Alternate Names: Veegum T, Veegum CER, Veegum Pro, VGT
Veegum, or VeeGum T (or VGT) is not a 'gum', rather it is a refined fine particle mineral called 'smectite' (bentonite and hectorite are members of the smectite group). It is a complex colloidal and extremely plastic and sticky magnesium aluminum silicate. It is an off-white insoluble flaky consistency and swells to many times its original volume when added to water. Its aqueous dispersions are thus high viscosity thixotropic gels at low solids. A potter encounters this phenomenon when employing significant percentages of VGT in glazes and porcelain bodies (e.g. more than 2%), finding that much more water is needed to produce a pourable suspension. Veegum is not subject to attack by microorganisms. Various grades are classified according to viscosity and ratio of aluminum to magnesium content.
Density (Mg/m3): 2.6
Viscosity (after shear mixing, 5% dispersion): 250 cps +/- 25%
Moisture: 8% max
The manufacturer says it is important to properly hydrate the powder, mix it in water before adding other ingredients (different grades of Veegum hydrate at different rates). They emphasize not underestimating the time needed, pointing out that in 25C water it could take 120 minutes using a propeller mixer! Using hot water or a higher energy mixer can drastically cut the time needed. If you are unable to mix the Veegum-containing slurry for the necessary time you can simply use a great percentage (however keep in mind that this is a very expensive material). It is important to use the same water temperature, mixing time and energy and viscosity each time it is used to get consistent behavior in the slurry or pugged material.
In glazes VGT is used as an in-mix suspending agent and surface hardener. It is also suitable for use as a spray-on surface hardener before decorating (mix it with water and put a light layer on dried ware). Be careful not to use too much, even 0.5% can gel the slurry having existing but insufficient clay, (start with 0.2% for testing).
In bodies VGT is employed as a plasticizing agent. It is a nonmigrating binder because it is not dissolved in the water. Its key advantage is that it is clean and therefore does not affect fired whiteness. 1.5-2.0% added to a porcelain, that is otherwise a little to short for modeling or throwing, will transform it into a plastic material. Amazingly, VGT can plasticize completely nonplastic materials (such as calcined alumina, zirconia, calcium carbonate, magnesium carbonate, dolomite) at only 3-4%! White burning porcelains are low-plasticity by nature, but VGT in higher percentages (up to 4%) can produce fantastic plasticity and workability. VGT may produce more plasticity in one body than another, depending on the type of kaolin present and the particle dynamics of the mix. For some formulations it is difficult to produce the needed plasticity without ending up with a body that is too sticky or requires too much water.
Veegum CER is a mixture of Veegum T and medium viscosity sodium carboxymethylcellulose that gives optimum surface hardening of unfired ceramic glazes for safe handling of the ware. It serves as hardener, suspending agent and viscosity stabilizer in glazes.
Veegum Pro is Veegum treated with amine to improve dispersability. Veegum Pro hydrates readily in hot or cold water to form high viscosity dispersions. Recommended for use where a minimum amount of water is required and/or only slow type mixers are available.
Other grades (like F, HV, K, R, HS) are used in non-ceramic applications (like pharmaceuticals and personal care products).
Since this is a mineral family it is very difficult to supply a chemistry. We recommend using the bentonite chemistry (it is possible in INSIGHT to label a recipe line as Veegum yet specify bentonite as the material database look-up value).
The whitest test bar here is a New-Zealand-kaolin-based cone 6 porcelain (employs VeeGum for plasticity). Immediately to the left of it are three North American-koalin-based bodies using standard bentonites. The bar to is right in a Grolleg based body that uses a standard bentonite rather than a white burning one. All are plastic.
The home-made kiln shelf (left) was fired it at cone 10. It is half the weight (and thickness) of the cordierite one (but remember that it does not have the thermal shock resistance of cordierite). It is made from a body consisting of 96.25% calcined alumina and 3.75% Veegum. It rolls out nicely and dries perfectly flat over about three days. But the Veegum does not give up its water easily. I cut it 1/4" larger than the other and it has fired to the same size; this body has incredibly low shrinkage.
