Clay Body Additives


In the past forty 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 in a few minutes of clay mixing. Additive A was developed in the1950's to meet the country's needs of increased brick production for housing. At that time brick production throughout the United States was antiquated. Most bricks were fired in periodic kilns that we slow and labor intensive. Due to the increased demand for building bricks many plants automated their production processing and handling equipment for faster production. Today high-speed mechanized processes make bricks. Labor and production costs went down due to mechanization. However, brick loss rates increased due to the wet unfired bricks being formed and moved around the plant by machines. Many bricks were cracked or damaged by the high-speed machines. Due to high loss rates and the relative non-plastic characteristics of brick clays and low grade shale’s there was a need for a modifier to increase the green strength and plasticity of the bricks.

During this time of mechanization and expansion lignosulphates (a by product of wood for paper production) was shown to increase the bonding and forming characteristics of moist clay. Archibald R. Gmeiner and Carlton H. Hougue were the two people most responsible for developing and testing this type of new additive.1 Soon variations of the original additive were tested to meet the needs of local deposits of brick clay found at production plants around the country.

In 1972 research into clay body additives was conducted at Alfred University, College of Ceramics, Alfred, NY. Additive A was extensively tested and proved successful in wheel thrown functional pottery clay body formulas and large scale ceramic sculptures clay bodies. It was found that clay body color and maturing temperature were not changed as the additive is burned off before dull red heat (approx. 1000 0 f. to 1100 0 f.) is reached in the kiln.  

Additive A is a blend of lignosulphonates, organic and inorganic chemicals produced by Lignotech USA.2  It is not-toxic but normal handling precautions should be used working with the material. It is used as an addition to brick making clays and other industrial ceramic products. 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 ligno sulphonate, which has the ability to make water wetter, causing less water to be used to make a clay body more plastic. The less water used to achieve plasticity in any clay body reduces 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 or a “jello” like quality when forms are pulled up on the wheel. 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.

Many ceramic suppliers such as, Ceramic Supply of NY/NJ, 7 Route 46 West, Lodi, NJ 07644 ph 1 973 340 3005 are now using Additive A in their new series of moist HMI clay body formulas. Larry Sussberg, owner of the company states, “while the additive does add extra cost to the clay bodies it dramatically increases the handling properties of the product we sell to potters. I am very satisfied with this additive as it sets us apart from the competition in a very competitive market.”

Active lubricant in the clay mixing and forming stages
Additive A is a soluble, natural polymer, which imparts a higher charge density to the particle surface of the clay. It absorbs onto the clay platelet causing a negative charge which 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 which offers 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 will be extruded faster and easier with Additive A.  

Increases clay body dry and green strength
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.3 With less water used to achieve plasticity there is less chance of shrinkage, warping, or cracking in the drying and firing stages. It 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. Additive A substantially increases the green strength (pots that have been formed and are still not dry) and dry strength (pots that have been formed and are already dry) of clay bodies making for less fragile ware. It will reduce chipping and damage caused by handling the ware. Increasing the durability of unfired ware is crucial for large ceramic forms that require movement in the studio or loading into a kiln. 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.

Types of Additive A
Additive A can be purchased in liquid or dry powder form. Several ratios of Additive A to barium carbonate mixtures can be purchased. Type 1 contains 2-4 lbs. per/2000 lbs. equivalent of barium carbonate, Type 3 contains 5-7 lbs. per/2000 lbs. equivalent of barium carbonate, Type 4 contains 8-10 lbs. equivalent of barium carbonate, (Type 1, 3, and 4 are only sold in liquid form) and Type 2 does not contain any barium carbonate.

Additive A - Type 1, 3, and 4 contain barium that is chemically linked in the polymeric structure of the lignosulphonate. Because of this chemical linkage, the hazards of dry barium powder are largely eliminated. Type 3 reacts with the soluble sulfates in the raw materials and changes into an insoluble barium sulfate. After firing the ware will be clear burned.

Calcium sulfate and magnesium sulfate can travel to the clay body surface upon drying causing an insoluble white residue, which appears as a white "fuzzy" material on the dried clay body. Types 1, 3, and 4, can be used in any clay body including low fire red clay bodies to neutralize soluble salt scrumming. In fired ware the soluble salt scumming appears as a white flake material that can occur after the firing or days or months after the clay is exposed to any moisture. The best example of soluble salts in clay bodies is to observe red building bricks after it rains and notice the white residue on their surface. Besides Additive A contributing plasticity and green strength to clay bodies, the safe application of barium to stop scumming is a considerable inducement to use this additive.

Mixing Additive A
The most effective method of mixing the additive is to start adding water to the dry clay mix until the moist clay starts to ball up, then Additive A can be added to the mixture. Additional water is added to get the desired moisture content for the forming operation. Additive A can also be mixed in hot water and thoroughly dispersed, then all of the water/Additive A mixture is used in the clay mixing operation. Complete and through mixing of the additive in the clay mixture is critical in any mixing operation.  

Every gallon of the liquid form of Additive A contains 5.3 lbs. water and 5.3 lbs. of Additive A. When using the liquid form always base the amount of additive on the dry component weight of the liquid. Additive A can be used in clay bodies from 0.25% to 2% based on the dry weight of the clay body formula. In most throwing and handbuilding clay body formulas often 1/16% to 1/8% will significantly improve the handling qualities of the clay.  Additions of Additive A to the clay body of more than 5% will greatly increase green and dry strength causing the clay to become extremely hard when dry. In some instances the dry clay can be dropped on the floor without breaking. Start by using 0.25% then increase the amount of Additive A by 0.25% increments until the desired results are achieved.

Economic benefits from Clay Body and Glaze Additives
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 handling cost or cut the defect rate. Apart from a few highly expensive raw materials, such as 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 time required to make pots or sculpture.

Clay body additives can range in price from $ 2.00 per/lb. to $ 6.50 per/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. In most clay body formulas the price per/lb. of additive will increase the price of the clay by .01 to .02-cent's per/lb., which is not a significant cost to the overall expense of the formula. The real saving 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.

While the use of clay additives has increased greatly 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. Typically more time is spent trying to make do with an ineffective method that does not address the problem directly. Such procedures often use time and labor that are valuable. Solving the problem is always better and less expensive. 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 not all defects can be fixed by additives and other methods for a correction should 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 on how and when to use an additive contact the companies that produce the additives 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 amount of additive. If no change occurs often increasing the additive to the recommended amounts will bring about a correction to the problem. As with all additives, it is always best to thoroughly test them in each formula. When they do not work the major causes for failures are, 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 the potter a tool to solve specific production problems.  
1. "Additive A. . . . from whence it came"  by, Carlton H. Hougue
2. Borregaard Corporation, This email address is being protected from spambots. You need JavaScript enabled to view it.  ph 940 781 1715
3. Water of plasticity is the amount of water required to surround each clay platelet with a film of water to achieve a plastic mass of clay.

I would like to thank Scott McBride, of Lignotech USA for his information and technical help over the years. His concern for accuracy and the time he spent in helping me with information about Additive A will always be greatly appreciated.

Jeff Zamek received BFA/MFA degrees in ceramics from Alfred University, College of Ceramics in New York. In 1980 he started his own ceramics consulting firm and has contributed articles to Ceramics Monthly, Pottery Making Illustrated, Clay Times, Studio Potter and Craft Horizons. This article is based on information from his book, What Every Potter Should Know, available for $ 31.50 from Jeff Zamek/Ceramics Consulting Services, 6 Glendale Woods Dr., Southampton, MA 01073 ph 413 527 7337.