My
research of black and brown glazes was inspired by a catalog titled Hare’s Fur, Tortoise Shell, and Partridge
Feathers that accompanied an exhibition of Song Dynasty dark glazes at the
Harvard University Art Museum in 1996.
The author and curator, Robert D. Mowry, assembled the largest
exhibition of ancient Chinese dark-glazed pots to date from collectors and
museums around the world. On page 68 of
the catalog, he gives the ultimate percentage analyses (UPAs) of four dark
glazes. (For further clarification,
please see the explanation of UPAs below.)
These are the only UPAs of dark Song Dynasty glazes I have seen. Because of my ongoing interest in glazes, I
was very excited to try and replicate these glazes using only native Oregon
materials.
In
April of 2002, I researched Oregon geology in various libraries. I found a considerable amount of
information. Of particular value to me
was a rare Oregon State publication called Bulletin
64, a 1967 survey of a number of significant deposits of materials that
have commercial value. Some of these
deposits have been mined for a long time, some were never mined, but all of
materials and locations of these deposits were well-documented. This information, combined with Metzer’s
county maps, enabled me to find the approximate deposit locations, so that,
when on site, I could talk with local farmers and townspeople to find the exact
location of each deposit. I knew I was
looking for dark, high-iron materials, which in nature would appear brown to
reddish to black. The materials in Bulletin 64 that seemed most interesting
were deposits of pumice, cinders, syenites, granites, metallic oxides, and
clays.
I
planned three trips. The first trip was
to explore north and northeast Oregon.
The second trip would take me to southwest Oregon. The third trip would include a section of
the Oregon coast.
·
I remembered
a low-fire clay in Othello, Washington, about thirty miles northwest of the
Tri-Cities, that I had used forty years ago.
I thought this clay may be a good material for this project. I went up the Columbia River Gorge to see if
I could relocate this material. On the
way, I stopped frequently to investigate interesting outcroppings. East of the town of The Dalles, I found a
really dark, soft clay. I took a sample
of about twenty-five pounds, the usual amount for testing. Next I went up to the Tri-Cities and on to
Othello, which of course had changed a lot in forty years. But I was able to locate the material I was
looking for in what is now the city dump.
I gathered about two hundred pounds of the material, because I was
reasonably certain this material would work for my purposes.
·
I went on
to Pendleton, where I found a large deposit of pumice adjacent to Blue Mountain
Community College. I gathered a sample.
·
I went
south to Ukiah and revisited the clay and pumice outcroppings I had used seven
years ago in my celadon research. I
gathered about two hundred pounds of each material.
·
I
proceeded further south to Hamilton, to a location one-and-a-half miles
southeast of the town, where there are considerable amounts of manganese
dioxide nodules one can just collect off the ground. I gathered about twenty pounds.
·
I went
west to a large pumice deposit at Tumalo, about fifteen miles east of Sisters,
where I collected another sample.
·
I
proceeded further west to Santiam Pass, where near the top was a large cinder
cone. I gathered another sample
there.
·
I traveled
southwest to the Mount Ashland region to Williams, where approximately three
miles west of town, I gathered about two hundred pounds of limestone at the Bristol
quarry.
·
Next, I
drove south to Mount Ashland. Over the
years of glaze testing, the lightest-firing rocks I have found have invariably
come from Mount Ashland. But I had also
seen a few darker rocks on the mountain, although I had never tested them. At the base of the mountain, just west of
the town of Ashland, I found an old quarry that had been used to provide gravel
for Lithia Park many years ago. The
granite-type rock I found there was
dark and soft. I took a sample.
·
I went up
Mount Ashland looking for other dark rock.
It was not until I got to the very top that I saw a dark outcropping
that looked surprisingly similar to the rock I had found at the base. I took a sample to compare the fired results
of both.
·
The third
trip took me to the Oregon coast. At
Florence, I collected some beach sand.
·
I went
twenty miles north to Blodgett Peak, where there is a dark, syenite rock which
is quarried for bedrock. I collected a
sample there as well.
