Drying Clay

Paper

(Allowing for Project Movement During Shrinkage)

Putting Paper Under Projects for the first several days of drying, helps absorb moisture from the bottom of projects, helps projects dry more uniformly, and allows the surface to move with the clay projects as they shrink (as opposed to putting them directly on a nonabsorbent, plastic or metal surface, such as a metal drying rack), thus reducing the chance of cracking.

Plastic

(Slowing the Drying, Evening Moisture Distribution, & Reducing Chance of Cracks)

Large Plastic Dry Cleaners Bags: Handbuilt pieces, especially those with many joins or attachments, should be dried slower than thrown pieces or pieces without attachments. Loosely draping plastic over sculptures can slow the drying and help prevent cracking as it allows for more even and uniform drying to the project as a whole. The plastic on top helps to create a sort of tent or slightly humid environment under which moisture can more evenly escape from the pieces. For instance, without plastic draped over, smaller pieces and attachments dry more quickly than the body of the piece and can crack.

Plastic Wrap: As smaller pieces of clay generally dry faster than larger pieces, draping or wrapping plastic wrap around small, delicate attachments and joins can help reduce cracking by slowing the drying of those parts while allowing other larger parts to dry at a faster pace, to ultimately help even out the drying.

Handles: Once formed, curve handles as desired and allow to setup (dry in the pose of the desired curve) to leather hard before attaching them to the vessels. If the handle is standing upright, as in this photo and needs support to hold its form, a dry sponge can be used. Special care should be taken (such as using plastic wrap) to keep moisture in the areas of the handle where it will attach to the body of the mug.

Wooden Ware Boards

If wire shelving is not available, sculptures can be placed on wooden ware boards to dry as the porous surface will allow moisture to escape. If desired, sculptures can be moved, after the first stage of drying, to a more dry spot of the board.

After throwing forms, be sure to immediately wire off the projects from the bat. Move the pieces to a wooden wareboard and allow the piece to firm up to the point where the rim is strong enough (soft end of leatherhard) to support the project when turned upside down. Once the rims are leatherhard, the pieces can then be turned upside down to allow the bottom of the pieces to reach leatherhard. When a thrown piece is leather hard, the foot can be trimmed. It is also a good idea to loosely cover the thrown forms in plastic to redistribute moisture and to slow the drying. The pieces should be checked daily to ensure that they do not dry too quickly before they have been trimmed.

Wire Shelving

Bisqueware Above, Greenware Below: If storing both bisque and unfired clay projects (greenware) on the same wire rack, it is best to store the bisqued projects on the top shelves with the unfired clay projects below so that any clay dust or residue does not fall onto the bisqued pieces.

Even Air Circulation: Placing clay projects on wire shelving (after the initial drying stages, otherwise a paper barrier should be used between the clay and wire shelving) allows for greater air circulation and, thus, more even drying to help prevent cracks.

Trimmed Pieces: Once trimmed, finished pieces should be moved to a metal drying rack, similar to this one (but without a bat or board underneath) so as to allow complete air circulation to the piece. (If the form has attachments, however, such as a mug, draping plastic over the form or around the attachment/join is a good idea to prevent cracking.)

In the Kiln (Kiln Off)

Loading Projects Before Bonedry: Pieces that are large or fragile can be loaded in the kiln during the later stages of leatherhard and allowed to dry completely to bone dry with the kiln off and lid left open.

Building on Kiln Shelf: Sometimes, when creating a very large delicate sculpture, it is advantageous to actually build the piece and to leave it on the kiln shelf during the entire drying process to eliminate further handling of a fragile piece.

Aluminum Silicate: Covering the kiln shelf with aluminum silicate powder can allow larger clay projects to more easily move or shift during the shrinking process to help prevent cracking.

Removing (the Majority of) Armatures

Once a piece is strong enough to support its own weight, the armature should (in most cases) be removed. Leaving a cardboard, metal, or plaster mold inside of a clay form while it dries can result in cracking as the clay form will shrink when as it dries.

While paper armatures can technically be left inside of a piece (provided that the paper is not so tightly packed that it allows room for the piece to shrink during the drying), especially in a school setting, it is advisable to have students remove larger pieces of paper from the inside of a sculpture to reduce smoke from entering the room. Small pieces of paper left inside of clay peices is okay. However, over time, removing paper armatures from pieces before firing can prolong the life of the elements in the kiln.

Troubleshooting Drying Problems

Repairing Cracked Sculpture with Scratching & Slip

Vinegar & Spit for Cracks: Sometimes, simply scratching and slipping is not sufficient to repair a crack or break. In those cases, after scratching both pieces, using vinegar or even spit (YES - a potter's secret!) in place of slip or as the base for a new slip-paste (ex. mixing vinegar with small dried pieces of clay), can sometimes do the trick!

Slowing the Drying of a Repaired Join: I also recommend that the area around the repaired join be slightly moistened. The repaired join and area moistened around the join should be wrapped in plastic wrap. This all helps to slow the drying of the join, reduce the shock to the sculpture of having only a small part being re-moistened for repair, and, thus, help reduce the chance of a re-break.

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