| Description |
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 flakey 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.
It is important to properly hydrate the powder, mix it in water before adding other ingredients (different grades of Veegum hydrate at different rates). The manufacturer emphasizes 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).
In bodies VGT is employed as a plasticizing agent. For example, in completely nonplastic formulations such as high alumina or zirconia bodies, VGT alone can produce sufficient working plastic. White burning porcelains are non-plastic by nature, but VGT is sufficient amounts (up to 5%) can produce a very plastic and workable material. It is a nonmigrating binder because it is not dissolved in the water. The material is clean and therefore does not affect fired whiteness.
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. |