu bricks to 3 inches apart
Moderate climb to quartz inversion stage of 575'c (took 35 min) then held for 10 min
Turned up burners to increase firing rate to 1' every 2 - 3 seconds to 667'c ( took 24 min) then held for 15 min
Aluminum foil starts to break down around 650'c, but we turned up burners to final temperature of 700'c then shut off, as the foil seemed to still be intact.
Allowed kiln to cool naturally.
Materials Used
Clay
Large vessel #200 was made of Cone 10 - 570 Plainsman white stoneware. The three smaller vessels, (# 204, 205 and 201) were constructed using Cone 6 Laguna Bmix white stoneware.
Firing Materials
Ferric Chloride - 3 coats applies to dry bisque ware.
Table Salt
Sugar
Miracle grow ( copper sulphate is suspected to be the active ingredient causing flashing)
Coarse steel wool
Dry sawdust
​
Pot #204 - Sugar, steel wool and sawdust
Pot #205 - Salt, sugar and sawdust
Pot #201 - Salt, miracle grow and sawdust
Large Vessel # 200 - Salt, sugar, miracle grow and sawdust
Results
This firing produced more variety in the final colours, especially for the large vessel. Hotter areas seem to be deeper colours.
The use of the coarse steel wool produced very dark areas. Would reduce the amount of steel wool to produce more feather like results. The miracle grow seemed to pit the surface, I would use less of it in future, or find a way to bring it close to the surface, but not actually stuck to the wet Ferric Chloride.
Comments / Learnings
The Large vessel was over-fired during the bisque firing process and therefore lost some of the shine from burnishing.
It will be worth experimenting with the coarse steel wool to produce some effects that can be controlled. Will also try to put the sawdust on the inside of the vessels so that the black bottoms are not present. I am noting that the temperatures on the pyrometer might not have reflected the actual temperatures inside each saggar. Especially the larger vessel. The biggest gauge was the lack of breakdown of the aluminum saggar in David's kiln. In previous firings, my smaller raku kiln seemed to disintegrate the aluminum completely in places with only a temperature reading of 660'c.