What Happens To Air Dry Clay If You Bake It?

Table of Contents

What is Air Dry Clay?

Air dry clay is a modeling material made primarily from clay and a non-toxic, water-soluble polymer. It is lightweight, easy to work with, and air dries naturally to a durable, solid material at room temperature. The main ingredients in air dry clay are:

Clay – Provides structure and plasticity
Polymer – Acts as a binder to harden the clay
Water – Allows the clay to be molded
Preservatives – Prevent mold and bacterial growth

There are two main types of air dry clay: regular air dry clay that dries at room temperature and quick-dry formula clay that dries faster with low-heat baking. Both produce a solid, permanent material when fully cured that can be decorated and used for various crafts and projects.

What Happens During Air Drying?

When left to dry in open air, air dry clay hardens as the water it contains evaporates. Typically, air dry clay achieves a workable leather-hard consistency in 1-3 hours. At this stage, the clay is firm enough to hold its shape, but still pliable enough to sculpt details. After 12-24 hours of air drying, most air dry clays will be completely hardened and ready for baking.

The texture of air dried clay depends on several factors, including the clay composition, drying conditions, and thickness of the clay. Thinner pieces will dry faster than thicker ones. Air drying produces a more porous surface than baking, so air dried pieces will feel a bit rough or grainy to the touch. Properly dried clay is quite durable, but can still chip or crack if subjected to sharp impacts or blows.

Preparing Air Dry Clay for Baking

Before baking air dry clay, it’s important that the pieces are fully dried and hardened. Air dry clay is pliable and moldable in its initial form, but needs to cure and harden completely through evaporation before being baked. When air dry clay is first formed, it feels soft and almost wet. As it sits exposed to air, the moisture evaporates from the clay which causes it to harden and become less malleable over 12-24 hours. The timing can vary based on climate conditions, thickness of the clay pieces, and the specific clay brand.

It’s best to allow air dry clay pieces to fully cure and harden for 24-48 hours before baking. The pieces should be completely dry to the touch with no remaining tackiness or moisture. Fully cured pieces will feel firm and solid. Any moisture left in the clay will evaporate rapidly in the oven, potentially cracking or warping pieces. The clay may also not reach the proper hardness if baked before fully dried.

Air dry clay pieces should be clean and free of any dust or debris before being placed in the oven. The pieces can be gently brushed off if needed. Make sure the air dry clay pieces are arranged with sufficient space on the baking sheet or dish to allow proper heat circulation during baking.

Baking Temperatures and Times

When baking air dry clay, it’s important to use the proper temperature range. Air dry clay generally needs to be baked between 225-275°F. Lower temperatures may not fully cure the clay, while temperatures above 300°F can scorch the clay.

Recommended baking times will vary based on the thickness and size of your clay pieces, as well as your oven and clay brand. Most standard air dry clay items require 15-30 minutes of baking at 250°F. For a 1/4 inch piece, start checking at 15 minutes. Thicker pieces 1/2 inch or more may need 30-60 minutes. Let the clay cool completely before handling.

Test bake a few sample pieces to determine the ideal time for your project. Underbaked clay will not reach full hardness. Overbaked clay can become brittle and discolored. Adjust the time based on your specific clay and oven.

Physical Changes During Baking

Baking air dry clay causes some significant physical changes to the material. The most noticeable change is shrinkage. As the water evaporates out of the clay during baking, the material loses volume and becomes more dense. Expect up to 25% shrinkage of the original size depending on factors like temperature and bake time.

Along with shrinking, air dry clay will also change color when baked. The clay transforms from its original color, often gray or white, into terracotta tones like red, orange, or brown. This color change occurs due to chemical reactions as the material is fired. The clay will continue darkening the longer it bakes.

Texture is another aspect that transforms during the baking process. Unbaked clay is soft, malleable, and smooth. Baking makes the material harden into a ceramic, taking on a rough, gritty texture. The surface becomes more porous as well. These texture changes allow baked clay to be sanded, carved, and polished to achieve different finishes.

Chemical Changes During Baking

When air dry clay is baked, some key chemical changes occur within the material that transform it into a new ceramic substance. The most significant chemical changes include:

Evaporation of water – As the clay is heated, any remaining water that did not evaporate during air drying will be driven off as steam. This helps harden and strengthen the structure.

Activation of binder – Most air dry clays contain binders such as Portland cement, Kaolin clay, or vinyl polymer glues. Heat from baking causes these binders to cure fully, binding the clay particles into a rigid matrix.

Possible release of VOCs – Some air dry clays contain small amounts of solvents, plasticizers or other additives that can offgas as volatile organic compounds (VOCs) when baked. Proper ventilation is recommended if baking these clays.

Resulting Material Properties

When air dry clay is baked, the resulting material undergoes changes in its properties like strength, durability, and water resistance.

The baking process causes the clay to become much denser and harder as water evaporates out and bonds form between particles. This significantly increases the material’s strength and durability compared to regular air dry clay. Baked clay can withstand more pressure and force without cracking or crumbling.

Baking also makes the clay waterproof. The polymer chains that form during baking make it impervious to water, even when soaked. This is a major improvement over air dry clay, which can become soft again when exposed to moisture. The water resistance allows projects made with baked clay to be used outdoors or in wet environments.

Overall, baking transforms the clay into a much stronger, longer-lasting material. The resulting strength, durability, and waterproofness opens up more possibilities for creating lasting baked clay projects.

Usage and Safety Considerations

When baking air dry clay, there are some usage and safety considerations to keep in mind:

Food Safety

Baked air dry clay is not food safe, so any clay sculptures or items should not be used with food. The clay may contain chemicals that can leach into food, even after baking. Do not bake clay in the same oven or cookware used for food.

Fumes

Air dry clay can release fumes and odors when baked, especially at higher temperatures. Make sure the area is well-ventilated. Avoid breathing in fumes directly. Some clays may release more fumes than others.

Cleaning Bakeware

After baking clay, scrub any cookware or bakeware thoroughly before using it for food again. Clay can leave behind residue that should be removed. Avoid baking clay directly on oven racks.

Project Ideas for Baked Clay

Baked air dry clay can be used to create a variety of arts and crafts projects. Some ideas include:

Jewelry

Baked clay is lightweight and durable, making it ideal for jewelry pieces like beads, pendants, earrings, and more. Carefully shape, bake, and polish air dry clay to create unique jewelry components.

Figurines

Sculpt miniature figures, animals, dolls, and more out of air dry clay. Add small details before baking for a durable finished piece. Baked clay figurines make great gifts, collectibles, or home decor items.

Dishes

Handcrafted baked clay dishes like bowls, plates, mugs, and vases make artistic and functional pieces for the home. Securely attach handles and other accessories before baking.

Painting/Glazing Afterwards

After baking, air dry clay becomes less porous so acrylic paints can be used to decorate the surface. For shine and durability, apply a glaze before re-firing.

Summary

When air dry clay is baked, it undergoes both physical and chemical changes that alter its structure and properties. The baking process removes the water from the clay through evaporation, making it denser and harder. The clay particles fuse together into a permanent ceramic material that is no longer water-soluble. After baking, air dry clay has reduced flexibility but increased strength and durability.

The key takeaways for usage are that baked air dry clay can no longer be remolded or reused for modeling. The finished pieces will be hardened and more fragile, so take care not to drop them. Baked air dry clay is food-safe and durable for long-lasting decorative items, jewelry, dishes, and more. With proper baking times and temperatures, you can transform your air dried creations into permanent ceramic keepsakes.