Replacing Talc with Nepheline Syenite or Dolomite in Cone 04 White Bodies

Share from Insight-live.com (Lab Documentation and Calculation System) by Digitalfire.

See Also:
Cone 04 Terra Cotta Casting/Throwing Body, Transparent Glaze, Firing Schedule

Is this even possible? Yes. The bodies are as white or whiter, plasticity is the same, shrinkage and maturity also.


Project Name

Nepheline Syenite low temperature white body

Project Codenumber

UnAssigned

Notes

This is a project to make a major change to our thinking about this type of body. Talc has always been the "accepted" way of making these bodies. Mixtures of ball clay and talc produce the outstanding working, casting, drying and firing properties that make this usable by hobbyists. Talc is the secret behind raising the thermal expansion to fit commercial cone 06-02 glazes. And the magic mix with ball clay creates fantastic plastic working properties (and casting). Until now, in North America, talc and ball clay grades could be selected to produce a very white burning body. Actually, that is not quite true, only ball clays could be selected (only one talc was white enough: Texas talc).

However a major problem arose during February 2021: Texas talc, named C-98, is no longer available. Now we are faced with using talcs, that although are much whiter in the raw form, and on paper appear to be just as low in iron, in practice fire significantly darker. And they are not as effective at increasing body expansion as C-98. For a long time we have wanted to stop using talc, mainly because it makes powder handling and pugging of bodies so difficult. Now, the climate of litigation that surrounds it greatly increases our motivation to stop using it in these types of bodies. This is going to cause some pain, but it seems necessary.

Whiteness is very important. These bodies exist mainly because they are white. They are highly porous and have poor strength in the fired state, but these properties are conveniently ignored in order to provide hobbyists and artware producers a white "canvas" on which to apply colorful glazes! That means the dark-burning talcs are "non-starters".

Our testing program revealed some surprising things and motivated us to do testing we would not have otherwise done. The surprising result that that a 35:15 Nepheline Syenite:Dolomite mix substitutes for the 50% talc in our main recipe, L213, to produce a whiter body of equal working properties. And the glazes fit! It is an understatement to say how ecstatic we are over this result! Since Nepheline Syenite is a Canadian material, it is a double-bonus for us.

Like the old talc bodies, this one becomes brittle and begins to fail around cone 4. However, although our initial 50:50 trial mixes of ball clay and nepheline (without the dolomite) turned out not to fit common cone 06 glazes, we found that these could be fired as high as cone 2 and low fire glazes produced stoneware on them (without crazing). Even at cone 03 it was easy to mix our own glazes that fit. And, the 50:50 body even fired to cone 6, using cone 6 glazes, to produce highly vitreous and super strong ware ivory porcelain.

Low Fire White Nepheline Syenite body

Code #

L4410C

Materials Amt
KT1-4 50.000
Nepheline Syenite 50.000
Additions Amt
Bentonite 3.000

Total:103.00

Notes

*L213 is a body made by Plainsman Clays, it has traditionally employed Texas talc and KT1-4 ball clay, a simple 50:50 mix. This is part of a project to explore the possibility that Nepheline Syenite could replace it.

We have been impressed by the workability of this nepheline:ball clay mix. It works physically in both the plastic form (this one) and the casting version (with 1% bentonite).

At cone 04 this crazes commercial glazes that worked on the talc version. At cone 03 and 02 they fit better (I am adapting G1916Q and G3879 clear recipe to fit better).

A huge advantage of this body recipe is that it fires more and more vitreous toward cone 6 and even beyond, achieving stoneware strength and density starting around cone 3 (whereas talc bodies degrade at higher temperatures). Amazingly the G1916Q works well at cone 2 and even above. And G2926B cone 6 clear works well from cone 4-5 and up.

The advantages of this mix are so great that we are highly motivated to adapt glazes to it at low fire. We did try silica additions to fit the glazes better but abandoned the idea.

Pictures

IMG_7859

L4410C casting with 1% and 0.5% bentonite

With 0.5% bentonite many of the rim corners were breaking off during casting, demolding and dry finishing. Increasing to 1% completely solved the problem without increasing casting time too much.

G3879G2 on L4410C Cone 04, 03, 02

At cone 04 semi glossy. And badly crazed. Cone 03: Super glossy, crazed after a month. Cone 02: Super glossy, no crazing for a 2 months. It has very good fired strength, shattering like a porcelain.

L4410C with G1916QL glaze

Fired cone 06, 03 After a couple months both are crazing about the same amount. Another piece at cone 02: Slight crazing after two months

L4410C with G1916Q glaze

Fired cone 1, cone 03 After a month cone 03 is crazing, cone 1 is not.

L4410C with G3879G1 cone 04, 03

Both excited kiln craze free After two months both are crazing.

