The Effect of Firing Time on Glaze
Chemistry(Deciphering Ancient Practice Through Forensic Analysis)
William M. Carty Kazuo Inamori School of Engineering
Alfred University
NCECA · 2012
Seattle, Washington
William M. Carty
Hyojin Lee Alfred University
Background
Glaze-body interaction is extensive during firing.
This results in a significant shift in the glaze
chemistry that increases with firing time.
Modern bodies average 60 µm penetration depth
(the thickness of a typical human hair).
The analysis of a 12th Century Korean Celadon,
from the Koryǒ period (918-1392 CE), indicated
approximately 200 µm penetration depth!
This was significantly greater than anything we
had evaluated up to that point.
Examples: Time-Temperature Results12th Century Bowl
Koryǒ period
(918-1392 CE)
Gangjin, Korea Gimjae, Korea
4 days at 1180°C
3 days at 1210°C
4 days at 1050°C
Analysis of Ancient Shards
This analysis can be tricky:
Shards from kiln sites may not have been
properly fired (discarded as inferior).
How to identify the original body-glaze interface How to identify the original body-glaze interface
(when the glaze was applied)?
The sample will likely be destroyed.
Analytical Tool: WDS
Wavelength Dispersive Spectroscopy (WDS), an electron
microscopy tool, allows us to map chemistry.
By comparing chemistry maps, we can identify chemistry locations and
ultimately chemistry shifts.
There is (essentially) no Ca in the
Gla
zeThere is (essentially) no Ca in the
body, therefore all Ca comes
from the glaze.
Need the original body-glaze
interface (as applied).
Ca MapBo
dy
Gla
ze
Ca Map
Example from a modern body
Alumina in the body served as a marker.David Finkelnburg, M.S., Alfred University, 2006
Zircon used as a marker in
experimental studies
Map of Zr Map of Ca
Original Body-Glaze
Glaze
1300°C · 1 hour
Original Body-Glaze
Interface
Body
Zircon is typically not soluble in either the body or glaze.
It was added to the body to provide a marker.
Glaze penetration occurs around the zircon particles.
Results of experimental studies
1300°C
1 hour
10 hours
1 week
Thomas Rein, B.S., Alfred University, 2010
Gimjae Shard Sample
Penetration Depth:
∼100 µm
Gangjin Shard Sample
Penetration Depth:
∼170 µm
12th Century
Koryó Period Bowl
Mullite (from grog) now serves as the marker.How to identify the original body-glaze interface?
Penetration Depth: ∼200 µm
Greater penetration of the glaze into the
body means a greater shift in chemistry
Glaze
chipped from
the body is far
from the from the
original glaze
chemistry
This example
assumes that the
penetration depth is
equal to the
application thickness
Chemistries of Korean Celadon
Bodies and Glazes
SiO2 Al2O3 TiO2 Fe2O3 Na2O K2O MgO CaO
Glazes
57.6 12.4 0.1 2.1 0.7 2.8 4.2 17.7
58.1 13.9 0.2 1.4 0.5 2.9 1.8 19.9
59.6 14.1 0.1 1.4 0.8 3.8 2.7 16.0
BodiesWe
igh
t %
Bodies
76.0 17.0 0.8 2.1 0.7 2.5 0.5 0.3
73.0 17.5 0.9 2.8 0.8 2.6 0.7 0.2
73.0 18.0 1.2 2.5 0.9 3.4 0.5 0.5
Nigel Wood, Chinese Glazes, 1999
Glaze
2.24 0.31 0.00 0.05 0.02 0.08 0.16 0.73
Body
19.8 2.7 0.19 0.49 0.21 0.48 0.23 0.09
UM
FW
eig
ht
%
Comparison with modern ceramics?
Modern bodies: 60 µm penetration depth.
Ancient bodies: 200 µm penetration depth.
How to rectify?
Ancient bodies must have been held at
temperature for significantly longer times. temperature for significantly longer times.
Body analysis indicates much lower firing
temperatures.
We need a new matrices.One for firing temperature &
one for glaze penetration depth
Sili
ca
UM
F in
Gla
ss P
ha
se
14
16
1300°C
Body glass chemistry at different temperatures
Korean Celadon body
Firing Time (hours)
100 101 102
Sili
ca
UM
F in
Gla
ss P
ha
se
8
10
12
1200°C
1250°C
1300°C
Furnace Setting
1200°C
1250°C
Penetration depth at different temperaturesG
laze P
enetr
ation D
epth
(µm
)
103
1200°C
1250°C
1300°C
Korean Celadon body and glaze – estimated chemistries
Firing Time (hours)
100 101 102
Gla
ze P
enetr
ation D
epth
(
101
102
Firing conditions for Korean Celadons?
SampleSilica
UMF
Glaze
Depth
(µm)
Firing time
(hours)
Firing
Temperature (°C)
12th Century
Koryó bowl11.8 190 100 1180
Koryó bowl
Gangjin Shard 11.1 170 70 1210
Gimjae Shard 7.5 100 100 1050*
* Data and sample condition (poor strength, continuous
porosity) indicates this shard was underfired.
Correcting glaze chemistry to reflect
glaze-body interaction
Used a “rule of mixture” (ROM) approach.
dG,f × ChemG,f = dB × ChemB + dG,A × ChemG,A
d ≡ final glaze thickness.dG,f ≡ final glaze thickness.
dB ≡ depth of body penetration.
dG,A ≡ Original glaze application thickness.
ChemG,f ≡ Fired glaze chemistry.
ChemB ≡ Chemistry of the body.
ChemG,A ≡ Chemistry of glaze as applied.
Original Glaze Chemistry (as applied)
SiO2 Al2O3 Fe2O3 Na2O K2O MgO CaO
35.6% 7.5% 0.4% 0.5% 3.8% 6.8% 46.7%
Seger
0.564 0.070 0.002 0.007 0.039 0.160 0.794
Final Glaze chemistry if Final Glaze chemistry if
the glaze batch is
calculated to match the
fired glaze chemistry
(ignoring the body
incorporation).
Glaze chemistry for modern firing
Calculated glaze
SiO2 Al2O3 Fe2O3 Na2O K2O MgO CaO
52.3% 11.8% 1.3% 0.6% 3.4% 4.1% 26.7%
Seger
1.393 0.186 0.013 0.016 0.058 0.163 0.764
Calculated glaze
batch chemistry for a
modern glaze to
match ancient glaze
(corrected for modern
firing cycles and
incorporating body
interaction).
Proposed batch for ancient celadon
and modern equivalent (1250°C)
G-200 EPK Whiting Flint
Koryǒ Celadon
(100 hour soak)19.9 4.1 67.5 8.5
(100 hour soak)
Modern
(3 hour soak)21.9 14.5 44.9 18.7
Similar feldspar, but a significant increase in clay and silica (due to
the reduction in glaze-body interactions as
a consequence of much shorter firing times).
Also, much less whiting.
Conclusions
Glaze-body interactions significantly alter the glaze
chemistry during firing.
Compensating for body-glaze interactions leads to a
very different glaze batch compared to
the batch calculated from a glaze chip.
very different glaze batch compared to
the batch calculated from a glaze chip.
Knowing the extent of the glaze-body interactions is
essential to formulate glazes
for modern firing schedules that mimic
ancient results.
Acknowledgements
Korean Institute of Ceramic Engineering and Technology (KICET), Korea
David Finkelnburg (M.S., 2006)David Finkelnburg (M.S., 2006)
Tom Rein (B.S. Thesis, 2010)
Chorwon Kim
Matt Katz
Hyojin Lee (my co-author)
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