This invention relates to methods of casting and reproduction of water-containing materials and in particu¬ lar, but not exclusively, to casting of clay bodies such as 5 porcelain, bone china, redware, stoneware etc.

There are a variety of ways in which fine "artware" may be produced. It is known to cast resin mixes in finely detailed silicone rubber moulds to produce articles with correspondingly fine detail. To produce such articles from 10. porcelain or china it has been necessary to use multipart rigid moulds to cast different parts of the article which are then assembled and finished by a skilled craftsman and this has made production complicated, time-consuming and costly. Moreover the multipart moulding techniques cannot 15 cope with designs incorporating many undercut features.

As a result the articles produced by the multipart moulding techniques can look flat and lifeless compared to their resin cast counterparts or one-off original designs.

Although the resin casting technique allows finely 0 detailed articles to be cast in resin, ceramic articles are still preferred and seen as being of premium quality and are - of food grade.

A need thus exists for a method which allows ceramic and other materials to be cast in quantity to produce finely - 5 detailed articles, without using multipart moulds.

Accordingly, in one aspect, there is provided a method of casting an article from a water-containing material which comprises the steps of:-

(a) introducing a charge of said water-containing material into a mould of flexible or resiliently distortable material;

(b) exposing said mould and the material therein to a reduced temperature at least partially to freeze said material;

. (c) removing said material from said mould whilst at least partially frozen, and

(d) causing or allowing said material to dry, harden or set after removal from said mould.

Preferably, said method also includes the step of causing or allowing removal or separation of an amount of water from the charge in the mould before the mould is exposed to said reduced temperature. The removal or separation may be achieved in a variety of ways. The mould and its contents may be centrifuged to cause an amount of water to separate from the remainder of the material, thus forming a supernatant layer.

Alternatively, the mould and its contents may be left for a while to cause water to separate from the remainder of the material.as a consequence of natural settlement. This natural settlement may be accelerated by vibrating the mould and its contents, for example on a vibrating table.

Yet further, the mould and its contents may be left to allow water loss by evaporation until the mould contents reach a semi-dry condition. This may be accelerated by heating until the surface of the contents is semi-dry. The water-containing material is preferably a ceramic and the

part-formed or "green-formed" article is preferably fired following removal from the mould and drying. The water- containing ceramic material may comprise a clay body such as porcelain or bone china, etc. The formulation of the clay body, including the particle sizes and the various proportions of the constitu¬ ents may be adjusted as required to give a suitable pouring consistency without leaving voids in the mould. Depending on the particular method to be employed, the clay body may include a flocculant, for example aluminium sulphate, to assist settling-out of the clay body.

In alternative techniques according to the invention, the clay body may be semi-solid or solid and pressed into the mould instead of being poured into it. The water-containing material is preferably degassed prior to pouring into the mould, for example, by placing in an atmosphere at reduced pressure, e.g. in a vacuum tank.

The supernatant water (where present) is preferably removed from the mould prior to the freezing step. Where the article to be moulded is bulky, it may be hollow cast by introducing into the mould a plug or core around which the water-containing material passes. In some arrangements, the plug or core may be a reduced size replica of the original article, which may be produced by the miniaturisation process defined below.

There is often a requirement to reproduce articles on a different scale, for example, when making sets of jewel¬ lery etc. I have found that when the above technique is

applied to casting ceramic materials there is a net shrink¬ age of the finished article typically of between 10% and 12% (though this may vary with the selection of suitable materials) . Accordingly, in another aspect of this invention, there is provided a method of reproducing an article on a reduced scale, which comprises the steps of:-

(a) forming a complementary mould of flexible or resiliently distortable material around an original article; (b) removing said original article, leaving a formed mould;

(c) introducing a charge of water-containing material into the formed mould;

(d) exposing said mould and the material therein to. a reduced temperature at least partially to freeze said material;

(e) removing said material from said mould whilst still at least partially frozen, and

(f) causing or allowing said material to harden or set and shrink after removal from said mould thereby to form a reduced size copy of said original article.

The above technique allows articles to be reproduced on a reduced scale whilst maintaining a high definition of detail. The method preferably includes the step of causing or allowing removal of an amount of water from said charge in said mould before said mould is exposed to said reduced temperature.

The hardening or setting is preferably achieved by firing the material.

The term "original" is used to identify the article to be copied, and is not intended to exclude the possibility that the article is itself a copy.

The reduced size copy produced in step (f) may itself be used as an original in a subsequent process in which steps (a) to (f) are repeated as necessary to produce successive reductions in size. The reverse of the above technique may be applicable in some circumstances. In such a preferred process, a water- containing material is formed around an original article of flexible material, an amount of water is then separated from said water-containing material, the remaining water- containing material is then frozen, the flexible original is removed, and the water-containing material caused to harden or set and shrink thus producing a reduced size three-dimen¬ sional "negative" of a flexible original "positive".

Example 1 A series of silicone rubber moulds was prepared by carving original pieces and placing them in separate mould boxes into which was poured a silicone rubber and catalyst. Once the silicone rubber had cured, the original pieces were removed leaving the moulds ready for use. A porcelain slip was selected with a "runny" consistency which could be poμred freely into the mould and be de-gassed relatively

easily. A suitable slip is "White Orchid Porcelain Slip" available from Bell Ceramics, Clermont, Florida, U.S.A., although many other materials may be formulated and used.

The slip was placed into a vacuum tank of the type used for de-gassing resins in resin casting processes for about 15 minutes to de-air it. The slip was. poured into the moulds and _. the moulds then returned to the vacuum tank for about 10 to 15 minutes. The moulds were then placed into a centrifuge having a mean radius of about 0.75m and operating at between 40 and 80 rpm, for half an hour so that the constituent particles of the porcelain slip separated out from the excess water, with the majority of the water lying on the surface as supernatant fluid.

The moulds were removed from the centrifuge and the supernatant fluid poured off. The moulds were then placed into a freezer at temperature of about -10°C for between 1 and 2 hours until the mix was frozen. The frozen pieces were removed from the moulds and left for about 2 days to dry completely, ready to be fired. The dry pieces were fired in a kiln in the normal way. The finished pieces were typically 10% to 12% smaller than the original piece.

Example 2 The series of moulds of Example 1 were filled with de- aired porcelain mix and de-aired as previously and then left to dry for a period of a few days, depending on the volume of the moulds, until the top surface of the contents was semi-dry. The moulds were frozen, the frozen pieces were

removed and allowed to dry before being fired as previously to produce the finished pieces.

The above techniques allow extremely complicated pieces to be cast in a single mould. . 5 Also, the techniques allow a design to be made smaller and this may be repeated as necessary progressively to reduce a design to a required size. Thus one of the finished pieces in the above example could be used as an "original" to produce a further silicone mould of reduced 10. size compared to the original mould which then produces a finished piece of further reduced size and so on.