It has taken a couple of days to reach this state, it still has a very high water content and needs another day or two of stiffening. This cracking occurs because much more water is needed to thin a slurry enough to be able to propeller mix it effectively. Typical clays can be dewatered in this manner in a few hours. By the way, this is fantastically plastic to use on the potters wheel, but this percentage of Veegum would not be affordable or practical.
Wow, just threw this mug from a porcelain having 10% Veegum plasticizer (of course no one could afford that, it is $15 a pound). But anyway, I was testing the extreme. These mugs did not twist during throwing, I could have pulled the wall thinner at the middle and top. The wall thickness at the bottom is 2.3mm (less than 3/32")! This mug is 15cm (6 in) tall. One problem: It takes forever to dry.
Each has been mixed with water and all produce a jelly-like translucent sticky material that takes a very very long time to dry. They are expensive and, among other uses, act as white-burning plasticizers in fine porcelain bodies.
This can happen during tooling (I am making a crucible here). While the plasticity is sufficient for throwing, at lower water contents it drops off quickly. This is a mix of 5% bentonite, 10% ball clay and 85% calcined alumina. For better trimming some refractory capability needs to be sacrificed for more ball clay (perhaps 20%).
When formulating a white throwing porcelain that employs a white expensive plasticizer (like Bentone or Veegum) the optimal range of percentages can be surprisingly narrow (I am assuming at least 40% kaolin is present). The trimming behavior is one indicator. When there is insufficient plasticizer the tool will chatter (of course in extreme cases edges will tear). Smoothing the corners after trimming (using your finger) will also give you an indication. If there is too much plasticizer, the material will ball up under your finger, if there is insufficient it will not smooth out well. The percentage can be critical: 0.5% too high and the drying shrinkage could sky rocket, 0.5% too low and lips can split at the rim during throwing.
This fine white New Zealand porcelain body has to be plasticized using an expensive white bentonite (VeeGum). In this test mix, the percentage of VeeGum was slightly low (3.25%). Although it is very plastic and throws well on the potters wheel, the tendency to split at the rim is evident on this dried mug. Only 0.5% more Veegum is needed to solve this issue. The percentage is critical, enough to eliminate this issue but not too much or the drying shrinkage will be excessive.
These two cone 10 porcelains have the same recipe. 50% Grolleg Kaolin and 25% each of silica and feldspar. But the one on the left is plasticized using 3.5% VeeGum T and the one on the right uses 5% regular raw bentonite. The VeeGum is obviously doing more than making it more workable, it is fluxing the body to make it much more translucent. Although not clear from this picture, the entire mug on the left is covered with blisters, it has over vitrified (while the one on the right is stable).
These two cone 10 porcelains have the same recipe (50:25:25 Grolleg kaolin, feldspar, silica). But the one on the left is plasticized using 3.5% VeeGum T while the one on the right has 5% raw bentonite. The VeeGum delivers better plasticity and obviously whiter color, but it is also acting as a very strong flux and has transformed the body into an over mature mass of blisters. That means it should be possible to make this porcelain using a 50:20:30 mix.
This is VeeGum T, a processed Hectorite clay (similar to bentonite, extremely small particle size). I have propeller-mixed enough powder into water that it has begun to gel. How long does it take for them to begin to settle? Never. This sat for a month with no visible change! That means it is colloidal.
Three cone 6 mugs. All have zero porosity. Why is the middle one so translucent? Three reasons. 1. It has 10% more feldspar than the one on the left and reaches zero porosity already at cone 5. 2. It employs New Zealand china clay while the one on the left contains high-TiO2 #6 Tile kaolin. But this is also true for the one on the right. The third difference is the key. 3. The center one contains 4% Veegum T plasticizer (while the other two use standard bentonite). This is surprising when I tell you one more thing: The mug on the right also contains 3% Ferro Frit 3110. That means that the frit does not have near the fluxing power of the VeeGum!
Veegum (left), Mineral Colloid and Gelwhite fired to cone 6 oxidation. The Veegum is dense and white, but not melting. The Mineral Colloid fires like a typical raw bentonite (dark brown, high soluble salts and beginning to melt). The Gelwhite is completely melted and foamed.
Out Bound Links
Montmorillonite, Bentonite USA
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In Bound Links
New Zealand Kaolin, New Zealand PFC
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