Terra Cotta clay from Ron Jarvis

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Grand Prairie clay: What needs to be added to it to bring plasticity down enough to make it dryable (without cracking), what temperature should it be fired at and what glazes will fit it at that temperature?


Grande Prairie Clay

Code #

L4254

Notes

He screened out the coarse particles and organic matter.

It is dark green in raw color (indicating high iron content).

This material is exceptionally plastic and smooth. With unbelieveably high drying shrinkage. Yet the test bars dried flat and did not crack. This is higly unusual.

The firing is not volatile, it matures progressively over a wide range. It thus has potential for stoneware at low temperatures.

It is clean, having no soluble salts. This is also very unusual for a terra cotta.

This needs to be mixed with a non-plastic filler. I would first try 60% of this and 40% feldspar. Fire it at cone 06,04,02,2,4. If a vitreous body is achieved at cone 02 (or more likely cone 2) then try a base clear glaze. For cone 2, try a glaze recipe of about 25% kaolin and 75% frit 3195 or 3124. If the glaze crazes, then change the body recipe to 60 red clay, 25 feldspar, 15 silica. For cone 02 use 20:80 glaze.

Comments

2020-04-22

From Mark Jarvis 780-518-6304

Pictures

Test bars prepared

Will fire to seven temperatures to profile fired shrinkage and density, color.

L4254 initial firing test to cone 6

This was done to guess the maximum firing temperature and melting behaviour. This is beginning to melt. There is no bloating or blistering, a very positive sign. And no sign of soluble salts.

L4254 fired bars

These bars are fired at 04,02,3,4 (bottom to top). The clean fired surface is exceptional. And the fired density is excellent and low temperatures. The material contains carbon volatiles that are creating gases during firing, these are causing the sample to litterally blow up like balloons. Strangely, the phenomena is not visible in the bar that was fired the highest? It must have blown up and then deflated! Also, the LOI is not high as would be expected. Items made purely from this would need to be thin walled. Mixing other materials with it would alleviate the issue.

Cone 5 bar - Melted but still in shape

When most raw clays melt, they bloat and bubble. But this one is a solid dense matrix, amazing. It was bonded to the kiln shelf so well we had to throw out the shelf (I manage to cleave away the upper half as shown here). It might sound crazy, but maybe this has application to ceramic-to-metal bonding. Or simply as a bonding clay (low melting plastic clays enable forming a product that holds together during production and they melt to glue the particles together in the kiln. We currently sell, by the semi-trailer-load, a low-melting clay-mineral-blend used for making corundum grinding wheels (the melting clay bonds the grains of alumina). This appears to be much better suited since it is pure, much more plastic and services at a lower temperature.

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 90.76 85.64 34.75 36.64 -2.7 9.2% 5.6% 5.4%
2 90.93 87.85 36.65 39.51 -4.0 9.1% 3.4% 7.8%
3 91.06 86.36 36.79 bloating -3.0 8.9% 5.2%
4 91.11 84.87 36.57 1.0 8.9% 6.8%
5 90.92 84.35 35.15 2.6 9.1% 7.2%
6 91.1 84.15 35.21 35.59 2.7 8.9% 7.6% 1.1%
7 90.97 84.88 34.56 34.71 4.0 9.0% 6.7% 0.4%

LDW - LOI/Density/Water Content

WWGT DWGT FWGT IWGT H2O LOI DENS
1 Cone 06 8.04 7.41 7.8% nang/cc
2 21.86 16.13 14.9 26.2% 7.6% nang/cc
3 cone 05 7.89 nang/cc
4 Cone04 8.44 7.81 1900F 7.5% 0.0g/cc
5 cone 03 9.39 nang/cc
6 Cone02 8.67 nang/cc
7 Cone01 8.75 nang/cc
8 Cone 1 8.77 nang/cc
9 Cone2 3.69 3.37 8.7% nang/cc

XML (to paste into Insight)

Born: 2019-12-17, Modified: 2020-06-29 10:34:04

Cone 1 Body Trial

Code #

L4254A

Materials Amt
*L4254 Clay 70.000
Nepheline Syenite 30.000

Total:100.00

Notes

This is still too plastic (drying shrinkage is too high). So it needs more non-plastic filler.

