Sound Extrusions: Porcelain Reloaded

Plaster molds for the porcelain speakers


Plaster molds for the porcelain speakers
Plaster molds for the porcelain speakers

The “hero shot” in this post (above) is a picture of clay models of the porcelain shapes. They were used to create actual plaster moulds. This is one of the first steps towards the final porcelain speaker shells  the main features of the project. The idea behind creating a porcelain object is very straight forward: once we finish a model in clay, we are ready to cast a plaster mould and use it as a negative shape for later porcelain slip casting. This is the most common approach. The beauty of plaster mould is in the fact that we can replicate the objects many times afterwards (3D printing is also pretty good in that regard, as we saw in the last post!), and that we are able to refine our object to finer detail while editing the plaster mould too. But the biggest advantage compared to a direct modelling approach, is the far greater chance of fault free product in the end, thanks to the process of slip casting.

The intriguing story of the Meissen porcelain manufacture workshop, from the beginning of 18th Century, was covered in one of the previous posts. It gave us an unusual introduction to this exciting material. But let’s leave the mystery of European manufacturing behind us for now, and let’s have a look at the process of porcelain making itself!

Making plaster moulds is in fact an art in itself. The reason for this claim is that complicated shapes require plaster moulds to be “assembled” out of many interlocking pieces. The reason for that is that you have to be able to take the mould apart once the object is casted. The only way to achieve this is to divide the clay model into virtual plains and cast the mould step by step, creating separate interlocking pieces as you go. Even some of the finest porcelain makers and designers leave this process to experienced mould makers.

Another step in the production is the magic of porcelain slip casting — in fact it’s fairly simple, but you wouldn’t know unless you knew what to ask for! By pouring liquid porcelain into the plaster mould we create the porcelain slip. But the real secret is in the plaster itself — more specifically, in the porosity of the material. Plaster in fact, is made of a maze of little tunnels and microscopic cavities, which are ready to absorb water. And here the magic starts. By pouring the liquid porcelain into plaster mould, the water in the porcelain gets absorbed into plaster and we are left with thin sediment crust. (Yes, this is already your favorite translucent coffee cup with a dragon!) After a few minutes we are left with a few millimetres thickness of porcelain wall. The rest of the liquid is poured away and the casted slip starts to shrink and pops easily out of the mould.

Sounds simple, but we are not done yet! The secrets of kiln and glaze firing are the most intriguing and guarded secrets. Porcelain firing temperatures reach up to 1280C, while the whole process is divided into two steps — the bisque firing (makes the whole object hard and reveals any material impurities like micro-cracks — oh no!) and the final glaze firing, which gives the porcelain body the glass like qualities and creates the sleek look of the porcelain objects.

In such a short introduction to the material, there was already lots of information. But let’s have a look, for a change, at how the old fashion decorative porcelain concept turns into a challenging adventure in contemporary design!

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There’s one more “detail” to porcelain production. While watching a short documentary on Bugatti Veyron L’Or Blanc and the use of unusual porcelain interior decorations, be aware, that porcelain shrinks by 14-16% throughout the whole production. In other words, matching precisely crafted interior car parts with porcelain custom shapes must have been an adventure of its own!

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