Can Non Hardening Clay Harden?

Non-hardening clay, also known as non-drying clay, is a type of clay that does not harden or cure through drying. Unlike other clays that harden as the water evaporates, non-hardening clays maintain their soft, pliable texture even when completely dry. These clays remain permanently flexible and do not require baking or firing to achieve a hardened state.

The most common types of non-hardening modeling clays are oil-based clays like plasticine and polymer clays like Fimo. However, water-based clays made from natural materials can also be non-hardening. The key is their composition and properties that prevent hardening and cracking as they dry out.

Chemical Composition

Non-hardening clays consist primarily of materials like calcium carbonate, kaolin (china clay), and talc. They have high levels of components that prevent the clay from hardening and stabilizing its shape when exposed to air.

In contrast, clays that can harden and cure contain materials such as silica and grog that help form strong chemical bonds during firing or drying. Hardening clays have lower plasticity and higher grit content. The minerals present allow the clay particles to fuse and harden through heating or water evaporation.

Drying Process

Non-hardening clay, also known as plasticine or plastilina, dries out through evaporation. When exposed to air, the water and oils in the clay slowly evaporate over time, leaving the clay dried out but still malleable and soft.

This differs from traditional hardening clays like pottery clay that undergo a chemical reaction and harden through firing or baking. With non-hardening clays, no chemical reaction occurs so the clay remains pliable even when thoroughly dried out.

Non-hardening clays will gradually dry out on their own at room temperature over the course of weeks or months. However, the process can be sped up by heating the clay, either using a low oven, food dehydrator, or even a hair dryer. While the clay will become firmer as it dries, it will never fully harden.

Hardening Agents

While non hardening clay starts out malleable and soft, there are certain substances that can be added or used to harden the clay over time.

Some common hardening agents for non hardening clay include:

• Air – Exposing the clay to air allows it to dry out and harden over time. Non hardening clay that is air dried can take anywhere from 24 hours to 1 week to fully cure and harden.
• Oven – Baking the clay in an oven is another method for accelerating the hardening process. The clay should be baked between 225-275°F for 15-30 minutes to completely harden.
• Polymer clay liquid – Special polymer clay hardening liquids can be brushed or sprayed onto the clay to harden it. These liquids work by forming bonds between the clay particles.
• Mod Podge – Applying a layer of decoupage glue like Mod Podge can help harden and seal clay creations.
• Varnish or resin – Clear varnishes, resins, and other sealants can help harden and protect clay surfaces.

Experimenting with different hardening agents allows clay artists to achieve the specific finish and hardness desired for their creations.

Baking

Baking non-hardening clays at low temperatures can cause the clay to harden to some degree. When exposed to heat, the clay particles fuse together more tightly, which reduces the clay’s ability to re-wet and makes it harder when dry. However, non-hardening clays will still be somewhat flexible and prone to cracking when baked at low temperatures below 212°F (100°C).

Baking at higher temperatures between 230-265°F (110-130°C) will cause more significant hardening in non-hardening clays. The clay particles bond together firmly at these temperatures, creating a sturdy material when cooled. However, clays baked at high temperatures tend to become more brittle and are prone to cracking or shattering if dropped. Proper conditioning and molding techniques are necessary when working with clays hardened through high temperature baking.

While baking can induce some hardening, non-hardening clays will never become fully rigid like clays containing silicates or firing agents. The increased hardness from baking is limited, and the clays will still slowly soften and degrade over time with exposure to moisture. Baking can extend the usable lifespan of projects made with non-hardening clays if handled carefully.

Air Dry Clay

Air dry clay is a popular modeling material that can be shaped when wet but hardens as it dries. Unlike firing clays that require high heat to permanently harden, air dry clays dry and harden at room temperature. The main ingredients in air dry clay are water and natural materials like cellulose or plant starch.