The fired color is very nice and it works well with the glaze (on the button).

Pictures

Cone 1 fired bar and glaze sample

Very encouraging result. The added feldspar has solved the bloating issue. The lower bar is exceptionally vitreous yet is stable. The glaze is G3806N1 with lavender stain. It seems to be working well.

L4254A fired bars

Cone 01,1,2,3 (bottom to top) Still to volatile. Cone 01 is too low, cone 1 is too high.

1916Q glaze on L4254A at cone 03

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 92.1 83.87 35.98 36.09 1.0 7.9% 8.9% 0.3%
2 92.22 83.74 35.91 35.91 2.6 7.8% 9.2% 0.0%
3 92.02 84.98 36.48 36.49 3.0 8.0% 7.7% 0.0%
4 92.22 84.61 37.59 38.61 -1.0 7.8% 8.3% 2.7%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 1 Body Trial" id="179123" key="i9QMgLa4" date="2020-09-16" codenum="L4254A" email="firebagmedx@gmail.com"> <recipelines> <recipeline material="L4254 Clay" amount="70.000"/> <recipeline material="Nepheline Syenite" amount="30.000"/> </recipelines> </recipe> </recipes>

Born: 2019-12-17, Modified: 2020-09-16 09:18:20

Cone 1 Body Trial 2

Code #

L4254B

Materials Amt
*L4254 Clay 70.000 63.64%
Silica 20.000 18.18%
Nepheline Syenite 20.000 18.18%

Total:110.00

Notes

This incorporates silica (it is a better filler for cutting plasticity). And it will help with glaze fit. And silica is more refractory than feldspar so this should have less fired shrinkage.

Working plasticity is a little low.

Pictures

L4254B at cone 2.5

Over-fired. Warping somewhat (rim is oval). Yet yellow glaze covers well (no bleed of iron from clay into glaze). Coverage of clear glaze on the inside (which has gone milky) is very good also. There was some glaze crawly, likely due to firing the piece while still wet from glazing.

L4254B fired bars

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 93.35 86.44 36.63 37.58 1.0 6.7% 7.4% 2.6%
2 93.41 86.14 38.58 38.79 2.6 6.6% 7.8% 0.5%
3 93.18 86.45 39.79 39.92 3.0 6.8% 7.2% 0.3%
4 93.18 88.31 warping 4.0 6.8% 5.2%
5 93.18 90.17 40.76 -3.0 6.8% 3.2%
6 93.25 87.48 41.14 -1.0 6.8% 6.2%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 1 Body Trial 2" id="179577" key="QD2zhZMc" date="2020-08-17" codenum="L4254B" email="firebagmedx@gmail.com"> <recipelines> <recipeline material="L4254 Clay" amount="70.000"/> <recipeline material="Silica" amount="20.000"/> <recipeline material="Nepheline Syenite" amount="20.000"/> </recipelines> </recipe> </recipes>

Born: 2019-12-17, Modified: 2020-08-17 14:34:36

Cone 1 Body Trial 2

Code #

L4254C

Materials Amt
*L4254 Clay 70.000
Silica 20.000
Nepheline Syenite 10.000

Total:100.00

Notes

Throwing is very good. Plasticity better than C. I was able to make a tall and thin walled piece on the potters wheel.

The drying shrinkage is still a little high so it will have to be dried carefully to avoid cracking.

Cone 04 bisque is too high, ware not porous enough.

Pictures

L4254C thrown cup

L4254C fired bars

Fired to (top to bottom) cone 2,1,01,02,03. Cone 2 is appears stable and very strong. Soluble salts on lower temperature bars. But cone 01 and 02 are low enough porosity that they would also make strong ware. But barium would be needed to precipitate the soluble salts.

L4254C fired mug - Cone 2

With G3806N2 clear and orange glazes. Inside glaze is under thermal expansion compression and forcing the piece apart.

L4254C mug - Cone 2

With G3806N2 clear and orange glazes. Glaze is crawling at the rim.