I
had, over the last month, processed many of the materials as I collected
them. I used my jaw crusher, roller
mill, and ball mills (each material is ball-milled for 18-24 hours to reduce the samples to fine powder of about 350
mesh) for making tests and samples for analysis. In all, I had collected:
·
dark clays
from Othello and The Dalles
·
light clay
from Ukiah
·
pumices
from Pendleton, Tumalo, and Ukiah
·
two
similar granite-type rocks from Mount Ashland
·
nepheline
syenite from the Blodgett Peak quarry
·
limestone
from the Bristol quarry
·
light sand
from the Florence beach
·
manganese
dioxide from Hamilton
In
addition, I collected wood ash from the fireplace of a friend who only burns
oak. And finally, I added another dark
clay I found behind my studio. The
collection of the above seemed like a good starting point for my research.
I
finished processing the last of the materials.
I mixed the finely powdered materials with water and applied each
material to white clay tiles for the first firing. I decided to fire all of the tests to cone 9 (1260C/2300F) in a
reduction (carbon-rich) atmosphere in my gas test kiln. Each fire takes approximately twelve hours
to reach temperature and another twelve hours to cool.
The
first tests were fired primarily to see the colors and degrees of melt. After the fire, I found:
·
the dark
clays and the cinders were very dark brown and immature (not melted)
·
the
manganese dioxide had changed only in color (to almost black), and otherwise
remained so immature it stayed powdery
·
the
pumices, the nepheline syenite, and the granites fired lighter and fairly
glass-like, indicating a more thorough melt
·
the two
granites were so similar I deducted they had to be from the same outcropping,
with one deposit at sea level, the other deposit at 3000’. Mount Ashland is an intrusive mountain, so
it is quite possible both deposits originally were part of the same outcropping
that has now been separated into two (or more) deposits at different locations
on the mountain
From
this initial test fire, I selected the most promising raw materials to be
analyzed:
·
Pendleton
pumice
·
Blodgett
syenite
·
granite
from the base of Mount Ashland I had labeled G-1 (granite-1)
·
The Dalles
clay
·
Othello
clay
·
cinders
The
limestone, oak ash, Ukiah clay, and Ukiah pumice had already been analyzed
during my earlier celadon research. The
manganese dioxide and beach sand have commonly known analyses.
The
six raw materials to be analyzed were weighed in 100-gram amounts and placed in
small plastic bags. I took them to the
University of Oregon Geology Lab for analysis using their x-ray fluorescent
spectrometer. I had to wait between two
and four weeks for the results, which would provide me with the ultimate
percentage analyses (or UPAs) of each material.
The
percentage weight analysis provides the exact percentage weight (i.e. the
percentage given in weights) of each oxide in a particular mineral. The main categories I needed to know were
the percentage weights of silicon dioxide, alumina oxide, sodium oxide,
potassium oxide, calcium oxide, magnesium oxide, iron oxide, and manganese
dioxide. I needed these analyses
because the published UPAs give the exact percentage weights of the oxides in
the
Song Dynasty black and brown glazes. So
with the analyses of my materials, I could then
calculate
these materials into the UPAs of the Song glazes. During this time, I processed ten pounds of each material to 350
mesh. This would give me a large enough
quantity to begin glaze testing.
With
the analyses done, and using the four published glaze UPAs, I was able to do
the calculations using several different materials. I calculated ten formulas with pumice as the main ingredient, ten
formulas with Blodgett rock as the main ingredient, and ten formulas with G-1
as the main ingredient. To see what
role the iron oxide played, I added the darker materials in varying amounts in
an effort to approximate the iron oxide contents of the published UPAs of the
Song glazes.
CHART 1: UPAS FOR NATIVE
MATERIALS USED IN GLAZES
The Dalles clay 51.75 8.4 0.5 1.4 0.63 - 37.4 - -
Othello clay 59.6 23.4 0.7 4.5 0.91 3.7 7.2 - -
Pendleton
pumice 71.6 14.6 2.6 4.8 2.3 0.86 3.2 - -
Manganese
nodules - - - - - - - 100.0 -
Cinders 51.3 20.1 1.5
3.0 11.1 3.4 9.6 - -
Bristol
limestone - - - - 55.5 - - - -
G-1 rock 63.0 17.4 3.5 4.1 4.43 2.8 4.7 - -
Florence beach
sand 100.0 - - - - - - - -
Blodgett rock 59.8 19.5 4.5 8.2 1.2 0.92 5.6 - -
Oak ash 14.4 3.2 1.6 4.0 56.1 2.4 1.0 - 17.3
CHART 2: PUBLISHED UPAS
OF SONG DYNASTY GLAZES
Black glaze #1
(temoku) 65.4 14.3 2.8 0.96 7.7 2.7 5.9
Black glaze 66.4 15.9 2.3 0.5 8.0 2.6 4.6
Kaki (russet) 70.7 17.1 2.7 1.2 3.7 2.2 2.4
Tea dust 68.1 18.5 2.5 1.8 3.3 2.6 3.2
The
glaze formulas were converted to gram weights.
