Digitalfire Ceramic Materials Database
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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 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; often a lot more water is needed to produced the desired viscosity. 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 more of the material (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, so 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 (it is clean and therefore does not affect fired whiteness). 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 sufficient amounts (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 other materials. 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.
VGT has a high pH of 8.5 and yet acts as a flocculant, contributing to the workability of porcelain. 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.
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. To the right of it is a Grolleg-based body at cone 11. 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.
This 10% Veegum porcelain was slurried and then poured on to a plaster bat to dewater. 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.
Ridiculously plastic! 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.
Wet, just-formed buttons of Mineral Colloid BP, Gelwhite H and Veegum T. 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.
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.
When bodies contain excessive non-plastics and are plasticized using high amounts of bentonite, this can happen during tooling (I am making a crucible). 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%).
Out Bound Links
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In Bound Links
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