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 92.71 87.06 37.70 39.42 1.0 7.3% 6.1% 4.6%
2 92.56 86.13 39.72 41.23 2.0 7.4% 6.9% 3.8%
3 92.48 89.67 40.95 45.52 -3.0 7.5% 3.0% 11.2%
4 92.44 87.62 40.17 42.8 -1.0 7.6% 5.2% 6.5%
5 92.39 88.25 40.23 43.72 -2.0 7.6% 4.5% 8.7%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 1 Body Trial 2" id="179712" key="MJm5ibrb" date="2020-08-21" codenum="L4254C" email="firebagmedx@gmail.com"> <recipelines> <recipeline material="L4254 Clay" amount="70.000"/> <recipeline material="Silica" amount="20.000"/> <recipeline material="Nepheline Syenite" amount="10.000"/> </recipelines> </recipe> </recipes>

Born: 2019-12-17, Modified: 2020-08-21 11:29:12

Cone 1 Body Trial 3

Code #

L4254E

Materials Amt
*L4254 Clay 70.000
Calcium Carbonate 20.000
Silica 10.000

Total:100.00

Notes

This is a test to see whether these additions will cut the plasticity enough to make it useable.

This has not worked, the fired bars cone 02-1, but the drying shrinkage is still much too high. Silica was effective at cutting shrinkage in C. With test this at 20:20:60.

Pictures

L4254E Fired bars

These are looking a lot better than any previous tests with regard to their fired appearance and characteristics.

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 90.34 86.15 30.44 31.12 3.0 9.7% 4.6% 2.2%
2 89.96 87.95 31.87 35.42 -2.0 10.0% 2.2% 11.1%
3 90.04 86.32 30.7 31.65 3.0 10.0% 4.1% 3.1%
4 90.6 87.8 30.75 33.03 1.0 9.4% 3.1% 7.4%
5 91.04 88.16 30.93 32.81 2.0 9.0% 3.2% 6.1%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 1 Body Trial 3" id="182989" key="xTAPBLB3" date="2020-09-08" codenum="L4254E" email="firebagmedx@gmail.com"> <recipelines> <recipeline material="L4254 Clay" amount="70.000"/> <recipeline material="Calcium Carbonate" amount="20.000"/> <recipeline material="Silica" amount="10.000"/> </recipelines> </recipe> </recipes>

Born: 2019-12-17, Modified: 2020-09-08 11:16:11

Cone 1 Body Trial 4

Code #

L4254F

Materials Amt
*L4254 Clay 50.000
*Type F Fly Ash 50.000

Total:100.00

Notes

Fly ash has been a good plasticity-cutter in other projet. The drying shrinkage is acceptable. But plasticity is much too low. But it was very vitreous at cone 4, this is not cutting maturity enough.

Pictures

L4254F fired bars

Cone 6, 5, 1, 01 (top to bottom)

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 92.99 89.72 29.79 34.81 -4.0 7.0% 3.5% 16.9%
2 93.19 6.8%
3 93.41 88.48 27.71 31.03 1.0 6.6% 5.3% 12.0%
4 93.66 88.44 29.88 33.11 2.0 6.3% 5.6% 10.8%
5 93.64 88.19 30.57 33.07 5.0 6.4% 5.8% 8.2%
6 93.18 84.72 28.93 28.95 6.0 6.8% 9.1% 0.1%

LDW - LOI/Density/Water Content

WWGT DWGT H2O LOI DENS
5 19.55 14.01 28.3%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 1 Body Trial 4" id="183594" key="Sae8NWhX" date="2020-10-20" codenum="L4254F" email="firebagmedx@gmail.com"> <recipelines> <recipeline material="L4254 Clay" amount="50.000"/> <recipeline material="Type F Fly Ash" amount="50.000"/> </recipelines> </recipe> </recipes>

Born: 2019-12-17, Modified: 2020-10-20 17:23:46

Cone 1 Body Trial 5

Code #

L4254G

Materials Amt
*L4254 Clay 60.000
Calcium Carbonate 20.000
Silica 20.000

Total:100.00

Notes

This is looking very promising. Very low fired shrinkage at cone 04. Still high drying shrinkage, this might have to be tolerated.

