What Softens Hard Clay?

Hard clay is a type of dense clay that contains minimal amounts of sand or silt particles. It has low porosity and becomes very stiff and rock-like when dry. Hard clay has high cohesion and plasticity making it prone to cracking and difficult to mold or shape. These properties are due to the layered crystalline structure of the fine clay particles that stack closely together.

In pottery and ceramics, hard clay is difficult to work with in its dry, natural state. The hardness prevents proper shaping of the clay body and leads to cracking and breakage. That’s why prior to throwing, molding, or sculpting, hard clays must be softened to make them more malleable and workable. The aim is to reduce stiffness and increase plasticity so the clay can be formed into smooth shapes without cracking or tearing while maintaining enough structural integrity to hold its form without slumping or deforming.

Water

Water is one of the most readily available and effective ways to soften clay. Adding water to clay allows it to be absorbed into the clay body, which causes the clay particles to move apart from each other. This creates more space between the particles, allowing them to move and shift more freely, resulting in a softer and more malleable clay.

The amount of water to add depends on how soft you want the clay to become. For slight softening, start by adding a teaspoon at a time and kneading it into the clay. For maximum softening, you may need to add up to 1/4 cup of water per 1 pound of clay. Add the water gradually and knead thoroughly between additions to ensure even absorption.

Too much water can make the clay sticky and difficult to work with, so add conservatively. If the clay becomes too wet, allow it to dry slightly before continuing to soften it. The optimal consistency is smooth, flexible, and pliable without being sticky.

Vinegar

Vinegar is a common household ingredient that can be used to soften clay. Vinegar is an acidic liquid that lowers the pH of clay when added to it. The acidic properties of vinegar work to break down the molecules in the clay that make it hard. Using vinegar to soak clay will slowly dissolve the minerals and soften up the clay over time.

To soften clay with vinegar, start by mixing 1 part vinegar to 2 parts water. You’ll want to use an old bowl or container, as the vinegar can stain. Add clay pieces or clay powder to the vinegar-water mixture. The amounts aren’t as important, but make sure the clay is fully submerged. Let the clay soak for at least 24 hours. Check it periodically and stir to expose all sides to the vinegar water. The clay should slowly start to soften up over time.

For very hard clay, you may need to increase the ratio of vinegar, doing 2 parts vinegar to 1 part water. Let it soak for 72 hours, stirring occasionally. Test the softness and add more time if needed. Once the clay is soft, remove it from the vinegar soak and rinse it well. Knead it for a few minutes to remove any lingering vinegar. The clay is now softened and ready to use for any project.

Vegetable Oil

Vegetable oil is another common household item that can be used to soften clay. Oils work by coating the clay particles and filling in the spaces between them, helping the particles slide past each other more easily and making the clay more malleable.

When using vegetable oil to soften clay, it’s recommended to use a pure oil without any added ingredients. Good options are canola oil, sunflower oil, or safflower oil. Avoid using olive oil, which can leave an odor in the clay. Start by adding just a small amount of oil, such as 1/2 teaspoon per 1/4 pound of clay. Knead the oil into the clay until it reaches the desired consistency. Be careful not to add too much oil, as this can make the clay sticky.

Vegetable oils are very effective at softening clay quickly. Just a small amount of oil goes a long way in improving the clay’s workability. Oils also leave no discoloration or residue behind. Just be aware that oils can sometimes interfere with clay projects that require baking or firing at high temperatures.

Glycerin

Glycerin is an effective yet often overlooked method for softening clay without making it sticky. It is a clear, odorless liquid that has a syrup-like consistency. When added to clay, glycerin penetrates between the clay particles and makes the clay more flexible and workable.

The amount of glycerin needed will depend on the type and dryness of the clay. As a general guideline, start by mixing 1-2 teaspoons of glycerin per 1 pound of clay. Knead the glycerin into the clay until it reaches the desired consistency. Adding too much glycerin can make the clay too soft or sticky, so it’s best to add it gradually.

One of the benefits of using glycerin is that it does not alter the color or properties of the clay. It also helps prevent cracks and breakage when baking or firing clay sculptures. Unlike water, glycerin will not evaporate so its softening effects last longer. Glycerin is safe, non-toxic and washes out of finished pieces easily.

