Colorware History & Design

The Maximalist

Pacific Pottery Manufacturing

Pottery production saw rapid innovation in the 1920s and 30s. Pacific Pottery manufacturing processes were highly efficient and automated – even through the depression, the company continued to invest in technologies to make their plants more productive, giving them the ability to increase production while keeping labor costs low. However, even with all the automation, humans touched every single piece of pottery that was produced (even in modern day facilities like Homer Laughlin, you might be surprised how much handwork goes into the creation the pottery). Today, machines have taken the place of hand pressing, jiggering and jollying for most production, although slipcasting processes are fairly similar.

The firing process

The pottery is shaped from clay using a variety of techniques:

  • Hand pressing: Using a hand jigger, clay can be fitted into a mold and then pressed to create an embossed decoration.
  • Jiggering and jollying: Starting with a lump of clay, a pottery would use a rotary jigger: a machine with a spinning wheel and that forms the outside of a plate or bowl, for example, and a jolly to form the inside. As the plate spins, the piece is formed and excess clay removed.
  • Slipcasting: Slipcasting is a technique used in pottery manufacturing where liquid clay is poured into a plaster mold, forming a cast on the inside of the mold. Items like cup handles, for example, are typically created in a solid-cast mold. Liquid slip is used to bind the handle to the body. Slipcasting is also used to produce hollowware pieces (carafes, pitchers, teapots, etc.). Often, the piece was created in two separate halves, and then joined and smoothed by hand. This is why you’ll often see a seam on these types of pottery. Production costs for these pieces would be high due to the handwork involved.
Pacific Clay Products - jigger operator

Pacific Clay Products – jigger operator

At this stage the greenware pieces are set out to dry. Before the first firing, as much water as possible should be removed from the greenware to ensure even firing and avoid cracking and separation. Once the pottery is dry, it goes through its first firing, or bisque firing. Bisque firing changes clay into ceramic material. Depending on the clay, there can be a lot of shrinkage during the firing process. When I toured the Homer Laughlin China Company factory, they told me that their clay shrinks around 7-10%. So the molds used to create the pieces are quite a bit bigger than the finished product. Some California potteries, such as Bauer Pottery sold their bisqueware items to other distributors and consumers. Many local artists painted on the bisque and resold the items in their own small shops.

Pacific Clay Products factory floor

Pacific Clay Products Plant #4 factory floor – note the molds for the #420 ball pitcher and #440 teapot (employee Fred Wind, Jr. on left)

Decorations

But for most potteries, bisque firing was just the first phase of the production process. Depending on the pottery line or pattern, the item was then decorated or color-glazed. Decorated items could be under-, in/on- or overglazed.

  • Underglazed: This is the process of applying the decoration to the bisque pottery before glazing. The decoration could be in the form of a decal or stencil, or hand painted-on designs. Underglazed decorations are extremely durable. Once the decoration is applied, the item is glazed and refired. This technique comes into vogue in 1940s dinnerware.
  • In- or On-glazed: In- and on-glazing decorating processes are two methods of applying the decoration. The materials used in these processes fuse to the glaze, making the decoration more durable. Pacific Pottery used in-glazing on their decorated-ware.
  • Overglazed: These are decorations, primarily decals, which are applied to the pottery after the final glazing process. In the 1920s and 30s, many third-party retailers would buy blanks from pottery manufacturers and apply their own decorations and brand name. Overglazed decals typically do not wear well as they tend to scuff over time. Many Ohio Valley potteries used overglazing techniques.

Glazes

Ceramic glazes are comprised of three primary elements. A glaze is a form of glass (silicon dioxide or silica) that is been modified to bond with clay. Since glass has such a high melting point, additional elements are added to lower the melting temperature. Fluxes are a melting agent added to silica to lower the melting point: Low fire glazes require more melting, and as a result, more flux is included. The third ingredient, alumina, helps the glaze shrink to fit the clay body.

A base glaze is comprised of different amounts of silica, flux and alumina. The base glaze is white or clear in color. Glazes get their colors from colorants (metal oxides) added to the base glaze. The combination of the three elements in the base glaze also determines the appropriate melting temperature, surface sheen, colorant response and glaze fit.

Due to shrinkage of both the clay and glaze during the firing process, clays and glazes need to be appropriately matched. If the glaze contracts more than the clay, you get crazing. If the reverse happens, you get peeling. Sometimes crazing is intentional as a design element. However, both crazing and peeling are not desirable effects for dinnerware.

Check out the Colorware page for more information on 1930s glaze colors.

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