Slipped, Jiggered, Slabbed and Extruded

Slip is a slurry of liquid clay that is used to create forms by pouring the liquid into plaster master molds. The plaster slowly leaches out the moisture from the liquid, forming a shell within the mold. At a desired thickness, the excess slip is poured back into the vat and the slip cast item is allowed to dry in the mold to the leather-hard stage. It is then lifted out of the mold and trimmed. It is at this stage that handles or other added features are attached. The item is allowed to dry and any final surface treatment such as sanding or smoothing of seams or joins is done.

Clays that lend themselves to slip casting are those with a fine consistency like porcelain or earthenware without heavy grog. Smoothness of the slurry is vital to insure a smooth surface and ease of trim and attachment.

Slips can be purchased for large-scale pouring or created by hydrating clean, dry scrap with water and allowing the mixture to ripen for a few hours. The smoothness needed for attachment of handles and other parts is achieved by stirring the wet, soupy clay to remove any residual lumps. Bamboo brushes make the application of slip easy, as they charge with high amounts of slip and release the slurry readily. Slip is also an excellent surface decoration for finished, trimmed leather-hard pots. Subtle to dramatic, the texture you use will show through the glaze. Dots, slashes, and zigzag lines all look dramatic and can be applied with a slip trailer bulb or bottle system or a children's ear syringe.

Jiggering machines are very useful for potters and ceramicists who deal in large volumes of repeated forms. What is a jigger? It is a machine that spins the clay. The clay is placed inside a mold shape that conforms to the outside of the shape being duplicated. A profile tool is attached to the jigger arm and is pulled down into the spinning clay. The profile tool is made to conform to the inside shape of the pot so that as it is pulled into the clay, it both pushes the clay against the mold and at the same time it cuts out the inside form. This action is similar to a potter's hands applying pressure to both sides of the wall of clay, and in mere seconds a pot is completed.

The mold and the resulting clay form are removed from the jigger and placed on a ware rack to dry. Then another lump of clay is placed in the jigger and the process is repeated. Speed, accuracy and exact duplication are the end result. The clay shape pops out of the mold a short time later and is gently scraped with a trimming tool to remove any mold marks and the trimming area is lightly sponged.

Slab rollers are a long-standing item in pottery studios. They can be of assistance to the potter whether or not he/she exclusively creates hand built pottery items. The process of creating rolled slabs is simple. Wedged clay is placed between strips of canvas and is pulled between rollers set at a specific depth or under a single roller set to a desired thickness. Sometimes it is the clay (on a base mat) that moves and sometimes it is the roller system that moves over the clay; but either way, the result is a smooth, evenly pressed strip of clay. Duplication of thickness and uniform lengths of varying widths are easy to achieve. This is a far cry from what is possible for most potters using a wooden dowel or a rolling pin.

Clay extruders are fairly simple in operation, and they consist primarily of a large tube of metal that is filled with clay. A tamper arm is thrust against the clay and pushes out a clay shape at the bottom of the metal tube. It is very similar to a large cookie press. Extruders are most valuable in the formation of hollow ware like goblet stems, tubular teapot handles and the like and are also indispensable for making yards and yards of clay ribbons from which handles can be fashioned. Discs (dies) can be created (from clay, plastic, wood or metal) to duplicate shapes of all kinds. Hollow tubes in varying sizes and shapes can be created with dies, available from most manufacturers.

Combination forms using two or more of these methods can be very interesting to create. Rather than rely on one method, using several techniques to create your work gives interest and could save you lots of time. Consider the value of a clay extruder...rather than creating tube shapes with slabs that have seams. Or consider the quality of a slip cast service plate with side handles that are extruded or hand built. Nothing could be more natural and lovely. Using a combination of techniques gives you the opportunity to do some over-the-edge designing, too. As an example, instead of extruded side handles on a plate, why not put a grip handle right in the middle of the plate? You could serve easily with one hand and have a neat conversation piece at the same time. And who says mugs must be slip cast (or thrown)? Hand built works with added decorations of clay strips, balls, flattened shapes and slip trailing are wonderfully original.

You may wish to take a class at a local art center/store or continuing education site and try slip cast creation and decoration or perhaps hand building or jiggering.