The powdered materials were carefully weighed on a gram scale to make
100-gram test batches. Each batch was
then mixed with water to a creamy consistency and applied to an off-white,
extruded clay tile that had been bisque-fired to 871C/1600F. Each glaze was applied on a tile in three
layers to show thin, medium, and thick coatings. Varying the thicknesses is important, as it shows the depth of
the glaze as well as the quality of its melt.
All thirty tests were fired at cone 9, 1260C/2300F. The fired results were not good. The glazes were dry and matte, not smooth and
glass-like. And although they were
brown and dark green, there were no dark browns or blacks. I recalculated many of the glazes to see if
I had made a mistake, but my calculations were all accurate. What could be wrong?
When
I spoke with the technician who performed the analyses, I was told the accuracy
was +1/-1%. I had varied the tests
enough to make up for that. It was
possible, but unlikely,
that
the published UPA was wrong. The other
variable left was temperature. The
author of the catalog had mentioned that the Song glazes were fired between
1236C/2257F and 1294C/2361F, and I had fired my tests at 1260C/2300F. So it was possible I was at the low end of
the temperature range and the glazes were simply not mature. A higher temperature would be required. It also dawned on me that the large climbing
kilns used during the early Song Dynasty would take days to fire with wood. Perhaps the temperature was not hotter than
indicated, but rather the long time at that temperature (referred to as the
fire’s soak) would eventually melt the glazes.
My choices were to fire at a hotter temperature or to hold the kiln at a
lower temperature for a longer time.
Neither was a good solution, because my kiln will not fire hotter
without damage from the excessive heat and I was not prepared to spend hours
and hours trying for a longer soak.
My
solution was to recalculate the glazes so they would melt at a lower
temperature. The alumina oxide is the
highest-melting (i.e. melting at the highest temperature) oxide in a
glaze. I began lowering the alumina
oxide by 1-3% increments. I
recalculated fifteen of the original glazes with lower alumina oxide
contents. The dry materials for each
formula were weighed, mixed with water, applied to tiles, and fired. The results were a little better, but the
glazes remained dryish and dull.
I
recalculated the formulas again by lowering the alumina oxide contents
more. Again the dry materials for each
formula were weighed, mixed with water, applied to tiles, and fired. The results were much better, but the glazes
still were not glossy and smooth.
The
amounts of sodium and potassium oxides in my calculated glazes seemed low. So I raised the amounts of these oxides by
1% and 2%, holding the amounts of alumina oxide constant. The dry materials for each formula were
weighed, mixed with water, applied to tiles, and fired. These results were much better. All of the glazes were melted to some
degree, and some of the glazes were slightly shiny.
Early
on, I also considered the amount of calcium oxide to be very low. However, I initially assumed the high iron
oxide content would somehow offset the low calcium oxide content. When it did not, I recalculated the fifteen
glazes, varying the calcium oxide by 3% and 6% in each. The dry materials for
each formula were weighed, mixed with water, applied to thirty tiles, and
fired. The results were very
promising. Most of the glazes were very
glassy, and some actually melted off the tiles.
The
best glaze melts were those where the thickest applications showed a smooth,
glassy depth and stability without runs, showing some of the qualities of the
old glazes I had seen in museums and books.
The
blacks and dark browns I was looking for did not appear in these tests. My guess was that the iron oxide contents of
the published UPAs may be of a different type of iron oxide, because the
published UPAs indicated the iron oxide to be FeO, the pure oxide form. The analyses of my materials indicated the
iron oxide to be Fe2O3, a less pure form and
thus
not as powerful a colorant. I next
tried to increase the strength of my colorant by increasing the amounts of iron
oxide in the formulas. I recalculated
the ten best glazes, increasing the iron oxide contents in the brown glazes by
1% and 2%. I raised the iron oxide
contents of the dark green glazes by 4% to 6%.
