Replace talc with a nepheline syenite:dolomite mix in low fire white clay 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
Our new ultra-clear cone 04 transparent base glazes for 2021
Five Low Fire Base Clear Glazes: What is the Best Strategy?

This new mix is just as white and it is fitting commercial glazes. And we have two base glaze recipes that fit also, that means you can make your own transparent glaze (and color it with stains).


Project Name

Replace talc in low temperature white body

Project Codenumber

UnAssigned

Notes

Talc has always been the "accepted" way of making low fire white bodies. Mixtures of ball clay and talc produce the outstanding working, casting, drying and firing properties. Talc is the secret behind raising the thermal expansion to fit commercial cone 06-02 glazes. And this mix 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. Although the traditional talc mix is porous and has poor strength in the fired state, these factors are discounted 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".

However a major problem arose during 2021: Texas talc ceased production. North American industry initially looked toward other talcs, but they fire significantly darker or are also ceasing production. A climate of litigation seems to be the reason for the demise of this material. A Chinese talc is available, but unlike the Texas talcs, it is not asbestos-free. Fortunately it is possible to make a body that fires just as white and strong with zero-talc.

We did a series of tests blending Nepheline Syenite, silica and Dolomite to substitute for the 50% talc in our main recipe, L213. It turned out a 80:20 Nepheline:Dolomite mix produces a white-burning body that fits typical glazes. These materials are easily available to us (nepheline syenite is a Canadian material, if you are in the US consider using a white feldspar).

An interesting finding in our testing has been that popular transparent glazes are not transparent, they fire amber and significantly darken the color of the white body. Spectrum Glazes #700 Clear is by far the best glaze we have tested (out of 5 brands).

The base transparent recipes (shown here) are a good option if you can mix your own. Stains and opacifiers can be added to these to make any color or effect. For now, consider substituting one of these as your transparent, and continue to use all the commercial colored glazes (and tolerate possible crazing with them). Another factor: World-wide supply chain issues could affect availability of glazes you use, so knowing how to mix your own from scratch and adjust it to be a brushing glaze, dipping glaze or base coat, is not a bad thing! The proportions of water:powder that we use are shown. Go to https://digitalfire.com/article/98 for more information on getting started mixing your own.

If you are in production, you might want to consider using a terra cotta, for example our G4170B (plastic and casting versions both work very well). For a white surface use the matching engobe, L3685Z2. See the link above for more information. Terra cotta bodies fire to much better strength and glaze fit is much less of an issue. Terra cotta bodies are also less expensive and have excellent workability. And, by firing to cone 03-02 stoneware strength can be achieved.

Pictures

L213 vs. L4410R - Both PB001 Glaze cone 05

If you are thinking about using a different brand of talc (other than Texas talc), think again! The piece on the right is 50:50 ball clay:Montana talc (vs. 50:50 ball clay:Texas tac on the left).
Both of these are glazed with Duncan PB001.

L213 NS:Dolo 30:20

Code #

L4410L

Materials Amt Units
*KT1-4 Ball Clay 50.000 GM
Nepheline Syenite 30.000 GM
Dolocron 4013 (Dolomite) 20.000 GM
Additions Amt Units
Bentonite 3.000 GM

Total:103.00 (R)

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 a Nepheline Syenite/Dolomite blend could replace it.

This is the casting version of the body. If pieces are unable to pull away from the mold without cracking, add a tiny amount of bentonite to improve plastic strength (e.g. 0.5%). For use on a potters wheel at about 3% bentonite.

Talc is is a magnesia mineral and so is dolomite. Can a small amount of dolomite encourage the growth of cristobalite and increase the thermal expansion of a body the same way that talc does? This recipe appears to say yes! Initial glaze testing of this looked promising. Fired whiteness is amazing. We are stunned by the quality of pieces we have been able to produce with this using standard low fire Spectrum glazes. However, over time it became clear that crazing will eventually occur.

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

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

Our G3879C and G1916QL1 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.

A test run of the plastic version of this was made at Plainsman Clays August 2021.

Unless otherwise noted we generally use our C04PLTP firing schedule.

Dry strength appears to be lower than for a ball clay:talc mix.

