"When reproducing a new Julia Morgan pattern for his line...Kellenbeck begins by pressing clay into the original mold, then frames around the imprint and casts it in plaster. That creates the face plate with which the model is built.

The model is the top of the working die. A face plate must be cast first because the face plate surface is the negative of the tile.

When building a model, Kellenbeck recesses the face plate into the pressing platform. Quarter-round wood molding is used to define the cutoff edge, which is half the thickness of the tile to be pressed. He then frames up a box around the model, making sure the block and case that will be cast from this will be large enough to set a die ring on.

"Mold soap" made from a 50:50 mixture of lecithin and vegetable oil is used on the plaster face plate. "Forgetting this separator means starting over from scratch," noted Kellenbeck.

The working (RAM-process) die is cast next: Chicken wire is secured in the die ring, and mold duct-canvas tubing with air fittings-is loosely woven through the chicken wire. It must be suspended 2 to 3 inches above the face of the block and case. About 2 inches should separate the mold duct coils; too much tubing will blow the casting.

Before placing the ring on the block, it is imperative to coat the entire block with mold soap. The edges of the ring are then sealed with wet clay and the whole assemblage placed on a vibrating table to cast the plaster (Kellenbeck uses Hydrostone).

Now comes the part that requires experience gained from lots of practice. Compressed air introduced very slowly into the setting plaster will force the water out, leaving behind a porous mold that will later allow quick release of wet clay tiles after pressing. Kellenbeck waits for the water slick to disappear from the top of the plaster, then begins putting a small amount of air throughl the mold duct, starting with about 3 pounds (psi) of pressure.

As the plaster continues to set up, he gently increases the amount of air pressure by about 2 pounds each minute. Differences in temperature require seatof-the-pants adjustments.

Water will begin forcing its way to the top of the casting at about 18 to 2O pounds pressure. If Kellenbeck doesn't see any water, he knows the air was introduced tOO slowly; but pressure increased too quickly will blow the mold.

Once this water purge has begun, pressure can be increased approximately 5 pounds at a time, up to a maximum of about 75 pounds over a period of 15 to 2O minutes. These are general directions, Kellenbeck cautioned. Like throwing a pot, purging a mold is done mainly by feel.

At about 30 pounds of pressure, the mold will float itself out of the block and case, and water will foam up around the edge of the ring. When there is a good bubble pattern around the edge, the die can be lifted out of the block and case. and set on boards over a trash can to complete the purging process. However, moving the die too soon can mean damaging its face.

As the mold foams, bubbles can he removed with a sponge. At maximum pressure, very little water will surface. The die is then set aside to cure for 24 hours before being used on the press. "The key to designing presses and using the die mold process is keeping all parallel lines "true," Kellenbeck explained. In otherwords: die rings, pressing platforms, the face of the block and case must align well.

Kellenbeck's manually operated press generates 8000 ponds of pressure through gearing, not expensive hydraulics. The tiles are pressed from a commercial clay body that matures at Cone 06-02.