I used the materials with the highest iron oxide content, which were:
·
The Dalles
clay
·
Othello
clay
·
cinders
·
clay from
my property, which appears very similar to the The Dalles clay
I
then left the amounts of alumina oxide, sodium and potassium oxides, and
calcium oxide the same as I increased the iron oxide amounts. The dry materials for twenty formulas were weighed,
mixed with water, applied to tiles, and fired.
The results were very successful, ranging from dark browns to almost
black-browns with very smooth, glassy surfaces. Of these, I selected five glazes that were the darkest. Three glazes were dark brown to black and
two were brown. The goal of my research
was to get two temokus (a variable brown and black glaze), one kaki (an
iridescent brown glaze), one tea dust (a brown-black glaze with green specks),
and one black glaze. With the exception
of the black glaze, I was very close to the glazes I was trying to
recreate.
I
experienced problems applying these glazes.
Although a glaze may be technically formulated, it also has an important
aspect that is physical: a glaze must be suspended so that the particles will
not settle out in the water. But if a
glaze becomes too suspended, it will not dry properly on a bisque tile or
pot. The problem I had was that the
glaze formulas were now very high in clay content, which was necessary for the
glaze colors. However, the test glazes,
when applied, would not dry quickly and cracked when finally dry. I decided I would have to calcine the dry
clay materials. Calcining usually means
firing the material to 871C/1600F, which reduces its plasticity and shrinkage. I calcined the materials and the result was
that the glaze instead settled too quickly and would not remain suspended long
enough to be properly applied. I tried
calcining the clays at a lower temperature to try and retain some of the
plasticity. After many attempts, I
found 621C/1150F to be right. There was
still some suspension, but the applied glaze dried quickly. I calcined
·
The Dalles
clay
·
Othello
clay
·
clay from
my property
·
cinders
to
621C/1150F and began further testing.
I
recalculated the darkest glaze with 1% to 6% increments of manganese dioxide to
move the glaze toward black.
I
was also interested in creating a “tea dust” glaze, usually a dark brown glaze
with green specks. One of my dark
glazes had a little of this quality.
This particular glaze was made with a coarse (not ball-milled) calcined
The Dalles clay that was accidentally added when I
ran
out of the properly processed material.
I thought the coarser material may have caused the green specks, so I
screened the The Dalles clay at 150 mesh, 120 mesh, 100 mesh, and 80 mesh, then
remixed the tests to see if it increased the green specks.
The
kaki glazes were recalculated increasing the alumina oxide by 1% to 3% in an
effort to change the surfaces. Another
set of kaki glazes was recalculated increasing the silica dioxide by 3% and 6%
in an effort to slightly dull the surfaces.
CHART 3: UPAS OF MY GLAZE
RESULTS
Brown to black
glaze (temoku) 66.7 12.5 1.46 3.2 7.2 1.3 7.4 -
Black glaze 62.7 11.4 1.4 2.9 8.1 1.2 7.8 4.5
Tea dust 63.4 13.0 1.5 3.4 9.0 1.47 8.2 -
Kaki (russet) 63.8 16.5 2.6 3.8 5.9 2.7 4.6 -
By
this time, it was late summer. School
was to start soon, and I decided to put further testing on hold so I would have
time to revisit some of the sites before the rains started. I needed to get larger quantities of the
best working materials to be able to finish this research.
The
materials I had most consistently used were
·
Othello
clay
·
The Dalles
clay
·
Pendleton
pumice
·
cinders
·
G-1
·
beach sand
·
Blodgett
syenite
So
I went back to
·
The
Dalles, where I gathered approximately two hundred pounds of clay
·
Pendleton,
where I gathered approximately two hundred pounds of pumice
·
Santiam,
where I gathered cinders
·
Mount
Ashland, where I gathered approximately two hundred pounds of G-1
·
the coast,
where I gathered approximately two hundred pounds of sand
·
Blogett
Peak, where I gathered approximately two hundred pounds of syenite
I
had already gathered sufficient quantities of Othello and Ukiah clays and did
not need to revisit these sites.
I
ran the hard rock materials through my jaw crusher and roller mill to reduce
them to approximately 1/8” particle size and stored the separate materials in large
metal garbage cans. I now had about
1400 pounds of raw materials which, for some time to come, would enable me to
make consistent tests and eventually, large quantities of glazes.