Pictures

Spectrum 700 clear and 742 red on L4410L

Out-of-the kiln there is no crazing, results are stunning! However over a few weeks the glazes did craze.

K4410K (left), L4410L (right) - Cone 6

This body has another advantage over the talc version: Although it begins to warp at cone 6 (stoneware temperature), it is not brittle, fired strength is excellent. That means that it should survive to cone 4. Another things that the is remains porous if bisque fired to cone 02 or even 2. This

L4410K cone 03 with spectrum brush-on glazes

L4410K had a 35:15 nepheline:dolomite mix (to substitute for the 50 talc). Spectrum 742 dark red, 705 black, 700 clear. Out of the kiln there was no crazing but over a few weeks they did.

P6936 L213 test with original lab mix - test bars

Bars are fired from cone 6 (top right) down to cone 04 (bottom right).

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 93.77 93.46 34.01 40.5 1.0 6.2% 0.3% 19.1%
2 93.67 93.32 35.87 42.23 2.0 6.3% 0.4% 17.7%
3 93.38 92.95 35.78 42.23 3.0 6.6% 0.5% 18.0%
4 93.01 92.51 35.89 41.72 4.0 7.0% 0.5% 16.2%
5 93.18 92.76 35.51 40.3 5.0 6.8% 0.5% 13.5%
6 93.42 91.14 35.41 35.51 6.0 6.6% 2.4% 0.3%
7 93.38 93.21 35.81 42.71 6.0 6.6% 0.2% 19.3%
8 93.44 93.1 35.27 42.02 -4.0 6.6% 0.4% 19.1%
9 93.61 93.37 35.43 42.01 -1.8 6.4% 0.3% 18.6%
10 93.83 93.54 34.93 41.36 -.8 6.2% 0.3% 18.4%

SOLU - Soluble Salts

FIRE
1 nil

DFAC - Drying Factor

DFAC SOLD
1 A000 vlight

CLWC - Clay Water Content - Powder, Plastic

PUGW PUGD POW% PUG%
1 25.74 20.48 20.4%

LDW - LOI/Density/Water Content

WWGT DWGT FWGT H2O LOI DENS
1 13.03 10.56 8.97 19.0% 15.1%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="L213 NS:Dolo 30:20" id="201792" key="CqbLqPaN" date="2022-01-01" codenum="L4410L"> <recipelines> <recipeline material="KT1-4 Ball Clay" amount="50.000" tolerance="" unitabbr="GM"/> <recipeline material="Nepheline Syenite" amount="30.000" tolerance="" unitabbr="GM"/> <recipeline material="Dolocron 4013" lookup="Dolomite" amount="20.000" tolerance="" unitabbr="GM"/> <recipeline material="Bentonite" amount="3.000" unitabbr="GM" added="true"/> </recipelines> </recipe> </recipes>

Born: 2021-02-06, Modified: 2022-01-01 18:58:24

L213 40:10 Dolo/NS

Code #

L4410P

Materials Amt Units
KT1-4 Ball Clay (KT1-4) 50.000 GM
Dolocron 413 (Dolomite) 40.000 GM
Nepheline Syenite 10.000 GM

Total:100.00 (R)

Notes

*This makes a bold move, upping the Dolomite all the way to 40%.

This is looking promising! So far, Duncan, Spectrum and Mayco transparent glazes are not crazing! The Mayco and Duncan glazes need to be put on thicker (they almost seem to be absorbing into the body), the Spectrum one works normally. The Mayco and Duncan have a higher thermal expansion, so they will craze sooner, in fact the Duncan PB001 crazes when thick on L213 (50:50 ball clay:talc). That gives confidence that the 700 glaze should endure without crazing.

This body is working very well, it is the product of 15 more more previous test mixes and hundreds of glaze tests. The workability, whiteness, glaze fit, firing all seem to be good. It is surprising that a recipe like this could work and encouraging that we can make a product having no silica (quartz) or talc.

The one down side is a much higher porosity. An interested side effect of that is that this readily absorbs a sealer to make it water tight.

This has the potential of being valuable for decorative tile (since it has almost zero firing shrinkage the tiles will fire flat). The fired strength is excellent, even after just a bisque firing.

