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ceramics

  • What to Know About Ceramics

    Everything you wanted to know about clay, and its other forms

     

    What is Clay

    Clay is made up of the finest rock particles that are eroded by wind and rain. These particles usually build up on the bottom of rivers and lakes where they stick together and form into clay consistency. Clay is a very versatile material and has several different states from liquid to rock-like hardness.

    What is Ceramics

    Ceramic is the ‘final’ state of clay, when its chemical composition changes after being put through a high temperature firing. Clay in this form is no longer dissolves in water, it’s heat resistant, corrosion resistant but still brittle.

    Important Terms

    • Wet Clay - mixed clay that is elastic and ready to be formed.
    • Leather-hard - the stage of the drying process when the clay is hard enough to be handled without altering its shape but it's still possible to work with it.
    • Greenware - the sate of the clay when it's dry but still not ready to be fired.
    • Bone dry - fully dried clay that is ready to be fired. at this stage the clay is very brittle.
    • Bisque - the first firing, that makes the surface porous so the surface can absorb the glaze.
    • Grog - a sand-like substance that's added to the clay to help workability, to reduce shrinkage and add strength.

    Classes of Clay Body

    There are many different types of clays available, and it’s important to chose the best for your projects, as each type has different qualities, and what works for pottery might not be the best for sculpting.

    Earthenware

       

    Earthenware clays are the oldest and most common type of clay. They are easy to work with, and because they contain iron and other minerals it’s possible to be fired at a lower temperature (between 950°C and 1100°C). This means that they are more fragile than other clay types, can’t really hold liquids if unglazed, but glaze colours are a lot more vivid than stoneware ceramics’.

    Naturally they are red, orange, yellow or light gray, and once fired they have a brown, red, orange, buff, gray or white colour.

    Stoneware

    Stoneware clays share similarities with stone once fired – as in hard surface. Stoneware ceramics are excellent for functional items like dinnerware, as they can hold liquids and are more durable. Their firing temperature ranges from 1180 °C to 1280 °C. Stoneware clays are usually gray or brown.

    Porcelain

    Porcelain and kaolin are considered the best type of clays for pottery. They are largely made up of silicate and are resistant to high temperatures. As porcelain is made up of fine particles, it’s very smooth and can be used to create extremely thin forms. It’s relatively difficult to work with because of its low plasticity. It’s also quite delicate before firing as its optimum density is only achieved before its melting point. Porcelain’s firing temperature is up to 1,400 °C. It’s characteristically white or light coloured unless it’s been mixed.

    Forming

    • Slab Building - Slab building is a technique where the clay slabs are rolled or pounded flat in order to use them for constructing objects.

    • Hand-building - Hand-building is quite literally forming objects out of clay with your hands. Clay portraits are a good example of purely hand-made forms.

    • Coiling - Coiling is a good beginner technique that's suitable for both pottery and sculpture. Coiled pots are built up with rolled up clay in a spiral. Read more 

    • Throwing - Throwing means the technique of using a pottery wheel that keeps the clay spinning, thus making it possible to create symmetrical vessels.

    Firing

    There are two main types of firing, Bisque firing and Glaze firing. Bisque firing is the first firing the clay goes through after it reached the ‘bone dry’ stage. During bisque firing all the chemicals and organic residue burn out of the clay. After this first firing the clay becomes ceramic; it hardens into a rock-like consistency that’s no longer dissolves in water. Its surface becomes porous, perfect for the glaze to adhere to.

    Shrinkage

    It’s worth knowing that clay shrinks when it dries and then when it’s fired for the first time. Shrinkage depends on the specific type of clay and can vary between 4% to 15%

    Glazing

    Ceramic glazes come in many different colours and types, from transparent to opaque, matt or glossy, cracking or metal effect.

    While you can experiment a lot with different combinations, there are some basics to note.

    Glazes are basically glass melted onto the ceramic object. In order to stick evenly to the surface, glass is mixed with different components and binders. Glazes come in powder form that you need to mix yourself and as liquids that are ready to use.

    In general glazes not only add colour or ‘shine’ to your pieces, but makes the ceramic object vitreous, and seals the clay so it becomes able to hold liquids and depending on the glaze, food safe.

