Calcium lignosulfonate* is just one in a series of non-traditional methods of increasing the plastic properties of clay. Developed in 1950s to increase the plasticity and green strength of brick,1 calcium lignosulfonate is now used in almost every type of ceramic manufacturing operation. When used in clay bodies, calcium lignosulfonate makes the water “wetter,” allowing less water to be used to make the clay body more plastic. The additive contains a lignin-derived binder that mechanically takes the place of some water in the clay body, causing adhesion of the clay plates. This action reduces the risk of clay body defects, such as excessive shrinkage, warping and cracking during drying and firing.
The increase in plasticity is most noticeable in short or non-plastic clay bodies, such as Raku, sculpture, and jigger- and ram-pressed formulas. The additive can also be used in soda, salt, porcelain, low-fire and tile clay bodies.
Traditionally, ball clays and/or bentonites have been used to increase plasticity, but both types of clay need large amounts of water to make them plastic. Additionally, excessive amounts of ball clay can make the body feel gummy and soft when moist, causing problems in the forming stages. The moist clay body can also exhibit thixotropy or a “jello-like” quality when forms are pulled up on a pottery wheel. Calcium lignosulfonate can replace all or part of the ball clay/bentonite component in clay body formulas, giving potters greater flexibility to choose non-plastic clays in their formulas while also decreasing the total amount of water required.
Calcium lignosulfonate also substantially increases the green strength (e.g., pots that are formed but are not dry) and dry strength (e.g., pots that have been formed and dried) of clay bodies, reducing chipping and damage caused by handling the ware. Increasing the durability of unfired ware is especially crucial for large ceramic forms that must be moved around in the studio or loaded onto a kiln.
Because they contain barium carbonate, Types 1, 3 and 4 are only available in a liquid form that chemically links the barium to the polymeric structure of the lignosulfonate. This chemical linkage eliminates the hazards that are associated with dry barium powder. (Barium carbonate is toxic if ingested.)
All types of calcium lignosulfonate can be safely used in any clay body, including low-fire red clay bodies. While none of the different types of calcium lignosulfonate are toxic, normal handling precautions should be used when working with any form of the additive.
Every gallon of the liquid form of calcium lignosulfonate contains 5.3 lbs of water and 5.3 lbs of the additive. When using the liquid form, always base the amount of additive used on the dry component weight of the liquid. The additive can be used in clay bodies from 0.25 to 2% of the total dry weight of the clay body formula. In most throwing and handbuilding clay body formulas, an even lower amount can be used—as little as 1⁄16 to 1⁄8% will significantly improve the handling qualities of the clay. Additions of more than 5% will greatly increase green and dry strength, causing the clay to become extremely hard when dry—in some cases, the clay can even be dropped on the floor without breaking. Start by using 0.25%, then increase the amount of additive in 0.25% increments until the desired results are achieved.
Some ceramic suppliers have also begun using calcium lignosulfonate in their clay body formulas, making it even easier for potters to gain the benefits of the additive without having to worry about mix ratios. Ceramic Supply in Lodi, N.J., is just one such company that recently began using the additive in its moist HMI clay body formulas to increase customer satisfaction. “While the additive does add extra cost to the clay bodies, it dramatically increases the handling properties of the product,” said Larry Sussberg, the company’s owner.
While the extra expense may cause some potters to shy away from using additives, the costs can often be easily recovered through fewer defects and less waste if the right additives are used. One pot or sculpture saved through using an additive can be enough for the additive to pay for itself.
If you want to experiment on your own and are reasonably sure that an additive is the appropriate fix for the problem, start with the lowest amount possible. If no change occurs, try increasing the amount of additive in small increments until you achieve the results you are looking for. If the additive does not produce the anticipated results, you may be using an incorrect amount or the wrong additive for your formula, and more testing may be required.
Today’s potters can choose from a variety of additives that are potent, reliable and consistent. Clay additives cannot make bad pots better or sculpture more beautiful, but they can give the potter a tool to solve specific production problems.