“Hand” building

First, make two pinch pots. The rims shouldn’t be too thin then join them together. Roll another lump of clay as the wrist and also it is the base of the hand. After the hand has been built some of the clay in the middle of the wrist will be removed  as it is too thick it would be broken during the firing.

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use any carving tool make lines on the feet surface in order to divide sections. Gradually add in details of a feet.

100_2854 OUCHHHHHH!!

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Clay Project – Year 1

Simple introduction of how clay is formed  – it is believed that is the most common and abundant raw material in the earth. It is an end product of the geologic weathering of the earth’s surface. In remote geological time our earth was a molten mass of material covered by a thin layer of earth crust. Gradually, the geology changed and the earth started to cool off. The molten mass on the upper layer solidified to a much thicker earth crust and rocks were formed called igneous rocks. As the earth cooled off the moisture in the atmosphere also become more dense, then torrential rain began and has lasted for millions of years. The rain water has a profound effect on the clay’s formation. Water seeps though cracks of rocks and it expands when it freezes, the rocks are broken into small pieces. These small rocks continue to undergo abrasion and grinding by water or wind borne weathering, and break into even smaller pieces then to fine particles. Water continues weathering these particles making them even finer and are carried away from where they are original formed until finally laid down in the estuaries or deltas as clay.

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The Clay Project

The first project from the tutor is to understand the physical properties of unrefined clay. We have been asked to collect some local clay. It could be found in tidal estuaries, rivers banks, building sites, beaches or in our own back garden. It is rarely found on the surface where usually is sand or mud. The clay should be slightly moist and malleable. So we need to dig at least 40 cm deep below the surface. As the clay has not been processed, pebbles, roots, leaves, stones or sand may be found in the clay. These pictures were taken at a building site on Colchester Avenue, Penylan. A deep hole was dug and the clay is still moist. With the permission of the site’s builder I was able to get the clay easily. In these pictures you can see the clay is rusty brown colour so it should be contained iron. 

100_2712 Back at the workshop I crumbled the clay and discarded the large-sized rocks and pebbles then placed them on a bat. I found that to place a piece of newspaper underneath the clay not only helps the clay dry more quickly, due to it’s water absorption ability, but it also makes it easier to transfer the clay to a bucket later.   After the clay is completely dried transfer it to a bucket and fill it with water. The water should be just enough to cover the clay. Allow the clay to soak in the water until it has turned soft, then pour off the excess water. At this stage the clay should be a thick paste-like texture but still have small stones and sand which need to be separated. I used #40 mesh sieve to sift the clay. a brush or rubber rib will help to push the clay through the sieve. If necessary other tools can be used for helping to push through the big lumps.

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The sifted clay looks like slip. If it is too wet, coil some clay round the edge of a plaster bat to prevent it slopping out.

This is my clay and it was not too runny so I poured it onto a plaster bat directly without coiling the edges,100_2734 then spread it out and smoothed the surface a bit. The reason for using a plaster bat is its water absorption ability and also the clay won’t stick to its surface. It took about 15-20 mins to become stiff. I would suggest checking it occasionally sometimes the slip can turn stiff fairly quickly. When the slip has stiff on one side, turn it over to allow the plaster bat to plays its part on the other side. As long as the clay has reached the right consistency, wedge and knead it then it is ready to use.

100_2872We can check the plasticity of the clay by rolling coils and bending them into tight curves to see if they crack easily. To check shrinkage percentage, rolled out six strips of clay into 12 cm long and scored a 10 cm line on each one. Marked down on each strip a firing temperature of 1000℃, 1100℃, 1200℃, 1260℃ oxidation and 1260℃ reduction and a strip marked as ‘raw material’ to check the clay shrinkage percentage as it will decrease in size after it has dried. An extra 100g of clay was measured out for checking it’s weight changed after drying.

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After firing, the clay strips showed different colours. These colours are usually produced by iron oxide. Due to different firing temperature and the atmosphere in the kiln the clay body will produce various tones of colours, they could be from light pink, yellow, orange, red, brown, dark brown to black.

