About Clay and How It Was Used by the Nelson McCoy Pottery

By Dewayne Imsand

We all know that the Nelson McCoy Sanitary Stoneware Company began in 1910, but did you know that the clay the pottery used at that time was laid down between 325 to 290 million years ago? This time period is called the Pennsylvanian and back then the climate and the Ohio landscape were very different than they are today. Back then much of the state and in fact the whole southeastern portion of the United States, was a low-lying area that was repeatedly inundated by ocean waters. Eroded soil and minerals from the highland rocks washed down and was deposited in the shallow water bottoms. Then, at intervals, many hundred of thousands of years later, the waters would recede and lush vegetation would cover the landscape. Gradually the climatic conditions would reverse and the waters would return killing the vegetation. As time progressed the eroded sediment would cover the decayed vegetation. Eventually the decayed vegetation would turn into coal and the eroded sediments would form a clay layer of various types, or form some rock-type formation. Determined from the number of coal beds found in the Zanesville region, there were over sixteen separate cycles of inundation and dry periods during the Pennsylvanian.

Due to the various amounts and types of soils and minerals that were eroded and deposited at each interval, all of the clay layers have some distinguishing characteristics. One of these clays known as Lower Kittanning, was found to be particularly useful in making stoneware. Kittanning is high-grade, buff or yellowish colored, plastic clay with few impurities. In the early days of the McCoy pottery, this is the clay that was used. Sometime around 1923 a mixture of 1/3 Kittanning clay and 2/3 Tionesta clay was used. Tionesta is another good, buff colored stoneware clay that lies at a greater depth and is older than the Kittanning. Both the Lower Kittanning and Tionesta would have been white clays, except that they contain a relative small amount of iron oxide.

As indicated by the original name of the McCoy pottery, the ware that the company first produced was stoneware. Stoneware is extremely strong and will not absorb water. It is fired at kiln temperatures ranging from 1200 ° C – 1300 ° C. A temperature in this range causes the clay to vitrify, i.e., it melts and fuses together and becomes glass-like, and is non-porous. Because stoneware is nonporous, it does not require a glaze to made it waterproof. However, when stoneware is glazed the glaze serves a purely decorative function. Initially the McCoy pottery used a salt glaze. This type glaze is applied while the ware is being fired in the kiln. Later a brown-colored slip glaze was also used, usually for the top one-half of croaks, jugs, churns, and similar items. These slip-type glazes normally require a second firing.

During the 1930’s the demand for utilitarian stoneware was in a decline. The Great Depression played a significant role in this decline. As time went on the public demand gradually changed from stoneware to colorful, decorative pieces. In response to the change in the demand, the pottery re-organized in 1933 and became known as the Nelson McCoy Pottery Co. Then in 1934, Sidney Cope was hired to assist Chief Designer Walter Bauer in designing the new wares. By 1936 Cope became the Chief Designer.

At first, various decorative designs were added to the sides of the same type symmetrical shapes that were formerly produced. The principle method used to produce these older pieces was by jiggering, which is a more efficient method than the hand method where a piece is formed by hand on a potter’s wheel. Curve-sided pieces, such as churns and jugs, were also produced by jiggering. These pieces are made in three operations. First, the bottom half of one of these pieces is jiggered, and in separate operation the top half is jiggered. Finally, the two pieces joined together and fired to form the completed piece.

In the jiggering process an appropriate amount of soft plastic clay is placed inside a rotating plaster mold that forms the outside shape of the piece, say a jardiniere. Then an arm that has been formed into the desired size and shape of the inside of the jardiniere is lowered into the mold to the proper depth to force the clay against bottom and sides. The excess clay that extrudes above the top of the mold is cut off and the mold is removed from the wheel and allowed to dry. When enough drying has occurred the clay shrinks to the point where the ware can be safely removed from the mold.

The jiggering process had been invented in 1870, and it was still the production technique of choice when the Nelson McCoy pottery was established in1910. Jiggered stoneware at the pottery reigned supreme for nearly three decades, however the further decrease in demand for stoneware in the late 1930’s marked the time of change. One change was that the pottery began earthenware production. This ceramic type gradually replaced stoneware and it was the type ware that was produced throughout the remaining life of the pottery.