Throughout
the spring and summer, I had also been experimenting with local clays to
formulate a suitable clay body.
Clay-testing is somewhat different than glaze-testing in that there are
more physical considerations. For
instance, if the clay body shrinks too much, it will crack upon drying. Therefore, only 10-15% of shrinkage is
acceptable. Also, a clay body should
have a relatively low absorbency, ½-2½% when fired, which means it is water tight
and will not expand or contract significantly.
Expansion or contraction greater than that could cause the glaze to
craze and the pot to become fragile. On
the other hand, if the clay is too tight, with for example 0% absorbency, it
would be very glass-like and the pot could deform during firing. Finally, the clay body must be plastic, i.e.
workable in the wet stage, so it can be formed and not slump or collapse from
its own weight.
Over
the years, I have used local clays for my stoneware clay body, which has a very
dark brown color and a rough texture.
For the brown and black glazes, however, I wanted a much lighter,
tan-colored clay with a relatively smooth surface, similar to the clays of the
ancient dark-glazed pots I had seen in museums and books.
Several
of the clays I have found over the years tested well for physical properties
such as plasticity and shrinkage. All,
however, had up to 10% fired absorbency at cone 9.
The
main clay I intended to use for the new body was Elmira clay, a clay I have
used for twenty years. The clay deposit
is located approximately 3½ miles west of the town of Elmira. The raw clay is very sandy and must be mixed
with water to a thin consistency and poured through a 120 mesh screen to remove
the coarse sand. This process helps the
resulting clay be more plastic.
Another
clay, named Hobart Butte clay, gathered near Cottage Grove at Hobart Butte, is
a kaolinite and very light-colored after firing. Different from the Elmira clay, Hobart Butte clay is very hard
and will not slake down in water.
Therefore, it must be ground and ball-milled.
These
two clays, combined in various percentages, produced a clay body that was
light-colored and smooth after firing.
It was not very plastic, however, barely throwable, and too absorbent. The Ukiah clay I had used in my celadon
research on porcelains was a very plastic clay when ball-milled, so I tried
adding various percentages of it to the other two clays to increase
plasticity. I ended up adding 11% Ukiah
clay and now had a physical body suitable for wheel-throwing.
I
had the analyses of Elmira and Ukiah clays from previous research. I had found an analysis of Hobart Butte clay
in a 1938 Oregon State publication named Oregon
Clay Deposits. So with these three
clay analyses I hoped to calculate a clay body very similar in color and
absorbency to the analysis of the Song Dynasty clay that was published in Hare’s Fur, Tortoise Shell, and Partridge
Feathers. I could not calculate an
exact copy of the
published
body with my clays. The alumina oxide
in the Song Dynasty UPA was higher by 3% than any formula I could
calculate. This is because the Chinese
clays were probably all true koalins, and therefore high in alumina oxide, and
the Oregon clays I collected are mostly high in silica dioxide. 3% is an acceptable variation for a clay
body.
By
using a light granite rock I called MA-4 (I gathered it from Mount Ashland), I
was able to get the sodium and potassium oxides to within ½% of the Song
Dynasty UPA, assuring a low absorbency rate.
And finally, I was able to get the iron oxide content to within ¼% of
the Song Dynasty UPA, assuring a very similar color.
CHART 4: UPAS FOR NATIVE
MATERIALS USED IN CLAYS
Ukiah clay 71.25 19.74 1.4 0.53 1.12 0.05 1.7
Elmira clay 73.0 22.0 1.0 0.43 - - 1.3
Hobart clay 58.6 29.2 - - - - 2.0
MA-4 rock 75.0 15.4 8.0 1.3 1.22 - -
CHART 5: PUBLISHED UPAS OF SONG
DYNASTY CLAY BODY
Song Dynasty
clay body 70.4 25.5 1.2 1.0 - - 1.9
I
made ten test tiles of various calculations to test for shrinkage, absorbency,
and color. The resulting fired tests
showed one to be the best, having 14% shrinkage, ½% absorbency, and a light tan
color. I mixed up five pounds to test
the workability of the clay body. The
clay was a little short on plasticity, but workable. I felt that after the clay had aged for a month or so, giving all
particles a chance to hydrate, the clay would become more workable. So I mixed up twenty-five pounds of the clay
body to make extruded tiles for testing the glazes.