    Glaze Firing

    Glaze firing is usually done in a higher temperature than bisque, and it finishes the process of making a ceramic object. It’s a faster firing process than bisque as by this time the clay body doesn’t contain as much water; what happens during glaze firing is that the glass melts and solidifies on the object. It’s important that the glazed object doesn’t touch other objects or the surface of the kiln as it will be glued together. To avoid this, make sure to place each object at least an inch apart, and to leave the parts that touch the kiln unglazed. You can either use wax to leave unglazed surfaces or just wipe off the excess with a wet sponge.

     

    If you want to try ceramics in Dundee, make sure to check out the Dundee Ceramics Workshop!

    References

    https://skutt.com/skutt-resources/basic-knowledge/ceramics/ceramics-101/

    http://www.lakesidepottery.com/Pages/Pottery-tips/choosing-the-right-clay-type.htm

    http://www.lakesidepottery.com/Pages/Pottery-tips/Throwing-a-pot-Lakeside-Pottery-Tutorial.htm

    https://www.artistsandillustrators.co.uk/how-to/sculpture/252/beginners-guide-to-sculpting-in-clay

  • Ceramics: Pinch Pots

    Possibly the most ancient and also the most accessible and simple method of making a clay pot is the Pinch technique. People have been making pinch pots for thousands of years, as it requires only a ball of clay and your own two hands.

    Getting Started Pinching your Clay

    To begin making your pinch pot, simply take your ball of clay and roll it around in your hands,  kneading it like dough on your worktop. This will warm up your clay allowing it to me moulded easily.

    Push your thumb into the centre and begin to pinch the clay, opening out the mouth of your pot. This is a very tactile technique and only requires you to keep shaping your pot with your thumb and fingers until you are happy with your shape. You can also add handles, or faces or whatever you like to personalise your pot.

    Here's a great tutorial demonstrating the ease of this technique.

    You can now decorate your pot with various under glazes, or you could allow it to sit overnight until it is 'leather dry' (a term describing partially dried clay that will allow you to work into the surface without altering the shape or structure of your creation). Once 'leather dry' you have the option to smooth the interior and exterior, trim the lip of your pot or carve a design into the clay.

    You don't have to stop at pinch pots, however, you can used this technique to make anything you can imagine from cups to strange creatures. Here are some different examples of the results you can achieve!

     

     

    www.galatiak12art.blogspot.co.uk/2016/02/art-i-pinch-pots.html
    www.youtube.com/watch?v=2CQAdMxjBik
    www.kathyjeffersstudio.com/pottery/pinch-pot/
    www.juliannakunstler.com/ceram1_pinchpot.html#.WUumiOvyu00
    www.jennygulchpottery.wordpress.com/2008/09/13/

  • Ceramics: Coiling

    Ceramics Coiling...Explained

    Coiling is a very straightforward ceramic technique that can produce fantastic results, from simple pots to intricate vessels. Evidence of this technique has been discovered all over the world showing many ancient civilisations having used clay in this way, from China and Japan to Africa, Greece and Mexico.

      

    The Process of Coiling Clay

    Using the coiling process you start with just the base of your vessel and you build up layer upon layer of clay using long sausage-like shapes around the circumference of your base. This technique allows you to control the thickness of the clay walls and also means that the design and shape can be planned and developed from the very start. The interior and exterior of your clay creation can be smoothed over or you can keep the the coils depending on your desired aesthetic.

    You want to start off by kneading your ball of clay with a decent amount of pressure to try and force out any trapped air, then the clay can be rolled out flat and evenly with a rolling pin. Using a template you can cut out a shape to become the base of your pot. From here you simply roll out sausage shaped coils of clay and begin building up your layers; merging, cutting and shaping them as you go. Slip should be used as well as scoring the clay in between each coil layer to act as a glue to hold the coils together

    Cutting coils - Click this image for a full step by step tutorial

    This is repeated to the desired height and shape of your vase, bowl or pot. You may wish to smooth the the interior and exterior depending on your desired result.

    You do not have to stick to this design; coiling can be a very versatile technique, check out some of these examples of more intricate designs!

      

    Also check out this time-lapse of the process!

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