Cone 6 Grolleg translucent porcelain for throwing, casting, 3D printing

Project Name

A cone 6 Grolleg plastic/casting porcelain

Project Codenumber

UnAssigned

Notes

This page is about making your own translucent plastic porcelain (for throwing or 3D printing). Veegum is the secret to the plasticity. The casting version recipe shown here is demonstrates the recipe adjustments needed to change the body from plastic to casting.

White porcelains are made from kaolin, feldspar and silica - white stonewares use a mix of kaolin and ball clay to mix with the feldspar and silica (note we are using Nepheline as the feldspar). Cone 10 and 6 porcelains vary in the amount of feldspar needed (5-10% more at cone 6, at the expense of the clay). Kaolins are not plastic enough for either throwing or casting bodies, so bentonite is added. For casting, ~1%, for throwing up to 5%.

The very whitest porcelains are made using New Zealand kaolin (e.g. Plainsman Polar Ice). However, in the L3778G here we use Grolleg kaolin because it is easier to get. For NZK use it at 42%, 200 mesh silica at 20%, 270 mesh Nepheline at 35% and Veegum at 3-4% for maximum plasticity (or 1% for casting).

Note that the 2% Veegum increase in the D recipe enables a 10% drop in the nepheline without losing firing maturity!

Assuming that 20-25% silica is needed for glaze fit, we did a series of tests (L3778) to discover what blend of feldspar and kaolin (in the remaining 75% of the recipe) is needed to achieve a degree of vitrification where zero porosity is reached a little before the intended temperature.

As you will see from these results, VeeGum is a truly remarkable material. It has unparalleled plasticizing power, fires completely white and is an amazing flux. For plastic bodies (not casting) 3% VeeGum is enough to get good plasticity, 4% will give superplasticity (if you can afford it, can tolerate how much more difficult it is to slurry up, more water and increased drying shrinkage). Note: If you reduce the Veegum to 1% to make a casting version of this body, it will fire less mature, less vitrified.

This recipe is also great for adding stains. But keep in mind that stains can affect the fired shrinkage. Notice we have fired samples at many temperatures and measured the shrinkages to confirm compatibility between the blue and pink at cone 6.

If is possible or even likely that your application might require tuning the maturity. For example, if pieces warp during firing, reduce the feldspar in favor of kaolin to adjust. If pieces are firing well and more translucency is needed, increase the feldspar at the expense of kaolin. If more plasticity is needed, increase the Veegum.

If you would like to use a commercial translucent body instead Stephanie Osser recommends Glacier White S3128 (from lagunaclay.com, they describe it as being translucent from 1/8 to 1/4 inch thick from cone 5–8, total shrinkage is 14.5%). Plainsman Clays also has both casting and plastic versions of Polar Ice. And Southern Ice is also an option.

URLs

How to make a porcelain

Every potter needs a plaster table

Convert a Grolleg throwing body to a casting body

Pictures

Grolleg Polar Ice vs. NZK Polar Ice

The Grolleg version fires a little darker, this because its iron content is a little higher. But also because it has 7% more kaolin in the recipe (it requires less feldspar). These are thrown pieces, but both of these can be made into a casting body by changing the amount of bentonite in the recipe (from 4% to 1%).

Cone 6 Translucent Grolleg Plastic

Total:100.00

Auto Unity Formula + Analysis

Notes

*The objective of this recipe is a compromise between a vitreous body that fires translucent and one that is not so vitreous that functional pieces warp in the kiln. The previous mix, L3778C, had 25 Nepheline Seynite but mugs pulled oval on the rims (from the weight of the handles) during firing. This reduces the nepheline to 20 (and also the VeeGum to 3). This amount of nepheline makes the body reach the density of zero porosity between cone 5 and 6.

Throwing and trimming are fairly good, but are even better with 4% VeeGum (if the stickiness can be tolerated that is definitely. more plastic). Veegum is not only a plasticizer, but it is a super-flux, without if much more nepheline is needed.

The Veegum in the recipe changes the mixing procedure. Much more water is required to slurry up the recipe and it will take much longer to dewater on the plaster table. For 3D printing more Veegum might be desirable (for better stickiness and plastic strength).

The drying shrinkage is remarkably low.

Pictures

Translucency of Polar Ice (left) vs. L3778D

This is in sunlight. It might seem logical that the casting version of this body, L3778G, would be more translucent because it has 10% more nepheline syenite. But that is not the case, the translucency of this body comes mainly from the Veegum. Added 1%, to make a total of 4%, will further improve translucency.

Grolleg Polar Ice vs. NZK Polar Ice

The Grolleg version fires a little darker, this because its iron content is a little higher. But also because it has 7% more kaolin in the recipe (it requires less feldspar). These are thrown pieces, but both of these can be made into a casting body by changing the amount of bentonite in the recipe (from 4% to 1%).

L3778A to D fired bars

Bars from 5 different tests at cone 8.
A is 30% nepheline and 25 silica, way too vitreous, even at cone 6.
B is10 nepheline, 10 Frit 3110. Too dark, the frit is highlighting the iron.
C is 25 nepheline, 25 silica. It is expanding by cone 6 also.
D is only 20% nepheline and 25 silica better. And also best whiteness.

3778A-E fired bars

Cone 5 (left), cone 8 (right)

Plainsman Polar Ice vs. L3778D Grolleg Porcelain

L3778D vs L3778F Fired bars

From cone 3 (top) to cone 9.
The D is definitely more vitreous (see porosity and shrinkage data below).

Cone 6 Translucent Grolleg Casting

Total:100.00

Notes

*Because this employs Grolleg kaolin, it fires much whiter than bodies made using North American kaolins. And it will be more vitreous.

Substituting New Zealand kaolin for Grolleg Kaolin will whiten the body, but if you use it be ready to adjust the percentage of Nepheline to control changes in degree of vitrification. Plainsman Polar is made this way. It has 4% Veegum and 25% silica, so deriving the nepheline/NZK ratio is just a matter of testing to determine the best compromise between highly vitrified and resistance to warping in the kiln (nepheline with be between 20 and 30%, the nepheline/kaolin combination should total 74).

The 1% VeeGum is needed for casting, without it the clay shrinks too little and lacks the leather hard strength to pull itself away from the mold.

You can convert this to a plastic throwing version by simply adding more VeeGum. It has unparalleled plasticizing power, fires completely white (but its addition can drastically reduce the amount of feldspar/nepheline needed, Veegum is a superflux). For plastic bodies 3% VeeGum is enough to get good plasticity, 4% gives super plasticity.

For slurry-mixing instructions use the ones found on the Polar Ice data sheet at plainsmanclays.com.

Pictures

L3778G cone 6 Grolleg casting body vs. others

Top is this body.
Next one is a whiteware casting body made using Pioneer Kaolin and KT1-4 ball clay (M370 casting)
The bottom one is a buff stoneware (M340 casting)

L3778G Grolleg cone 6 casting

The glaze is GA6-B. The body fires extremely white and dense, producing stunning pieces. It is porous at bisque state and it is easy to get glazes on too thick.

L3778G with GA6-B glaze fired at cone 6

Fired strength is very good (under the hammer). Rather than shatter, it simply broke cleanly into to pieces.

L3778G Cone 6 Translucent Grolleg Casting fired bars

L3778G vs Polar Ice - Fired bars