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glaze

  • 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

  • INTRODUCING ROYAL TALENS COBRA – THE WATER MIXABLE OIL PAINT

    What does water - mixable oil mean?

    Literally, it is possible to mix the Cobra oil series with water, without losing the properties of regular oil paints. Cobra oils contain the exact same materials as regular oil paints; the difference is that they are modified in order to mix with water.  Since they do contain oils, it is important to keep that in mind that they still can be mixed with turps and spirits as well, so when you’re using water you have to mix them little by little to enable the particles to mix well.

    (They can also be mixed with regular oil paints, but then they lose their ability to mix with water!)

     Why is Cobra good?

    Having a paint that has the same properties as traditional oil paints, but is also mixable with water has many advantages. Firstly, you don’t have to use harmful chemicals like turps and spirits, thus you don’t have to buy, carry and smell them in order to produce oil paintings. Secondly, since you’re only using water, it is safe to pour the remnants into the sink, making your life easier, as well as not having to worry about environmental damage.

    Thirdly, you don’t have to throw away your non-water soluble oil paints, as Cobra paints can be mixed with them.

    Get to know what artists think!

    Things to keep in mind with Cobra Solvent Free Oil Paint

     Artist and Study Quality

    Artist Quality
    Study Quality

    There are two types of the Cobra oil paints available – artist and study quality.

    The main difference between the two is that the artist quality paints consist of equal amount of pigments and binder, while study quality paints contain half of the amount of pigment with an additional material called extender. This way, it’s possible to create cheaper, but still good quality paint.

    Paint series

    You may also notice that the artist quality brand has 4 series that also have different prices. This is due to the fact that certain pigments are more difficult to get hold of, therefore their production costs are higher – it does not indicate that the more expensive colours are any better!

    The series numbers are indicated on the back of the tube!

    Mixing Colours

    Not surprisingly, the question whether Cobra oils and acrylics can be mixed may arise, and of course, both paints can be mixed with water! However, even though it is possible to mix them, it is not advised in the long run, as the drying process of water based paints is completely different to oil based paints. While acrylic paints remain flexible due to their plastic content, oil paints dry harder with age, resulting in cracking and other different damages of the painting.

    Cobra Painting Medium

    Building up a painting with the Cobra series works the same way as with regular oils – the principle of the “fat over lean” technique still applies. With this technique, you add your layers that should contain less and less solvent (water), which means more paint, thus more oil goes to the surface. However, if you don’t wish to use paint straight out of the tube for the last layer, or wish to have a very smooth effect, the Cobra Painting Medium is what you need.
    To make the fat over lean principle work, you will have to add more and more medium into the water you’re mixing with, this way the solvent will contain more oil even without adding very thick layers of paint.

    Glazing with Cobra

    Glazing is the application of a very transparent layer of paint on top of the others.

    The Cobra Glazing Medium is very similar to the Painting Medium, with the difference being that it doesn’t contain any water, so it is more flexible. The Glazing medium has to be applied directly out of the bottle to the last layer of the painting.

    Another possible way to use it is to put subtle colours into black and white paintings, by mixing the glazing medium with paint and applying it to the surface of the dried painting. This way the original brushstrokes remain untouched, and you can put on more colours or brush them off without affecting the finished painting.

    Cobra Odourless Spray Varnishes:

    Varnishes are applied in order to protect the painting from ageing as much as possible. It’s important to keep in mind that varnishing has to be done after at least a year has passed since the finishing of the work to allow the oils to dry properly.

    Other Properties of Cobra Oil Paints:

    Study Quality

    Artist Quality

    References:

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