What are Additives for Ceramic Glazes? How do the Additives improve the Pottery materials? Do the Additives impact the precipitation? Do the Additives make the Glazes more liquid
Additives for Ceramic Glazes and Pottery
Substances Added to Glazes to Enhance Physical Handling Qualities and Typically Burn Off During Firing
In industrial settings, all glazes, decorative inks, and engobes contain additives. These are considered vital for managing properties such as cohesion, adhesion, suspension, dry surface strength, smooth leveling, flow behavior (rheology), drying speed, and more. In contrast, among studio potters and hobbyists, it’s fairly common for glazes to contain no additives at all.
Enhancing Ordinary Glazes with Additives
Use Agents Like CMC Gum to Improve Glaze Performance
Sometimes, a glaze may work well for a specific application but fall short in another. For example, a glaze might be ideal for dipping or pouring, yet dry too quickly during brushing, making it difficult to apply an even layer. Glaze additives act as key enhancers to address such limitations.
There are a number of additives that help optimize glaze behavior depending on the method of application—whether brushing, dipping, or pouring. These additives are generally classified as binders and suspending agents. According to ceramic artist Dave Pier, who has extensive experience with glaze additives and even formulated his own, most additives offer a combination of both functions—improving suspension and strengthening the bond between the bisque ware and unfired glaze.
Additives for Brush Application
Additives like Bentonite and Veegum-T are less effective for brushing, as they do not significantly alter the drying speed. Brushing with these still causes drag and uneven coverage. However, additives such as CMC Gum, Apt-II, Spectrum Brushing Medium, and Magma noticeably improve how glazes behave when brushed on. They extend the drying time, enabling more flexibility and movement before the glaze absorbs into the bisque surface. They also lower surface tension, allowing the glaze to flow more easily instead of clumping.
Once the first layer has dried, a second coat can be applied without disturbing the underlying one.
Tip: If you're out of the above additives, a small amount of liquid dish soap can help. It reduces surface tension, improving flow during brushing. This won’t affect the glaze’s durability when dry. When applying colored glazes over an unfired base glaze, additives like CMC Gum, Apt-II, Spectrum Brushing Media, and Spectrum Glaze Thinner proved useful due to their slower drying rate and smoother application.
Additives for Dipping and Pouring
For techniques such as dipping or pouring, Bentonite and Veegum-T perform effectively, as do Spectrum’s Glaze Thinner and Suspension Agent. These additives minimize the need for constant stirring and help the glaze adhere better to test tiles. CMC Gum, Apt-II, Spectrum Brushing Media, and Magma also allowed for thicker glaze application during dipping. Glazes mixed with Magma could be layered into very thick coatings without cracking or flaking.
These additives are especially useful in decorative methods involving carving through the glaze, as they enhance the hardness of the raw coating. This results in cleaner, sharper carved lines.
Additives for Reapplying Glaze
When re-glazing already fired pieces, Magma, CMC gum, and Spectrum Brushing Media were beneficial, even when used at room temperature. However, due to their slower drying nature, the process took longer and glaze layers remained relatively thin. When the ceramic pieces were pre-heated, glaze built up more efficiently and the results were superior compared to re-glazing without any additives.
Apt-II stood out as the only product that could produce a thick, single-coat glaze layer on previously fired ware without the need for preheating. As an acrylic-based medium, it behaves differently from the others, which are derived from natural gums.
