What Is The Difference Between Self Hardening Clay And Air Dry Clay?

ByScarlett Evans

Clay comes in many varieties for artists and crafters. Two common types are self-hardening clay and air-dry clay. While both clays harden without baking, they have some key differences. This article will provide an overview of self-hardening and air-dry clays, comparing their composition, drying process, working properties, availability, cost, and best uses for projects.

Definitions

Self-hardening clay, also known as pottery or ceramic clay, is made from natural clays and minerals that have been purified and combined. Self-hardening clay hardens naturally due to the chemical processes inherent in the clay, without needing to be heated. Once shape and harden, self-hardening clay exhibits the properties of finished ceramics, becoming vitrified, impermeable to water, and strong.

Air-dry clay is a modeling material made from a man-made plastic polymer, such as polyvinyl acetate. It dries by dehydration and hardens at room temperature. Air-dry clay remains flexible if sealed after drying and can be manipulated and reshaped over and over again by adding water.

Composition

Air dry clay, also known as self-hardening clay, is made from natural clays, such as pottery clay or ceramic clay. According to Activa Products, air dry clay is composed of natural clay, calcium carbonate, organic dye, and cellulose-based binders [1]. These ingredients allow the clay to dry and harden at room temperature.

In contrast, polymer clay contains polyvinyl chloride (PVC), which allows it to harden when baked in the oven rather than air dried. Polymer clay is made from a plasticized PVC resin and contains no natural clays according to the polymer clay website [2]. The compositions give each type of clay distinct working properties and uses.

Drying Process

The key difference between self-hardening clay and air-dry clay is in the drying process. Self-hardening clay contains Portland cement which enables it to naturally harden and cure over time when exposed to air. The clay undergoes a chemical reaction that causes it to harden from the inside out. This means self-hardening clay does not require baking or firing and will dry on its own at room temperature over 24-72 hours.

air dry clay drying and self-hardening clay in a chemical reaction

Air-dry clay, on the other hand, dries through the evaporation of water rather than a chemical reaction. Air-dry clay hardens as moisture evaporates and leaves the clay, allowing the particles to come closer together. Proper drying requires adequate ventilation and takes 1-3 days at room temperature. Air-dry clay will not completely harden or reach maximum strength if improperly dried.

While self-hardening clay cures evenly throughout, air-dry clay tends to dry from the outside in. This can lead to cracking if the exterior dries too quickly. Air-dry clay may also shrink slightly as it dries. Self-hardening clays experience minimal shrinkage. Overall, the chemical hardening process of self-hardening clay leads to less cracking and more uniform results.

Working Properties

Self-hardening clay is very smooth and flexible when first opened. It has a soft, velvety texture that becomes firmer and less malleable as it dries. The clay can be easily shaped by hand without sticking. Self-hardening clays are lightweight and easy to work with. Pieces dry slowly over the course of 24-48 hours and can be carved, cut, or sanded after drying.

Air dry clay has a smooth, clay-like texture when opened but still retains some flexibility when dry. It has good workability for sculpting and handbuilding. Air dry clay can be rolled, cut, shaped, molded and impressed while still soft. It will not dry out quickly while working with it. The surface becomes harder as it dries over 1-3 days but can still be sanded or carved after drying. Air dry clays are heavier than self-hardening clays.

Overall, self-hardening clays have a silkier texture for fine detailing while air dry clays mimic the dense feel and handling of fired ceramics more closely. Both offer good workability and ample working time before drying begins.

Best Uses

Air dry clay is best for making crafts, jewelry, miniatures, dollhouse items, and pieces that don’t need to be durable or withstand much handling. Some examples of air dry clay uses include earrings, ornaments, small decorative items, elementary school art projects, and items that will be painted and sealed after drying. Air dry clay is easy to work with, non-toxic, and convenient since items can dry at room temperature without requiring an oven.

Self-hardening clay is ideal for more robust pieces that need structural integrity. It is commonly used for model trains, architectural models, sculptures, figurines, dioramas, and parts that may be subjected to more wear and tear over time. For instance, self-hardening clay could make durable arms or legs on a figurine that protrude and may easily break if made with weaker air dry clay. Self-hardening clays create strong, long-lasting finished products perfect for collectors, artists selling their work, or projects requiring more permanence.

Availability

Self-hardening clay can be purchased at most craft stores, art supply stores, and online retailers like Amazon and Blick Art Materials. Some popular brands of self-hardening clay include Amaco’s Marblex and Primo. It’s usually sold in bulk packages.

Air dry clay is also widely available at the same locations – craft stores, art supply shops, and online. Brands like Crayola Model Magic and Activa Air Dry Clay are commonly found. Air dry clay often comes in smaller packaged amounts geared towards kids’ crafts and modeling.

According to Susie Benes, an expert polymer clay artist, air dry clays like Makin’s Clay have similar working properties to polymer clay while also being easy to purchase at local craft stores. This makes it a good option for beginners looking to start sculpting at home without ordering clay online.[1]

Cost

In general, self-hardening clays tend to cost less per pound than air-dry clays. Self-hardening clays like pottery clay start around $5 for a 20 pound bag, while air-dry clays like Creative Paperclay cost around $16 per pound (https://www.susiebenes.com/blogs/airdryclayart/an-artists-choice-epoxy-or-air-dry-clay-for-sculpture). The reason for this price difference is the manufacturing process – air-dry clays go through more steps to be lightweight and smooth which increases the costs. However, because air-dry clays are very lightweight, you tend to use less clay overall for a project. So the total cost difference may not be as significant as the per-pound price implies.

When deciding on a clay, it’s important to factor in the cost per project rather than just per-pound. The amount of clay needed and the number of projects you plan to make will determine if the extra cost is worthwhile. For small sculptures and detailed work, air-dry clays excel and may justify the higher price. For large volume projects, self-hardening clays will be the more budget-friendly option.

Projects

Both self-hardening clay and air dry clay can be used for a variety of creative projects. Here are some ideas for each type of clay:

Self-Hardening Clay Project Ideas

Self-hardening clay is great for detailed sculptures, jewelry, and decorative items. Project ideas include:

Air Dry Clay Project Ideas

Air dry clay is ideal for larger sculptural works as well as kids’ crafts. Project ideas include:

Conclusion

To summarize, the main differences between self-hardening clay and air-dry clay come down to their composition and drying process. Self-hardening clay is made from natural clay minerals and hardens through a chemical reaction when exposed to air. It does not require baking or firing to fully harden. Air-dry clay is made from non-clay materials like cellulose compounds and hardens simply through evaporation as moisture evaporates when exposed to air. It also does not require baking or firing.

In terms of uses, self-hardening clay is best for items that need to be more durable and hold up to more wear, like pottery and sculpture. Air-dry clay is best for craft projects, jewelry, decorative pieces, and items for display. Both clays are widely available at craft stores and online at affordable prices. With some basic knowledge of their properties and differences, both can be used successfully for a variety of fun and creative projects.

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