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 93.07 92.01 36.92 42.33 -6.0 6.9% 1.1% 14.7%
2 93.24 90.75 37.31 41.59 -4.3 6.8% 2.7% 11.5%
3 93.3 89.83 37.63 41.21 -2.5 6.7% 3.7% 9.5%
4 93.32 89.06 38.76 41.61 -2.0 6.7% 4.6% 7.4%
5 92.98 87.01 38.05 39.44 1.8 7.0% 6.4% 3.7%
6 93.01 86.32 37.67 38.46 3.0 7.0% 7.2% 2.1%
7 94.45 89.09 38.13 39.97 -1.0 5.6% 5.7% 4.8%
8 94.31 88.63 38.9 40.37 1.0 5.7% 6.0% 3.8%
9 94.27 87.63 38.56 38.67 4.0 5.7% 7.0% 0.3%
10 94.12 87.31 39.4 39.42 5.0 5.9% 7.2% 0.1%
11 93.98 86.81 38.95 38.96 6.0 6.0% 7.6% 0.0%
12 93.80 86.98 39.15 39.17 6.8 6.2% 7.3% 0.1%
13 93.88 87.84 8.0 6.1% 6.4%

SOLU - Soluble Salts

FIRE
3 nil

DFAC - Drying Factor

DFAC SOLD
1 A000 LITE+

CLWC - Clay Water Content - Powder, Plastic

PUGW PUGD POW% PUG%
1 30.37 24.16 20.4%

LDW - LOI/Density/Water Content

WWGT DWGT FWGT H2O LOI DENS
1 17.34 15.85 12.2 8.6% 23.0%
2 17.34 13.22 23.8%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Low Fire White Nepheline Syenite body" id="191679" key="iYfgJ15q" date="2021-06-24" codenum="L4410C"> <recipelines> <recipeline material="KT1-4" amount="50.000" tolerance=""/> <recipeline material="Nepheline Syenite" amount="50.000" tolerance=""/> <recipeline material="Bentonite" amount="3.000" added="true"/> </recipelines> </recipe> </recipes>

Born: 2021-02-06, Modified: 2021-06-24 18:23:29

Low Fire White NS/Dolomite Body 2

Code #

L4410K

Materials Amt
KT1-4 50.000
Nepheline Syenite 35.000
Dolocron 4013 (Dolomite) 15.000
Additions Amt
Bentonite 3.000

Total:103.00

Notes

*Can a small amount of dolomite encourage the growth of cristobalite and increase the thermal expansion of a ball-clay-based low temperature body the same way that talc does? This recipe appears to prove that the answer is yes!

Initial glaze testing of this is looking very promising. Fired whiteness is amazing, quite a bit whiter than our former L213 talc:ball clay mix. We are stunned by the quality of pieces we have been able to produce with this using standard low fire Spectrum clear glazes. Used in functional ware it appears crazing will eventually occur in ware fired at cone 04 (using Spectrum glazes). There is possibility they will perform better at cone 06.

Plasticity and workability is also as good or better than the former talc body.

An real plus is that this body employs Nepheline Syenite as a filler, instead of quartz. That makes it even safer to use.

Our G3879G1 and G1916QL glaze recipes are working well on this. That means the suppliers and users can make these as dipping glazes for functional surfaces (or as bases for additions of color and opacifiers).

Pictures

L4410K with G1916Q, G3879, G3879#2, G1916QL cone 04

Without looking at the base any of these could be mistaken for a high fire porcelain with clear glaze! G3879#2 with slow-heated and slow-cooled through cristobalite inversion during bisque.

L4410K cone 03 with spectrum brush-on glazes

Spectrum 742 dark red, 705 black, 700 clear. Out of the kiln there was no crazing.

Spectrum 700 clear on L4410K at cone 04 crazed after two week of use

This was used for coffee. The crazing appear suddenly one day, I am suspicious it related to a hot-to-cold sudden temperature change.

Spectrum 705 Black, G1916QL clear on L4410K at cone 03

The quality of this piece is amazing! The evenness of coverage that can be achieved with brush-on glazes is impressive. This is my favourite coffee mug now!

By cone 6 L4410K is bloating and warping

L4410K with G3879G1 and G1916QL at cone 04

Both are crystal clear, results are stunning! Both the G3879G1 and G1916QL glazes are holding up well in my kitchen at home.

L4410K cone 04 Spectrum reds

Left: 742 Dark Red, right 748 Fire Engine Red Insides: G1916QL, G3879B right (the latter is significantly whiter) The 1916QL began to spiral craze on the inside after a couple of weeks using in our kitchen.

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 93.72 93.17 37.16 43.7 -6.0 6.3% 0.6% 17.6%
2 93.63 92.82 37.66 43.99 -4.0 6.4% 0.9% 16.8%
3 93.6 6.4%
4 93.65 92.66 36.42 -2.0 6.3% 1.1%
5 93.69 6.3%
6 93.74 92.84 36.44 42.35 1.0 6.3% 1.0% 16.2%
7 93.78 92.71 36.06 41.79 2.0 6.2% 1.1% 15.9%
8 93.6 92.52 36.91 42.59 3.0 6.4% 1.2% 15.4%
9 93.64 92.29 35.52 40.1 4.0 6.4% 1.4% 12.9%
10 93.55 91.62 35.57 38.04 5.0 6.5% 2.1% 6.9%
11 93.6 90.97 33.71 33.77 6.0 6.4% 2.8% 0.2%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Low Fire White NS/Dolomite Body 2" id="198855" key="eqmZpR5q" date="2021-07-11" codenum="L4410K"> <recipelines> <recipeline material="KT1-4" amount="50.000" tolerance=""/> <recipeline material="Nepheline Syenite" amount="35.000" tolerance=""/> <recipeline material="Dolocron 4013" lookup="Dolomite" amount="15.000" tolerance=""/> <recipeline material="Bentonite" amount="3.000" added="true"/> </recipelines> </recipe> </recipes>