Comments

2021-11-09

Steve Davis at Aardvark says they are now selling their 60:40 Ball clay:Dolomite body, named CREME, and it fits all the glazes. They are using Dolomite D-307 from Salinas, California.

Here is the web page for their body:
https://www.aardvarkclay.com/products.php?cat=25

Pictures

L4410P - Mayco S2101, Duncan PB001, Spectrum 700

Fired cone 05. No crazing after weeks on any of them. The 700 glaze fires much whiter than the Duncan or Mayco on this body (it must be using a higher quality frit).

Spectrum 700 on L4410M, N, P, Q - Cone 05

No crazing out of the kiln on any of them (these of some of the many recipe tests we did before settling on the P version). This is a testament to how good of a glaze the Spectrum 700 is. It fires more transparent (therefore whiter) than the others and fits better.

L4410 after several days soaking in water

The water as wicked up the walls (between the glazed inner and outer surfaces). After several days there is no crazing with Spectrum 700 or L3879C.

L4410P at cone 05 with Spectrum coloured glazes

These are slip-cast pieces. We are getting very good results with all glazes tried. Spectrum 753 Bright Yellow, 746 Bright Purple, 706 Royal Blue, 743 Bright Red Inside: #700 Firing schedule was BTSG05, bisque was BTFB04. This body is trickier to deflocculate than the talc version, we are working on a procedure using Darvan and Sodium Silicate.

L4410P at cone 06 (back), cone 6 (front)

Engobe is AMACO velvet. This clay sags and warps at cone 6 yet does not bloat and still has good fired strength. These pieces are slip cast.

L4410P fired bars

From cone 6 and 5 (top) down to cone 06.

L4410P sealed and unsealed

The body has high porosity, but this has an advantage: It soaks up silicone sealer very well. The slip-cast piece on the left was sealed (you can see the surface sheen) and it is impermeable to water penetration (the glaze is not crazed so water cannot penetrate there either). The piece on the right soaks up water readily (on the lower unglazed portion). The porosity of the body has another advantage: It does not appear to be subject to moisture expansion (which would craze the glaze).

Bonding test of Spectrum 700 on L4410P

This GBBT test indicates a very good glaze-body interface.

Testdata

SHAB - Shrinkage/Absorption

DLEN FLEN FWT BWT CONE DSHR FSHR ABS
1 94.59 5.4%
2 94.59 95.57 33.47 42.97 2.3 5.4% -1.0% 28.4%
3 94.31 95.15 33.6 43.38 3.0 5.7% -0.9% 29.1%
4 94.12 94.7 33.01 41.89 4.0 5.9% -0.6% 26.9%
7 94.23 5.8%
9 94.46 95.17 33.52 42.92 -2.0 5.5% -0.8% 28.0%
10 94.69 94.85 34.22 43.88 -6.0 5.3% -0.2% 28.2%
12 94.57 5.4%
5 94.23 33.19 42.43 5.0 27.8%
6 88.04 33.01 36.92 6.0 11.8%
8 94.91 33.34 43.11 -5.0 29.3%

LDW - LOI/Density/Water Content

WWGT DWGT H2O LOI DENS
1 12.43 10.25 17.5%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="L213 40:10 Dolo/NS" id="208137" key="nJY8rZ6H" date="2022-01-20" codenum="L4410P"> <recipelines> <recipeline material="KT1-4 Ball Clay" lookup="KT1-4" amount="50.000" tolerance="" unitabbr="GM"/> <recipeline material="Dolocron 413" lookup="Dolomite" amount="40.000" tolerance="" unitabbr="GM"/> <recipeline material="Nepheline Syenite" amount="10.000" tolerance="" unitabbr="GM"/> </recipelines> </recipe> </recipes>

Born: 2021-10-28, Modified: 2022-01-20 16:59:50

Cone 05+ Lower Expansion glaze

Code #

G1916QL1

Materials Amt
Ferro Frit 3195 60.000
Ferro Frit 3249 25.000
New Zealand or Grolleg kaolin (Grolleg Kaolin) 10.000
45 micron Silica (Silica) 5.000

