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Friday, 23 September 2011

Willow strikes a pose

I have just spent the last few days with little Willow, a tiny Manchester terrier, who came to have her portrait sculpted in clay, for a bronze.

Here are some pictures of Willow and the sculpture in clay. I'll post another picture of the bronze and of the casting process when ready.

Ok so here are the steps of the casting process:

Ingredients needed:
Runny silicon and catalyst (Find at Tiranti on warren street)
Putty Silicon and catalyst (Tiranti)
Casting plaster (Find at Travis Perkins- get the same plaster you use for cornicing)
Casting wax (Tiranti)

Step 1: Make a tray out of clay to catch any drips.

Step 2: Mix the runny silicon with the correct amount of catalyst and pour over the clay starting from the highest point.

  Step 3: Blow on the silicon to make sure it has entered into all the nooks and crannies. Leave to dry over night.
Step 4: Repeat step one and two and leave to dry again. Then remove any drips once hard with a knife.

Step 5: Take the putty Silicon and mix with the catalyst. Then using your hands push small pieces about 1 ½ cm thick all over the form.
Step 6: Decide where your seam will be, you must be careful when you choose this that you do not have any undercuts. I.e. you must be able to remove the silicon and plaster mould without breaking any of the cast form. Then using the putty silicon make a wall around where you have chosen the seam.

Step 7: Make a clay wall around the seam.
Step 8: Mix your plaster in a clean bowl. First pour the water then gently spoon the plaster on top. Do not mix until you have added enough plaster that it forms a peak in the water. Once you mix you can no add any more plaster or you will get air bubbles in the form.

Step 9: Sprinkle some of the runny plaster onto one side of the mould then wait for the rest to start to harden before pasting on the rest creating a wall around the silicon of about 2 inches.
Step 10: Remove the clay wall and before it has hardened using a tsp carve out some keys into the plaster so that the two sides can lock into each other. Smooth down the mould all over so you are not left with spiky bits.

Step 11: Glaze the inside of the plaster wall with some clay slip or Vaseline. This is so you can part the mould easily.

Step 12:  Repeat the process on the other side

Step 13: When you have the complete mould you need to crack it open using a flat-headed chizzle. The sides should part easily to uncover the silicon.
Step 14: With a Stanley knife cut through the middle of the seam and open the silicon.
Step 15: Remove the clay and clean the silicon mould under the tap so it is spotless.
Step 16: you now have a silicon mould that you can use to cast a wax version of the sculpture that you can then use for bronzing and the lost wax technique. You can also use this mould for casting in resin and plaster.

Tuesday, 6 September 2011

Camping at Punta Alla

Last weekend I went camping with friends from Florence, at a place called Punta Alla on the Tuscan coast.  We set up in our usual spot, looking out over Elba, in the pine wood that lines the edge of the beach. We tied up our hammocks, so that you can see the sea, but remain comfortably shaded by the tall and decorative trees, that threaten you with their precarious pine cones, jutting out from every branch. Here are some of the paintings I made from our camp.

Photos by Giuseppe Citino

Thursday, 1 September 2011

My Sculpture and the lost wax technique

I have just come back from Siena where I was sculpting a portrait in clay, which I am taking to the foundry, tomorrow to be cast in bronze. Here is a picture of the clay and the lady you sat for me, Dominique S-J.

To make a bronze, using the lost wax process, is quite a complicated practice. Firstly a mould has to be made from the original, in silicon from which you can cast a hollow wax copy. Next one works on and re-touches the wax. In the case of this sculpture I will be paying particular attention to fixing the neck of the piece, as you can see the armature has got in the way, but this can all be corrected at the wax stage.
Once the wax has been corrected and signed by the artist you hand it back to the foundry where the lost wax process can begin.
 Each hollow wax copy is then "chased": a heated metal tool is used to rub out the marks that show the parting line where the pieces of the mold came together. The wax is dressed to hide any imperfections. The wax now looks like the finished piece. Wax pieces that were molded separately can be heated and attached; foundries often use registration marks to indicate exactly where they go.
 The wax copy is then sprued or gated with a treelike structure of wax that will eventually provide paths for molten casting material to flow and air to escape. The carefully planned spruing usually begins at the top with a wax "cup," which is attached by wax cylinders to various points on the wax copy. This spruing doesn't have to be hollow, as it will be melted out later in the process. A sprued wax copy is then dipped into a slurry of silica, then into a sand-like stucco, or dry crystalline silica of a controlled grain size. The slurry and grit combination is called ceramic shell mold material, although it is not literally made of ceramic. This shell is allowed to dry, and the process is repeated until at least a half-inch coating covers the entire piece. The bigger the piece, the thicker the shell needs to be. Only the inside of the cup is not coated, and the cup's flat top serves as the base upon which the piece stands during this process. The ceramic shell-coated piece is placed cup-down in a kiln, whose heat hardens the silica coatings into a shell, and the wax melts and runs out. The melted wax can be recovered and reused, although often it is simply burned up. Now all that remains of the original artwork is the negative space, formerly occupied by the wax, inside the hardened ceramic shell. The feeder and vent tubes and cup are also hollow. The ceramic shell is allowed to cool, then is tested to see if water will flow through the feeder and vent tubes as necessary. Cracks or leaks can be patched with thick refractory paste. To test the thickness, holes can be drilled into the shell, then patched. The shell is reheated in the kiln to harden the patches and remove all traces of moisture, then placed cup-upwards into a tub filled with sand. Metal is melted in a crucible in a furnace, then poured carefully into the shell. If the shell were not hot, the temperature difference would shatter it. The filled shells are allowed to cool. The shell is hammered or sand-blasted away, releasing the rough casting. The sprues, which are also faithfully recreated in metal, are cut off, to be re-used in another casting. Just as the wax copies were chased, the casting is worked until the telltale signs of the casting process are removed, and the casting now looks like the original model. Pits left by air bubbles in the casting, and the stubs of spruing are filed down and polished. Then to change the colour of the bronze, to your preferred patina the cast is heated with an open flame until scolding hot and various chemicals are applied, which react with the metal and change the colour accordingly.