Removing dried clay stains is easier than you'd think. Since it's already dry, there's probably no excess to brush off, so you should go straight for pre-treating the garment in a solution of laundry detergent mixed with water. Finally, wash the garment as usual. Repeat the process if the stain is persistent.
I got good results by using Dithionite in a bufferen solution. The clay is stabilised by the iron ions. The dithionite solves the iron in the clay and makes the clay soft and friable. After that you can remove it by an old tooth brush.
If you have larger pieces that have completely dried, or old unpainted projects you want to reuse, you can still revive the clay. Break the dried clay into smaller pieces. Soak the pieces in a container overnight. Drain the excess water and work the clay into a ball.
If that doesn't work, try placing a hot water bottle over the clay for 15- 20 minutes. Rolling the clay back and forth in your hands will also warm it up. Once it starts to soften, keep going and roll it into a ball and then a snake. Knead and twist it, and keep doing this until the clay is fully conditioned.
Coating with water
It makes a huge difference! You can repeat this process a few times. Wait for the clay to dry completely, gently sand it with super-fine sandpaper again and coat with water one more time. I usually do it just once and repeat only on the areas with still visible fluff.
You can sand air-dry clay to smooth the surface of your sculpture. When sanding air dry clay it is important to use fine-grit sandpaper. Clay is easily sanded and a rougher grit could remove more material than you'd like.
Vinegar can also be used to break down clay soil. The vinegar's acetic acid helps dissolve clay particles, making the soil easier to work with. Earthworms are also beneficial for breaking down clay soil.
If you prefer trying alternative methods for clay stains, instead of a soaking solution you could try mixing a cup of white vinegar with three tablespoons of salt and putting it onto the stain for 30 minutes. When the time's up, wash your garment as usual, and repeat the steps if the stain is not completely removed.
What does vinegar do to clay? The acidity of vinegar breaks down the clay and makes it sticky. Some artists use vinegar straight from the bottle, or add vinegar to clay instead of water to make a joining slip and add also you can use white vinegar to clay slip to break down the clay particles faster and make it .
It is well known that hydrofluoric acid rapidly dissolves silica, clay and mixtures of silica and clay.
To remove bubbles, rub very gently and lightly (this will help you to avoid white streaks) across the bubble with the cotton bud (Q-tip), alternating the directions you're rubbing in. If you rub in the same direction for too long, the acetone will dissolve the clay and you'll be left with a groove.
Clay must be fired in a kiln to harden, while modeling clay will harden. This means that clay sculptures are more permanent than modeling clay.
It may take a long time for the clay to smooth out and mix completely with a pasta machine. Warming your clay helps make this easier. Use body heat, or a heating pad, or submerge clay (in a baggie) into hot tap water. Craft store clay is often hard when you buy it due to slower turnover.
Petroleum Jelly
The second polymer clay tip, vaseline does miracles to clay.
Sanding
Believe it or not, it is possible to sand air dry clay. Once your clay has dried completely and hardened, you can use a piece of sand paper to smooth out any sharp edges. You may want to start with a small grit to refine any rough edges before gradually increasing the grit to a finer level to polish the clay.
Clay trimmings will (usually) be leather hard or softer, meaning they can be gathered up and placed into a container without creating dust, which is not the case if you let them fully dry first. Never sand pieces dry, always add water. The water catches the fine particles and you get a paste instead of dust.
Hydration occurs as clay packets absorb water and swell. Dispersion (or disaggregation) causes clay platelets to break apart and disperse into the water due to loss of attractive forces as water forces the platelets farther apart.
Clay- based soil is made up of small, compacted, flat particles. You will notice that these particles are slippery when wet and hard when they are dry. Clay does not let water penetrate it easily, but once it does penetrate, it retains this moisture.