Total:100.00

Auto Unity Formula

CaO 0.51
MgO 0.28
Na2O 0.20
(KNaO) 0.20
B2O3 1.10
Al2O3 0.51
SiO2 3.03

Ratios

Si:Al: 5.9:1
SiB:Al: 8.0:1
R2O:RO: 0.2:0.8

Expansion

6.0 (Molar:6.0)

LOI

1.2

Notes

*This is a much-lower-thermal-expansion version of our standard G1916Q low fire clear recipe (which was delay-crazing on the L4410C, L4410K, L4410L cone 04 test bodies). The lower expansion was achieved by eliminating all high-expansion 3110 and more than doubling the low-expansion 3249. This now shivers on our L4170B terra cotta (use the G1916Q for it).

This also switches the ball clay for New Zealand kaolin, producing a much more transparent glass. And this is melting better (since frit 3249 is a very active flux).

The lower surface tension of this make it a better candidate than G3879 for opacification with zircon.

1500g powder, 1200g water produced a specific gravity of 1.49 and yield just over 1.80 litres. Sieving to 80 mesh was required to break down the kaolin agglomerates.

Comments

2021-09-11

Joe: August 12/21
1500 grams powder
1200 grams water.
Screened 80 mesh. S.G. 1.49
At this S.G. yield is just over 1.80 litres.
Glaze seems a little thick, maximum 5 second vigorous stir time to stettling after allowing to saturate overnight. Glaze falls off spatula very easily so am leaving here for Tony to evaluate. This glaze was difficult to screen at this S.G. but any more water and it might be too thin.

Joe: I am thinking if you want to properly assess glazes with New Zealand Kaolin in them that you have to screen the glazes first. This kaolin does not break down easily and you can see tiny dots of clay on the spatula when you stir glaze even after it is allowed to saturate overnight. Once screened 80 mesh, these agglomerations disappear.

Pictures

G3879C, G1916Q, G1916QL1 on L213 Cone 04

The move from ball clay to New Zealand kaolin (centre mug vs right mug) greatly improves the clarity (because of the reduction in iron and titanium).

Cone 04 G1916QL1 vs G3879C melt flow comparison

G1916QL1 is more melt fluid so it is likely useful before cone 04. But G3879C is also very fluid (it also has a higher surface tension). Both are producing textbook high quality flows.

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 was my favourite coffee mug. However it did finally craze after about 2 weeks of use (that motivated the recipe change to G1916QL1).

G3879C, G1916QL1 on L4410L Bisque 1800 glaze cone 04

No crazing after weeks of use, ultragloss. Frit 524 has much less iron, that is why that mug is so much whiter.

Testdata

SHAB - Shrinkage/Absorption

DLEN DSHR FSHR ABS
1 94.59 5.4%
2 94.59 5.4%
3 94.31 5.7%
4 94.12 5.9%
5 94.14 5.9%
6 93.92 6.1%
7 94.23 5.8%
8 94.13 5.9%
9 94.48 5.5%
10 94.69 5.3%
12 94.57 5.4%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 05+ Lower Expansion glaze" id="202545" key="w41yNMei" date="2021-10-01" codenum="G1916QL1"> <recipelines> <recipeline material="Ferro Frit 3195" amount="60.000" tolerance=""/> <recipeline material="Ferro Frit 3249" amount="25.000" tolerance=""/> <recipeline material="New Zealand or Grolleg kaolin" lookup="Grolleg Kaolin" amount="10.000" tolerance=""/> <recipeline material="45 micron Silica" lookup="Silica" amount="5.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2014-03-04, Modified: 2021-10-01 11:57:18

Cone 04 UltraClear Low-Expansion

Code #

G3879C

Materials Amt
Fusion Frit F-524 750.000 73.17%
Fusion Frit F-69 140.000 13.66%
New Zealand or Grolleg kaolin (Grolleg Kaolin) 90.000 8.78%
Silica 45 micron (Silica) 45.000 4.39%

Total:1,025.00

Auto Unity Formula

BaO 0.04
CaO 0.38
MgO 0.18
K2O 0.09
Na2O 0.10
(KNaO) 0.19
SrO 0.22
B2O3 0.74
Al2O3 0.47
SiO2 3.76

Ratios

Si:Al: 8.0:1
SiB:Al: 9.6:1
R2O:RO: 0.2:0.8

Expansion

6.2 (Molar:5.8)

LOI

1.1

Cost

2.73 per kg

Notes

*An adjusted version of G3879 to reduce thermal expansion. It switches the silica to 45 micron (325 mesh) for better dissolution in the melt. And it increases the frit low-expansion F-69 (the Fusion equivalent of Ferro 3249) at the expense of F-524.