Earthenware is also made from fired clay, but it is fired at a lower temperature than stoneware, and it is porous and readily absorbs water. Typically, earthenware is glazed and fired a second time. During this second firing the fine glaze particles covering the surface fuse into a glass-like layer, sealing the pores of the clay body. Another benefit of this second firing is decorative in nature. It allows the various pieces to be produced in all types of glaze colors.

The most significant production change made during the 1940’s was made because the new more complex designs wanted by the public could not be produced by jiggering; they had to be cast. In the casting production method a dense slip, i.e. a clay slurry, is poured into usually two or three piece plaster mold. The absorbent plaster pulls water from the slurry and over a short period of time a clay layer builds up against the inside surface of the mold. When the desired thickness is reached the remaining slurry is poured out. The mold is allowed to dry for a brief time and as it does, the stiffened clay inside shrinks slightly. The mold is then separated and the item removed.

Although casting was a brand new production technique for the pottery, and a necessary one, it did not totally replace the jiggering method. But then in the mid-1940s another innovation, the ram press was invented. It was another valuable addition to the pottery for certain simple-shaped pieces after 1950. In the ram press process, a two-piece, hard plaster mold is used. One-half of the mold of some simple shape, such as a bowl or plate, is placed on the bed of the press and the other half on the ram, which is positioned directly above the bed mold. An appropriate amount of plastic clay is placed on the base mold and the ram is activated. It lowers onto the base mold and as the two mold halves meet, the clay is pressed against the two molds under high pressure. Excess clay extrudes from the sides of the mold and the desired shape is produced. Along with jiggering, the ram press and the casting process were used through the life of the pottery.

The local Lower Kittanning and Tionesta clays were used by the pottery for years and produced suitable wares through both the jiggering and the ram press processes. Both are high-grade plastic clays, however for making castings and glazing slips there is better type clay and it is one that has the most desirable characteristic for these purposes. The best clay for casting and glaze slips is one that has the ability to thoroughly mix with water. The premiere clay for these uses is called Ball clay.

Ball clay is an extremely rare mineral found in very few places around the world. The particles making up this clay have the smallest size of any clay, and the clay is the most plastic, the most sticky, and has a high rate of shrinkage upon drying. The small particle size produces excellent clay slurries. Kaolinite is the predominate clay mineral in Ball clay and as a result of this, and the lack of impurities, the clay has a white color after firing.

Although casting was known to potters in American since before the Civil War, the need for the Nelson McCoy pottery to adopt this technique was not necessary until the decision was made in the 1930’s to go into “art pottery” production. It is believed that the use of the white-burning Ball clay by the pottery for glazes predates the full-scale use of it for casting. The plan to produce highly decorative pieces by casting was most probably stymied by political events, which dictated it would be a slow start. Because of the lack of pottery demand and rationing brought on by World War II, from 1941 to 1945, the McCoy pottery only produced about 10 percent of the number of (non-military) items that were produced immediately before the war. A large military contract to produce landmine casings was of great benefit to the pottery during this bleak time.

Following the war the demand for pottery slowly increased and the number of different pieces produced by the pottery also increased. Many new designs were added to the inventory each year and probably a few of these pieces were cast. However, casting had not come to the forefront yet and jiggering was still the major production technique. Even the production of many of the large jiggered stoneware pieces was continued after the war, until about 1950.

The year 1950 was a real turning point in the history of the pottery. A fire that year destroyed the entire manufacturing portion of the pottery. It was decided that rather than just rebuild, the pottery would begin anew with all new and modern equipment. It is believed that the casting process was emphasized in the modernization.

Following the fire, some production resumed at the pottery after about six months, but full production was not achieved until about 18 months had passed. Luckily, the pottery modernization was just in time to take advantage of the 1950’s boom in pottery demand. It is believed that this was the time that the casting process began in full force. In keeping with the plan to have a state-of-the-art pottery plant and the need to convert to casting as a major production process, along with the demise of stoneware, it is likely that the use of Ball clay now became the principle clay used by the pottery.

Since Ball clay is not available in the Zanesville region, it had to be acquired from outside sources. The McCoy pottery first arranged to acquire the clay from the Cooley Clay Co. located in Kentucky. The larger, Old Hickory Clay Co. of Hickory, Kentucky later acquired this company. Old Hickory was founded in1918 and has several large mines in western Kentucky and western Tennessee. The mine that supplied Ball clay to the McCoy pottery is located in Gleason, Tennessee. The white, Kaolinite clay from this mine was used until the pottery closed in 1990.