Pictures

L4254F with clear glaze

The glaze is G1916Q. Temperature: Cone 03. This demonstrates the toll the needed additions (to cut plasticity) take on the fired color.

Untitled

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 91.5 91.27 32.52 37.51 -4.0 8.5% 0.3% 15.3%
2 91.6 90.93 34.27 38.81 -3.0 8.4% 0.7% 13.2%
3 91.68 91.09 33.84 38.5 -4.0 8.3% 0.6% 13.8%
4 91.42 8.6%
5 91.36 85.66 33.17 33.27 1.0 8.6% 6.2% 0.3%

LDW - LOI/Density/Water Content

WWGT DWGT H2O LOI DENS
1 20 14.92 25.4%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 1 Body Trial 5" id="183696" key="dzxFTydm" date="2020-11-05" codenum="L4254G" email="firebagmedx@gmail.com"> <recipelines> <recipeline material="L4254 Clay" amount="60.000"/> <recipeline material="Calcium Carbonate" amount="20.000"/> <recipeline material="Silica" amount="20.000"/> </recipelines> </recipe> </recipes>

Born: 2019-12-17, Modified: 2020-11-05 12:16:28

Cone 1 Body Trial 4

Code #

L4254H

Materials Amt
*L4254 Clay 50.000
Silica 20.000
Calcium Carbonate 20.000
*Silica Sand F75 10.000

Total:100.00

Notes

Pictures

Fired cone 03, 05 with G1916Qv2 glaze

Glaze at cone 03 has more microbubbling, indicating there is decomposition occurring in the clay (and generating gases). The cone 05 glaze is flawless. This was slow cooling but not drop-and-held during firing.

Untitled

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 92.8 92.63 34.33 39.99 -4.0 7.2% 0.2% 16.5%
2 92.92 92.58 35.32 40.84 -3.0 7.1% 0.4% 15.6%
3 92.83 92.43 37.1 42.62 -2.0 7.2% 0.4% 14.9%
4 92.83 7.2%
5 92.74 87.26 37.37 38.41 1.0 7.3% 5.9% 2.8%
6 92.52 86.95 36.9 37.72 2.0 7.5% 6.0% 2.2%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 1 Body Trial 4" id="183360" key="XSzbZoiK" date="2020-11-05" codenum="L4254H" email="firebagmedx@gmail.com"> <recipelines> <recipeline material="L4254 Clay" amount="50.000"/> <recipeline material="Silica" amount="20.000"/> <recipeline material="Calcium Carbonate" amount="20.000"/> <recipeline material="Silica Sand F75" amount="10.000"/> </recipelines> </recipe> </recipes>

Born: 2019-12-17, Modified: 2020-11-05 12:14:34

SiC bonded with L4254

Code #

L4355

Materials Amt
*L4254 6.600 18.03%
*Silicon Carbide 400 30.000 81.97%

Total:36.60

Notes

10% clay Plasticity is zero. Only able to form a button out of wet gooey material.
Fired at cone 6 it is not durable enough for use as a knife sharpener. It powders during grinding.

But at 20% it was much better. Still difficult to form but acceptable for machine pressing.

Pictures

10% clay at cone 6

Surface not durable enough. Under a microscope there does not appear to be enough bonding material.

20% clay fired at cone 6

This is much better. Feels similar to a typical grinding stone. The flat size can be used to sharpen a knife. However it can be scratched with a knife and it wears away as a brown powder. Slightly more clay is still needed.

Testdata

SHAB - Shrinkage/Absorption

DLEN DSHR FSHR ABS
1 97.45 2.6%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="SiC bonded with L4254" id="183953" key="maPDAZqZ" date="2020-10-15" codenum="L4355"> <recipelines> <recipeline material="L4254" amount="6.600"/> <recipeline material="Silicon Carbide 400" amount="30.000"/> </recipelines> </recipe> </recipes>

Born: 2020-09-14, Modified: 2020-10-15 10:55:25