When working with air dry clay, it can be easily molded into any shape. As it starts to dry, the water evaporates and it begins to harden while retaining its shape. The time it takes to completely dry and harden depends on factors like the thickness of the clay and humidity levels. Thinner pieces made with air dry clay will dry faster, while thicker pieces can take several days to fully harden.

Once completely dry, air dry clay is permanently hardened. The natural ingredients bind together as the water evaporates to create a durable, solid clay material. So while air dry clay starts out soft, it can fully harden at room temperature without any special treatment needed. This permanent hardening allows air dry clay to be used to create lasting sculptures, ornaments, jewelry and more.

Polymer Clay

Polymer clay is made from polymers like polyvinyl chloride (PVC) combined with plasticizers and coloring pigments. The exact recipes vary between brands, but the core ingredients are PVC resin and plasticizers. The plasticizers keep the clay soft and malleable at room temperature.

Unlike air dry clay, polymer clay does harden and become permanent once baked. The plasticizers evaporate when baked at the recommended temperature, causing the PVC molecules to bind together into a hardened plastic. So although polymer clay remains flexible and workable at room temperature, it can permanently harden when baked. Properly baked polymer clay is durable and waterproof.

The baking process, usually 275°F – 325°F for 15 minutes per 1⁄4 inch of thickness, transforms the polymer clay from its temporary state into a permanently hardened material. So yes, polymer clay will harden through baking even though it remains flexible at room temperature before being cured in an oven.

Other Clays

Besides air dry clay and polymer clay, there are other types of clays that are considered non-hardening. One such clay is cold porcelain, sometimes called “cold porcelain clay.” Cold porcelain is made from cornstarch, glue, and baby oil or mineral oil. It has a smooth, doughy texture that is easy to sculpt and shape.

Cold porcelain does technically harden over time when exposed to air. However, it hardens extremely slowly compared to clays containing cement or plaster. Pieces made from cold porcelain can take weeks or even months to fully harden and cure. The hardening process can also be sped up by placing items in the oven on a low temperature setting.

While cold porcelain will eventually achieve an almost ceramic-like hardness, it is still considered a non-hardening clay because of the very slow hardening process. Many crafters and artists prefer to use it in its soft state for decorations, jewelry, dolls and other soft sculpture. So while it does harden slightly over time, cold porcelain is generally treated as a non-hardening clay in practice.

Uses

Non-hardening clays like polymer clay and air dry clay are popular for crafts and art projects because they don’t require firing or baking to harden. Here are some common uses for non-hardening clays:

Crafts

Non-hardening clays work wonderfully for homemade crafts. Polymer clay can be sculpted and then hardened at home by baking it at relatively low temperatures. Air dry clays simply harden through evaporation and don’t require baking at all. Popular crafts include:

• Jewelry – beads, pendants, charms, earrings
• Figurines – animals, dolls, miniatures
• Decor – bowls, vases, boxes, wall hangings
• Ornaments – seasonal, holiday, custom designs

The finished clay crafts can be painted or embellished after hardening for colorful, professional-looking results.

Kid’s projects

Clays that don’t require high heat or firing are ideal for children’s art projects. Kids can sculpt and shape the clay, then allow projects to harden/cure at room temperature. Non-hardening clays are mess-free, non-toxic, and easy for little hands to manipulate. Great kids’ projects include:

• DIY toys – animals, action figures, dollhouse items
• Games – clay jewelry, miniatures for pretend play
• Arts and crafts – beads, pins, magnets, boxes
• Seasonal – ornaments, decorations, gifts

With supervision, even very young kids can safely work with non-hardening clays for hours of creative fun.

Conclusion

In summary, while some clays like air dry clay and polymer clay can harden without heat, most non-hardening clays require additional steps to fully harden them. Baking them at the right temperature or adding hardening agents are two common ways to make non-hardening clays permanently hard. Each type of clay has its own chemical composition, which impacts the hardening process. Overall, with the right treatment nearly all clays can be transformed into a hardened, durable state suitable for a variety of uses. By understanding the options available, artists can choose the clay that fits their project needs and harden it to create lasting works.