Born: 2021-02-06, Modified: 2021-07-11 11:39:01

Cone 06+ Low Expansion Transparent glaze

Code #

G1916QL

Materials Amt
Ferro Frit 3195 65.000
Ferro Frit 3249 20.000
No. 5 Ball Clay 15.000

Total:100.00

Auto Unity Formula

CaO 0.54
MgO 0.23
Na2O 0.22
(KNaO) 0.22
B2O3 1.10
Al2O3 0.54
SiO2 3.04

Ratios

Si:Al: 5.6:1
SiB:Al: 7.7:1
R2O:RO: 0.2:0.8

Expansion

6.1

LOI

1.4

Notes

*This is a lower-thermal-expansion version of our standard G1916Q low fire clear recipe (which was delay-crazing on the L4410C at cone 04 clay).

The original recipe was 65:10:10 of Frit 3195:3110:3249. This one trades all the high-expansion 3110 for low expansion 3249. Fitting this to the L4410C is a matter of testing from cone 04 and up until a temperature is reached where the glaze does not craze. This even shivers on our L4170B terra cotta, so the thermal expansion is certainly lower.

This is melting better and producing dazzling ultra clear results! One reason that it melts so well might be that the recipe contains no silica (although the SiO2 is still good).

Equal parts of water/powder seem to create a pleasant slurry that does not settle.

Pictures

G1916QL on L3685Z2 on L4170B at Cone 04, 02

After months both are still uncrazed. But some shivering on the rim of cone 02 piece.

L4410K with G3879G1 and G1916QL at cone 04

Both are crystal clear, results are stunning! Both the G3879G1 and G1916QL glazes are holding up well in my kitchen at home.

Spectrum 705 Black, G1916QL clear on L4410K at cone 03

The quality of this piece is amazing! The evenness of coverage that can be achieved with brush-on glazes is impressive. This is my favourite coffee mug now!

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 06+ Low Expansion Transparent glaze" id="192370" key="pESNQxpF" date="2021-07-06" codenum="G1916QL"> <recipelines> <recipeline material="Ferro Frit 3195" amount="65.000" tolerance=""/> <recipeline material="Ferro Frit 3249" amount="20.000" tolerance=""/> <recipeline material="No. 5 Ball Clay" amount="15.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2014-03-04, Modified: 2021-07-06 08:16:43

Cone 04+ Super Low Expansion Transparent

Code #

G3879G2

Materials Amt
Fusion Frit F-524 65.000
Fusion Frit F-69 20.000
Silica 325 (Silica) 15.000
Additions Amt
VeeGum 1.000

Total:101.00

Auto Unity Formula

BaO 0.03
CaO 0.35
MgO 0.26
K2O 0.07
Na2O 0.09
(KNaO) 0.16
SrO 0.20
B2O3 0.81
Al2O3 0.35
SiO2 4.15

Ratios

Si:Al: 11.9:1
SiB:Al: 14.2:1
R2O:RO: 0.2:0.8

Expansion

5.8

Cost

2.42 per kg

Notes

*This is a lower thermal expansion version of our G3879 clear glaze (which was reverse engineered from a commercial product that we like). That means it will be less likely to craze on the white-burning body we are developing cone low temperature (to replace the form talc:ball clay mix).

Mixed 500 water with 500 powder. Stops moving on mixer stop in about 3-4 seconds. But feels very thin. Yet applies evenly at normal thickness. Does not appear to settle (even though it contains no kaolin or ball clay!)

Has much higher SiO2:Al2O3 ratio to make it more glossy.

At cone 04 on L4410C it was semi glossy. And badly crazed. But it should fit the L4410K.

Pictures

G3879G2 on L4410C Cone 04, 03, 02

At cone 04 semi glossy. And badly crazed. Cone 03: Super glossy, crazed after a month. Cone 02: Super glossy, no crazing for a 2 months. It has very good fired strength, shattering like a porcelain.

G3879G2 on L4115L2A cone 02 - No crazing after months

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 04+ Super Low Expansion Transparent" id="194906" key="boaYRbK1" date="2021-07-06" codenum="G3879G2"> <recipelines> <recipeline material="Fusion Frit F-524" amount="65.000" tolerance=""/> <recipeline material="Fusion Frit F-69" amount="20.000" tolerance=""/> <recipeline material="Silica 325" lookup="Silica" amount="15.000" tolerance=""/> <recipeline material="VeeGum" amount="1.000" added="true"/> </recipelines> </recipe> </recipes>

Born: 2021-03-08, Modified: 2021-07-06 10:09:03