Making a Blue Bottle

There are a few steps necessary to making this particular ceramic object. We shall look at them one by one.

Making a Model
The first step is to make a model of the bottle we want to make. The model should be about 12% larger than the finished product you would like to have, because, as most of you will know, clay shrinks on drying and on firing. The slip we are going to use for this project will shrink about 12%. Make the model out of clay by cutting out  a cardboard template for the shape you want to get. This should be a profile, that you can hold up against the model, to see if it has the right shape. Make sure there are no 'undercuts'. Make the model on the potter's wheel, by either throwing it solid, or by coil building or a combination of both. Use any other method if you have one, e.g. you might just find a large glass bottle that you like, and cast the shape from that. Of course then, you will save yourself the work of making the model in clay, but you will still have to fill in any undercuts with clay (typically the bottom of the bottle).

Making a Two Piece Mold
Once you have your model, make sure it's top opening is closed. If you are using a glass bottle, plug up the top with a ball of clay. Now you are ready to proceed to the next step, which is making your plaster mold. Make a form out of wooden boards, that will comfortably hold your bottle form, and still have about 1 - 11/2 inches (2.5 - 4 cms) space left over. Embed the bottle form half way up in clay, so that you can pour the top half in plaster. Let the top touch one of the walls, when you do this. That will become the opening in which you will pour the slip, once it is all finished. If you are unfamiliar with this technique, please refer to Making a Plaster Mold for more information. When the plaster has hardened (usually it's best to wait overnight), turn the mold around and clear out the clay, that was holding your model, being careful not to damage the model's surface in the process. Every little scratch will show up in the finished mold. Once the clay is removed (it should peel off from the plaster easily enough), you should coat the plaster with several layers of soft soap. Brush this on with a flat brush. Work up a lather and then wipe the surface with a cloth. Do this several times -- the more the better. The plaster should be impregnated with the soap, but don't use soap concentrate, as this could weaken the plaster. Doing this will stop the second layer from sticking to the first, so you can separate the two halves. Don't be too eager to open the mold, it dry out for a couple of days -- this will give the plaster enough time to harden properly. Now you should be ready to separate the two halves, by gently tapping the mold's side with a rubber mallet. Using your hands, pry the two halves apart. If they don't come apart easily, you may need to use a little more force: hammer in a chisel between the two halves, at the seam. Do this on all three sides (not where the opening is), but do it carefully! Once the mold is open, let you model shrink a bit -- it should pop out easily.

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