Clay Body Additives: Additive-A

May 12, 2010
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In the past 40 years, many clay additives or conditioners have been used in ceramic-related industries. Additive-A® is just one in a series of non-traditional methods of increasing the plastic properties of moist clay. In the past, potters used to “age” their moist clay in damp cellars or storage containers for years to achieve the effects that are now possible after a few minutes of clay mixing.

Additive-A is a blend of lignosulfonates and organic and inorganic chemicals that is produced by LignoTech USA. It is not-toxic, but normal handling precautions should be used when working with the material. When used in clay bodies, Additive-A increases the plastic characteristics of the clay without the need for additional ball clays or bentonite. Additive-A is a calcium lignosulfonate that has the ability to make water wetter, which means that less water is required to make a clay body more plastic. The less water used to achieve plasticity in any clay body, the lower the risk of clay body defects such as excessive shrinkage, warping and cracking during the first stages of firing.

The increase in plasticity is most noticeable in short or non-plastic clay bodies such as raku, sculpture, jigger and ram press formulas. Additive-A can also be used in soda, salt, low-fire and tile clay bodies. The plasticity of a clay body can be increased with additions of ball clays and/or bentonites. However, both types of clay need large amounts of water to make them plastic. Excessive amounts of ball clay can also make the body feel gummy and soft when moist, causing problems in the forming stages. The moist clay body can also exhibit thixotropy (a “jello”-like quality) when forms are pulled up on the wheel.

Benefits
Additive-A can replace all or part of the ball clay/bentonite component in clay body formulas. Additive-A in the clay body gives the potter greater flexibility to choose less-plastic clays in the clay body formula while also decreasing the amount of total water needed to make the clay body plastic.

The additive is a soluble, natural polymer that imparts a higher-charge density to the particle surface of the clay. It adsorbs onto the clay platelet, causing a negative charge that allows the clay platelets to slide past each other in the clay/water structure. In the clay mixing process, Additive-A acts as a lubricant in the clay mix, offering less resistance to pug mill and mixer parts. The decreased resistance in mixing lowers energy costs and extends the life of the clay mixer and pug mill. Lowering moist clay resistance and lubrication are critical factors in tile extrusion clay body formulas. Clay can be extruded faster and easier with Additive-A.

Additive-A softens the clay without the addition of extra water, which results in a denser, stronger clay body. It will also reduce the water of plasticity, which is the amount of water required to make the clay pliable. Using a smaller amount of water to achieve plasticity means there is less chance of shrinkage, warping, or cracking in the drying and firing stages. Additive-A also contains a lignin-derived binder that mechanically takes the place of some of the water in the clay body, causing adhesion of the clay plates.

Since it substantially increases the green and dry strength and dry strength of clay bodies, Additive-A makes for less fragile ware. Increasing the durability of unfired ware is crucial for large ceramic forms that require movement in the studio or loading into a kiln. Keep in mind that reprocessing dry clay scraps containing Additive-A requires a longer soaking time in water to break the clay down into a plastic mass because the dry clay is more dense.

Economic Considerations
All expenditures for ceramic materials must be looked at with the knowledge that labor is the largest cost to potters. Any additive to a clay body or glaze must reduce the handling cost or cut the defect rate. Apart from a few expensive raw materials (e.g., cobalt oxide, cobalt carbonate, tin oxide, synthetic red iron oxide, nickel oxide black, nickel oxide green, nickel carbonate, silver nitrate and stains), most materials that make up formulas are inexpensive. The most expensive factor is your labor and the time required to make pots or sculpture.

Clay body additives can range in price from $2.00/lb to $6.50/lb, depending on the additive and the amount needed to achieve the desired result. In clay body formulas, the additive component is usually 1/8% to 2% of the total formula weight. The price/lb of additive will typically increase the price of the clay by $.01 to $.02/lb, which is not a significant cost to the overall expense of the formula. The real savings occurs when the defect rate drops due to the use of the additive. If one pot or sculpture is saved because of using the additive, it more than pays for itself.

Using Additives
While the use of clay additives has increased significantly in the last few years, many potters often try to work around problems. They often develop difficult and time-consuming techniques, when just solving the problem would be a better long-term option. Often such "saving" measures are not reliable or are labor intensive. More time is typically spent trying to make do with an ineffective method that does not address the problem directly.

Set aside some time to find out exactly what kind clay body defect you are looking at and then see if a particular additive will work. Keep in mind that not all defects can be fixed by additives and other methods for a correction might need to be employed. An accurate diagnosis is essential for an exact correction. Fixing the problem once is better than struggling with a partial ineffective fix on a daily basis.

Don’t be intimidated by clay additives. If you are unsure about how and when to use an additive, contact the companies that produce them and ask for advice. Describe the problem in simple, direct terms. Your accurate description of what you are observing is a critical factor in the recommendation of an additive.

However, if you want to experiment on your own and are reasonably sure that an additive is an appropriate fix for the problem, start with the lowest possible amount of additive. If no change occurs, increasing the additive to the recommended amounts will often bring about the desired correction. It is always best to thoroughly test all additives in each formula. The major causes for failures are typically choosing an inappropriate additive for the situation, and using too much or too little of an additive.

The current generation of clay additives is potent, reliable and consistent. Clay additives cannot make bad pots better or sculpture more beautiful. However, they can give potters a tool to solve specific production problems.


Author’s Acknowledgments
I would like to thank LignoTech USA for providing information and technical help over the years. Their concern for accuracy and time spent to help me with information about Additive-A will always be greatly appreciated.

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