GB2235189A - Ceramics - Google Patents

Abstract

A mat of glass fibres is coated in a ceramic slip or slurry and then dried. The resulting material may be moulded and fired to form a porcelain product, or two sections of the material may be formed into a laminate, which is fired. In the fired products the glass fibres disappear by melting and patterns or figures may be provided in the product by using appropriate formations of the glass fibre mat.

Description

IMPROVEMENTS IN OR RELATING TO CERAMICS This invention concerns improvements in or relating to ceramics.

It is particularly concerned with a technique for strengthening ceramic material to enable it to be worked and shaped into ceramic ware particularly where very thin walled sections are used to provide fine porcelain since in such cases working the material can be extremely difficult as the thickness of the material is reduced.

It has been proposed to reinforce clay products, e.g. sculptures, by adding fibrous cloths to the surface. It has also been proposed to increase the strength of clay by adding chopped fibres.

According to one aspect of the present invention there is provided a method of forming a ceramic product comprising providing a mat or felt of glass fibre, coating the mat in a ceramic slip or slurry and drying to a workable state, then cutting, moulding or otherwise forming the sheet into a ceramic product.

The present invention provides very thin section ceramic material which is workable because the glass fibre mat provides strength in the unfired product.

Preferably, the mat or felt is dipped into the ceramic slip whereby the slip coats the glass fibre mat. Preferably the method comprises drawing the glass fibre mat through a vat of ceramic slip whereby the slip attaches to and coats the mat and thereafter drying the coated mat.

By selecting the density of the mat, selecting the solids content of the slip and by adjusting the speed with which the glass fibre mat is drawn through the slip, it is possible to adjust the weight of slip which attaches to and coats the mat thereby altering the thickness of the material so formed. The mat may be of a density of the order of loz per sq yd and of the order of 3rtrn thick. The slip may be of the order of 35% water content and materials of varying density can be formed by adjusting the amount of slip deposited on and coating the mat.

The material so formed may be used to mould or work into ceramic ware. Alternatively, two or more sections of such material can be pressed together to form laminate which can then be worked or formed to form ceramic ware. The different sections of material pressed to form a laminate may be of different colours or of different configurations, may have different structures or appearances or may provide other differing characteristics for the finished ware.

According to another aspect of the present invention a method of forming decorated porcelain comprises forming a sheet from a felt of glass fibres coated with porcelain slip, decorating a surface of the sheet with coloured felt of glass fibre coated with porcelain slip and firing the decorated sheet whereby the glass fibres melt into the porcelain leaving decorated ceramic.

According to a further aspect of the present invention a method of forming decorated porcelain comprises forming a sheet fran a felt of glass fibre coated with porcelain slip, decorating a surface of the sheet, laminating to the decorated surface a second sheet made from a felt of glass fibres coated with porcelain slip, and firing the laminate to form a translucent ceramic through which the decoration can be viewed.

Preferably the decoration is formed frcm a coloured sheet or sheets of glass fibre felt coated with porcelain slip, cut to shape and applied to the surface.

The fibres may be in the form of a mat or felt, and the sheets may be formed by drawing the glass fibre felt through a porcelain slip and drying the sheets until touch dry and workable.

The sheets are preferably cut and formed to produce a vessel or article of porcelain.

According to another aspect of the present invention there is provided decorated porcelain formed by any of the methods set forth above.

After forming or working the material it is fired to provide the finished ceramic ware. The action of firing the ceramic material with the glass fibre embedded therein can cause the glass fibre to melt and mix with the ceramic material whereby the material becanes completely translucent and the presence of the glass fibre is not detectable. However, at this time the ceramic material will have dried sufficiently for it to be self supporting and the strengthening provided by the glass fibre during the drying, forming and working processes will have been utilised and thereafter no longer required.

The invention will now be described with reference to an example.

To form a square receptacle of translucent porcelain, a vat or vessel is filled with a low firing porcelain slip as made by Valentines of Stoke-on-Trent, having 35% moisture content and including deflocculents.

A glass fibre felt typically surfacing tissue supplied by Glasplies of Southport having a weight of loz per sq yd and being 3mm thick is cut to a size 21cm by 21cm and is immersed in the slip until the slip permeates through the fibres and is drawn through the slip at such a speed that the slip coats the felt and forms a thin walled ceramic sheet in which the glass fibre is completely embedded within the ceramic slip.

The wet sheet is placed on a plaster table and allowed to dry until it is sufficiently dry to permit working of the material.

The material is worked by cutting 52cm square portions fran each corner of the rectangular sheet thereby leaving a cruciform shape.