This also switches to whiter burning kaolin (New Zealand), that improves transparency and removes the amber coloration.

It still fires to the same crystal clear. And is fitting pieces better, especially the L4410L body.

We mixed 1500g powder to 1125g water (57%/43%) to get a specific gravity of 1.54. This produced 1.7 litres.
After allowing to saturate overnight and screening to 80 mesh it worked well.

Comments

2021-09-06

Joe: August 12/21
Tried the same powder/water ratio as G3879B: 1500/1125 (57%/43%). SG 1.54. 1.7 litres.
Initial glaze was too thin, allowing to saturate overnight thickened it and a vigorous stir settled a 4-5 seconds. Screened 80 mesh,( a lot of material on screen for this amount of powder).
New Zealand Kaolin does not break down easily. Once screened 80 mesh, these agglomerations disappear.

2021-12-20

Joe Nov.24/21 Made a brush-on "gummed" version.
G3879C powder using "Grolleg" 500 grams
Tap water 250 grams
Laguna Gum Solution 100 grams
Was able to hand mix all powder into liquid blend and let sit for about half an hour and then screened 80 mesh in small talisman lab test sieve as small lumps could be seen which is probably the Grolleg Kaolin used in recipe. Yield was approx. 1 pint or 16 oz. and filled pint jar equal to spectrum pint jar to about the same level as the Spectrum #700 Clear glaze does when observing visually.
Lost a total of 39 grams glaze in process of screening and moving from container to container, so, actually even slightly more glaze than what is in a Spectrum jar.

2021-12-20

The jar of Spectrum #700 Clear has 666 grams of glaze.
The jar of Plainsman G3879C has 811 grams of glaze. So, this is just under 22% more glaze by weight and actually is that much if you take into account the amount lost during make-up of glaze. This glaze appears thicker when stirring alongside the Spectrum 700. Leave overnight to saturate and see if glaze thickens more. After sitting 5 days, glaze has not really thickened up and is a nice brushing consistency. Still appears to be slightly thicker than Spectrum 700 clear.

Pictures

G3879C is firing much whiter, why?

Cone 04. All three clear glazes are on the same body. Left to right: Amaco LG10, G3879C recipe, Crysanthos SG213. The middle one employs Fusion Frit F-524, it is more expensive. But look at the benefit: It fires much more transparent so the piece is much whiter. And it is not crazing or pin holing. And it is glossier.

G3879C, G1916Q, G1916QL1 on L213 Cone 04

The move from ball clay to New Zealand kaolin (centre mug vs right mug) greatly improves the clarity (because of the reduction in iron and titanium).

G3879C vs. G1916QL on L4410K low fire white

The iron from the ball clay is the reason the glaze on the right is off-white.

Cone 04 G1916QL1 vs G3879C melt flow comparison

G1916QL1 is more melt fluid so it is likely useful before cone 04. But G3879C is also very fluid (it also has a higher surface tension). Both are producing textbook high quality flows.

G3879C, G1916QL1 on L4410L Bisque 1800 glaze cone 04

No crazing after weeks of use, ultragloss. Frit 524 has much less iron, that is why that mug is so much whiter.

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 04 UltraClear Low-Expansion" id="202474" key="MYrHdnn1" date="2021-12-20" codenum="G3879C"> <recipelines> <recipeline material="Fusion Frit F-524" amount="750.000" tolerance=""/> <recipeline material="Fusion Frit F-69" amount="140.000" tolerance=""/> <recipeline material="New Zealand or Grolleg kaolin" lookup="Grolleg Kaolin" amount="90.000" tolerance=""/> <recipeline material="Silica 45 micron" lookup="Silica" amount="45.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2019-04-15, Modified: 2021-12-20 08:23:16