In a plastic clay the interstitial spaces between clay and other mineral particles are filled with water. After the first firing (biscuit) the spaces are left empty. In this stage the clay body is porous. To test the porosity percentage, first weigh every strip then put them in boiling water for an hour. When it is done, take the strips out and weigh again. This is the formula :-

 dry weight – after boiling weight                                 100
_____________________________                     X         ____      =     percentage of porosity
             weight of dry                                                                       1

For example, the weight of my 1000℃ strip is 71g and after it has been boiled it is 81g, the difference is 10g. 10 multiplied by 100 = 1000 then 1000 divided by the weight of the dry strip is 71. The percentage of porosity of my 1000℃ strip is 14%.

Temp            After   firing                 After boiling          porosity percentage
1000℃          9cm        71g                       81g                            14%
1100℃          8.8cm     73g                       81g                            11%
1200℃          8.6cm     81g                       84g                             4%
The raw material after drying is 9.1cm
The 100g clay after drying has decreased to 80g , after firing has decreased to 74g

If clay contains lime it could cause the clay objects to break. When lime is fired it is altered from calcium carbonate to calcium oxide. Calcium oxide is an unstable oxide which takes on water or hydrates. This hydration will go on cause the lime swell and the swelling against the pressure of the clay objects during firing the piece will break.  A simple lime test can reveal whether lime is present in the clay. Roll a small ball of clay and skewer it on a tooth pick or bamboo stick then submerge it into 50% solution of hydrochloric acid. If lime is contained in the clay it will effervescence. My clay ball has bubbling a lot so it contains a large amount of lime.

Glaze test by using my dug clay

All glazes are a mixture of my dug clay, wood ash, whiting and feldspar, the proportion of which are shown in the following picture. Only the the wood ash (A) has the best result out of the other two. It is smooth and has a clear distinction between colours. The other two only have a subtle change.

test tile

 

hand building with Claire Cunreen

Coil building a vase. Claire showed us some pictures of vessels from different artists and we were asked to pick one of the artists’ works to build a vessel in which I chose Grayson Perry’s pot. I do like the surface decorating techniques he uses in his works, transfer printing, painting, sgrafitto, I guess he uses underglaze as well, they are all combined in one work. And I like he uses his works to pass messages or his emotion. I think I like his works in some degree.

https://florencefung.wordpress.com/2013/11/25/lost-in-words-in-constellation/

photo

 

Hand building with Matthew Thompson

Matthew Thompson  – technical demonstrator in clay and glaze, practicing designer and maker of ceramic tableware, plaster model and mouldmaking.  www.ceramicmatt.blogspot.co.uk

by Matthew Thompson

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In the lesson Matt demonstrated how to use slab roller machine and rolling pin to roll out clay slabs. Although the slab roller is more efficient and convenient, as a learner I prefer to everything put my hands on it to experience how materials are changed through the working process and to have better understanding of control materials. So most of my slabs were rolled out by rolling pin. Matt also showed us the slip join technique. Although I had experience of this technique from my evening class, it is good to have revision.

We were asked to build two small pots and a bigger vessel. I didn’t have any idea of what to build. I just randomly started to build a pot. This is the most interesting part of creation, now and then to let the materials lead you the way and tell how to move on. It was very funny that the pot was fairly similar to the calf I made in Natasha’s lesson. Based on its traits I continued to build another pot which was similar to the first one but with a twist.

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A larger slab-slip-join vase was also made. As the straightness of the vase could be warped due to its shrinkage in the drying process so I paid more attention to keep my vase drying evenly.

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Another hand building lesson with Matt. This time we concentrated on surface decorating/adding texture onto a ceramics surface. Colour slip, sgrafitto, inlay, grog..etc were introduced.

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First week activities – visit Cardiff Museum of Welsh

I love Lucie Rie’s works. She is an iconic potter of the twentieth century. The first time I saw her works was from a programme called “Ceramics the Fragile History” produced by BBC. Her works are combined with delicate, elegant, simplicity and modernism.

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Hans Coper

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Sorry, I am  just curious why the British love you so much, can you tell me why Toby?

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Other than good shapes and forms I also like surface decorating. It could be carving, slip decoration, sprigs decorations, painting or transfer printing.

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Soft-paste porcelain, Hard-paste porcelain. Would like to know more about these materials. So amazed that they could produce such a delicate little flowers

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These three vessels are smaller than the size of my palm. The colours and textures are so beautiful.

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