CHART 6: RECIPE AND UPAS OF MY
CLAY BODY
9.8 Ukiah clay 7.0 1.93 0.14 0.05 1.2 - 0.17
48.3 Elmira clay 35.3 10.6 0.48 0.21 - - 0.63
19.0 Hobart clay 11.13 5.5 - - - - 0.38
22.9 MA-4 rock 17.2 3.5 1.83 0.29 - - 0.34
100.0 UPA TOTALS 73.0 22.2 2.5 0.56 0.12 - 1.6
The
preparation of my clay is as follows:
·
the Elmira
clay is mixed with water to a thin slurry so it can be screened through a 120 mesh
screen
·
the Hobart
Butte and Ukiah clays are crushed to 1/8” particle size, then mixed with water
so they can be ball-milled for approximately 12 hours
·
the three
clays are stored separately in their wet states in lidded, plastic containers
·
to
accurately calculate a clay formula, it is necessary to determine the
wet-to-dry ratios for each clay material; to do so, a 100-gram amount of each
slurry is dried and the dry materials are weighed again; the weight differences
give each material’s ratio
·
using the
ratios, it becomes possible to weigh the dry ingredients of a formula without
having to dry each clay material, a lengthy and space-consuming process
·
using the
clay formula (or recipe), the three clay slurries are weighed and mixed
together
·
the MA-4
powdered rock is added in its dry state
·
all
materials are thoroughly mixed until the particles are evenly distributed
·
the
resulting slurry, referred to as slip, is poured out into plaster troughs or
batts that absorb the excess water, a process taking five to ten days
·
when the
clay is firm enough, it is removed from the batts and stored in plastic bags to
age for a minimum of three to four weeks
After
processing the clay in the above manner, it was extruded and cut into 150 tiles
to be used for glaze tests. The tiles
were allowed to air-dry for a week, then bisque-fired to 871C/1600F.
I
now proceeded to test the temoku, tea dust, kaki, and near-black glaze formulas
on the new clay tiles. The results of
the fire were very good. The glazes fit
the new stoneware clay nicely. The
glazes darkened slightly because of the iron oxide content of the new clay, but
they looked excellent nonetheless.
There are still tests to do – the tea dust and kaki glazes were not
quite right yet and I want to fine-tune the color and quality of the melt – but
I considered the main stage of my research completed at this time. In all, this stage took most of the year,
twenty-seven kiln firings or approximately 324 hours of firing, and
approximately 750 glaze and clay tests.
I
was surprised that my final glaze results very closely resembled the celadon I
had done before in terms of their chemistry.
In other words, the UPAs of my dark glazes and celadons were in the same
ranges of silica, alumina, sodium, potassium, and calcium percentages. The significant difference was the presence
of high amounts of iron, which of course causes the dark glazes’ colors. When I started the project, I was interested
in the relationship between iron and calcium, assuming that the iron would flux
more and thus the calcium, sodium, and potassium would be in lower
percentages. This assumption was quite
incorrect. The fact is that the iron
oxide within the 8-10% range does not increase the melt, its only effect is to give
color. To verify this in the latter
stages of my testing, I simply used a celadon glaze, which is a light
grey-green color containing ½% iron, and to this glaze I added 9½% pure
commercial iron oxide. The result was a
dark brown to black glaze with an almost identical quality of melt as the
celadon, proving that the iron contributed little to the melt. The intent of this project, however, was to
use native materials that contain
iron oxide, rather than adding pure iron oxide to a glaze.
Over
the coming years, I hope to find more information and analyses of Song Dynasty
dark glazes and I hope such glazes will eventually indicate why the published
UPAs were so different from my final glaze UPAs. Again, it could be due to temperature or, perhaps, the published
UPAs were inaccurate. Time will
tell. Regardless, I now have a complete
palette of dark native glazes that have the quality and colors I had hoped
for.
All
that remains to be done is to mix up large quantities of clay and glazes and
make and fire pots. However, the
processing of large quantities of clay needs to be done during dry and hot
months to leave enough time to properly dry and age the clay, so this stage of
the process will have to wait until the late spring and summer of 2003.
Following
are the recipes and UPAs of the brown to black glaze (temoku), the black glaze,
the tea dust glaze, and the kaki (russet) glaze that resulted from my research.