The 52cm protrusions are folded at 90" to the 10cm square base to form a tray or receptacle 10cm square and 52cm high. The corners are sealed using ceramic slip to form a sealed receptacle.

The formed sheet is allowed to dry further and is then fired at approximately 12000c during which process the glass fibres melt and are absorbed within the ceramic material leaving a completely translucent vessel.

By using the glass fibre reinforced ceramic sheet, material as thin as 3rtrn can be worked to provide extremely thin walled wares and providing thicknesses which could not be worked without the reinforcement without great difficulty. Glass fibre felts as thin as l2irEnt could be used, having a density of -21oz per sq yd to form thin walled wares.

In a modified technique, d number of sheets of ceramic material produced by drawing glass fibre mats through ceramic slips are pressed together before they are dry, thereby forming a laminate of the sheets of materials. In this way, thicker wall sections can be built up. In all instances, the subsequent firing of the material which has been formed and worked into the desired shape will cause the glass fibre to disappear by melting into the ceramic material thereby leaving a completely clear and translucent material.

The technique can be used to laminate sheets which are of different appearances or different materials thereby forming patterns or structures not otherwise available. The ceramic slips could for example be coloured differently.

Typically, two sheets of material are made and cut to cruciform shape in the manner set forth above. One of the sheets is decorated and the decorated surface is then covered with the second sheet of material to form a laminate in which the decorated surface is within the material.

Preferably the decoration is achieved by using sections cut fran a glass fibre sheet coated in ceramic slip in the manner described above, the fibre and/or slip being coloured. A number of such sheets may be used if a number of colours is required. Any size and shape of design can be cut from these sheets and applied to the surface to be decorated.

The laminated material with the decorated surface sandwiched between sheets of material is fired at 12000c. The firing causes the fibres to melt and fuse into the ceramic material. After firing the fibres are not noticeable but the colouring is disposed within and forms a pattern within the translucent porcelain which can be observed by looking through the thin walled material.

It will be appreciated that the ceramic material formed by this invention can be worked into any shape and by any suitable technique available to ceramic workers and vessels of any thickness can be produced.

The density of the glass fibre matting used can vary according to the needs of the material. Felts from 2 to loz per sq yd and fran 121 to 3mm thick can be used. The consistency of the slip can be altered according to the thickness of the vessel wall which it is desired to form and the speed at which the fibre is drawn through the vat of ceramic slip can be adjusted to vary the thickness of the sheet manufactured.

If it is decided not to work the ceramic sheet in the usual drying period after formation, it is possible to delay that drying period by, for example, enclosing the sheet within film or other impermeable material which delays drying of the material.

By forming a pattern on the glass fibre mat coated with ceramic slip, it is possible to form designs within the ceramic ware which are left by the melting glass fibre during firing whereby 'watermark' type appearances can be given to the ceramic ware.

The appearance of letters, figures and devices can be formed in the walls of the ceramic ware in this way.

The materials may be glazed or burnished using known techniques. By the present invention there is provided a technique for providing thin walled ceramic material which can be formed and worked to form translucent ware in much thinner thickness than would otherwise be available due to the presence of the glass fibre reinforcement. There is also provided a technique for providing patterns or figures within the walls of the translucent ware by appropriate formation of the glass fibre matting.

The material can be formed, turned, moulded into any size and shape vessel or article or can of course be pressed and rolled to form sheets which could form decorative articles, e.g. window panes or decorative translucent panes.

Claims (11)

1. A method of forming a ceramic material comprising providing a mat or felt of glass fibre, coating the mat in a ceramic slip or slurry and drying.

2. A method as claimed in claim 1 comprising dipping the mat or felt into the ceramic slip or slurry whereby the slip coats the glass fibre mat.

3. A method as claimed in claim 2 comprising providing a vat of ceramic slip, drawing a glass fibre mat through the slip whereby the slip attaches to and coats the mat, and drying the coated mat.

4. A method as claimed in any preceding claim wherein the mat is of the order of 0.5 to loz/yd2 and the slip has a consistency of 35% water.

5. A method as claimed in any preceding claim comprising pressing two or more sections of such material together to form a laminate.

6. A method as claimed in any preceding claim comprising forming or moulding the material and subsequent firing the material.

7. A ceramic material comprising a mat or felt of glass fibres coated with ceramic slip.

8. A ceramic material comprising a mat or felt of glass fibre embedded within a ceramic slip.

9. A ceramic material comprising a mat or felt of glass fibres of density 0.5 to loz/yd2 embedded within a ceramic slip.

10. Ceramic ware comprising ceramic material according to any of claims 7 to 9.

11. Ceramic ware comprising ceramic material formed by the method of any of claims 1 to 6.