Commercial Softeners

There are several commercial products designed specifically to soften hard clay soils. These products work by modifying the clay’s chemical structure, making it less sticky and more workable. Two of the most common commercial clay softeners are:

Darvan 7

Darvan 7 is sodium polymethaphosphate, a long chain phosphate polymer. It works by dispersing the clay particles and preventing them from sticking together. To use Darvan 7, make a concentrated solution by mixing 1 part Darvan 7 with 4 parts water. Apply this solution at a rate of 1-2 quarts per 100 lbs of dry clay. Mix thoroughly and allow it to soak in for several hours before working with the clay.

Sodium Silicate

Sodium silicate, also known as water glass, is a compound of sodium oxide and silica. When added to clay, the sodium ions displace water molecules from the clay structure. This allows the clay particles to move more freely instead of sticking together. Sodium silicate powder can be mixed into clay at a rate of 5-10% by weight. Liquid sodium silicate can also be diluted with water and spritzed directly onto clay.

These commercial softeners work quickly and effectively to transform sticky, stubborn clay into a smooth, workable material. They allow crafters and artists to successfully use native clays that would otherwise be too difficult to work with.

Freezing

Freezing clay and then allowing it to thaw is an effective method for softening it. When water freezes it expands, and this expansion creates small cracks and spaces in the clay. When the frozen clay is allowed to thaw, the melted ice water is then able to seep further into these spaces which softens the clay.

To soften clay by freezing:

• Place the clay in a sealed plastic bag, removing as much air as possible.
• Put the bag of clay in the freezer and freeze overnight or for at least 12-24 hours.
• Remove the frozen clay from the freezer and allow it to completely thaw at room temperature. This may take several hours.
• Knead the thawed clay briefly to distribute the moisture. The clay should now be softened.

Freezing allows time for water to fully penetrate the clay and expand into any hardened areas. Letting the clay completely thaw ensures the moisture is distributed evenly. This technique can quickly and effectively soften even very stiff, dried out clay.

Beating/Kneading

Beating and kneading clay produces a mechanical action that helps soften and align the clay particles. As you apply force and manipulate the clay, the plate-like particles slide over one another and become stacked in a more orderly fashion. This alignment allows water to more easily penetrate between the spaces in the clay.

When kneading by hand, press, fold, and push the clay repeatedly to realign the particles. Use the heels of your hands to apply pressure as you squeeze and push the clay across a hard surface. Kneading for 10-15 minutes can significantly improve workability. For larger quantities, a stand mixer with a dough hook attachment can vigorously knead the clay. Avoid over-kneading which can incorporate too much air.

Beating uses tools like a rolling pin, paddle, or mallet to pound and compress clay. The impacts from beating physically break apart clay chunks and slides particles into alignment. Start with lighter tapping, then increase force. Fold and turn the clay periodically while beating to expose all areas to the mechanical action. Wood and plastic tools are gentler than metal ones when beating clay.

Stomping

Stomping clay with bare feet is an age-old method for softening and conditioning clay. As you march and stomp on the clay, the force from your feet compresses and squeezes the clay. This pressure breaks up the clay’s structure on a microscopic level, allowing more water to penetrate into the clay particles.

The physical manipulation also aligns the clay particles, increasing its plasticity and making it smoother and more malleable. Much like kneading bread dough, the action of stomping develops the clay’s elasticity. The warmth from bare feet also slightly raises the clay’s temperature, which promotes softening.

Stomping is an easy, low-cost way to soften clay, though it can be messy. Make sure to lay down plastic sheeting or do it outside. The finished clay will be homogenized and any hard lumps or dry patches will be softened out. Just a few minutes of stomping can make a big difference in the clay’s workability.

Conclusion

There are many effective ways to soften hard clay for sculpting and ceramics work. Adding water is a simple method that works for most clays. For extremely hard clay, vinegar can help break down minerals and draw out more moisture. Oils like vegetable oil or glycerin act as plasticizers to keep clay flexible after drying. Commercial clay softeners are another option, just follow label instructions carefully.

Freezing, beating, kneading, and stomping clay can also help realign clay particles and improve workability. The best practices for softening clay depend on the project and type of clay you are using. Test different methods to find what works best for your needs. In general, natural additives like oil and vinegar are gentle options. Commercial softeners will produce more dramatic effects but may alter clay properties. Whichever softening method you choose, work carefully to achieve optimal flexibility without compromising clay strength.