GB1604635A

GB1604635A - Production of decorative patterns on articles

Info

Publication number: GB1604635A
Application number: GB18098/77A
Authority: GB
Original assignee: Wedgewood & Sons Ltd Josiah
Current assignee: Wedgewood & Sons Ltd Josiah
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-12-09

Description

(54) IMPROVEMENTS IN AND RELATING TO THE PRODUCTION OF DECORATIVE PATTERNS ON ARTICLES (71) We, JOSIAH WEDGWOOD & BR< SONS LIMITED, a British company, of Barleston, Stoke-on-Trent, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to the production of decorative patterns on articles such as glassware, porcelain, pottery, china and metal products.

It is known to engrave a pattern on an article by applying a stencil carrying the pattern to a surface of the article and then subjecting the parts of that surface which are exposed through the stencil to a stream of abrasive particles. The stencil is prepared by cutting or stamping the pattern out of a sheet or foil, for example of paper.

However, it is difficult to produce fine or complicated patterns by this method because of the problems involved in cutting or stamping the stencil. There is also the problem that, particularly where the pattern involves fine tracery, it is difficult to ensure that the stencil is applied to the surface of the article without distortion.

According to the present invention, there is provided a method of producing a pattern on the surface of an article, the method comprising forming a latent stencil in the form of a foil having a protective coating medium applied to those areas of its surface other than those defining the pattern to be produced, bonding the latent stencil to the surface of the article, bombarding the latent stencil with a stream of abrasive particles whereby to remove by abrasion those areas of the latent stencil not coated with the protective coating medium and abrade the thus exposed areas of the surface of the article, and applying a surface coating material to the resultant pattern either before or after removing the remainder of the stencil from the surface of the article.

The surface coating material applied to the pattern may take various forms. For example the pattern may be pointed, enamelled (preferably with a vitreous enamel) or metallised. The coating may be applied while the foil is still bonded to the surface of the article using the foil as a stencil. Where the enamel requires subsequent firing, the foil may be destroyed during the firing thereby obviating the need for a further and separate step to remove the foil from the article.

The invention may be applied to the engraving of glass articles in which case the surface of the glass article is removed by abrasion to the desired depth in those areas of the latent stencil not coated with said protective coating medium.

The invention may also be applied to the application of decorative patterns to ceramic ware and especially, but not exclusively, to ceramic articles such as pots, jars, plates or tiles which have one or more engobe or slip layers applied to a surface thereof. An engobe or slip layer is a layer of coloured mineral composition, especially clay, which has been applied to the surface of the article to change its colour. Usually the engobe or slip is applied to the surface of the article before the latter has been finally fired, that is when the article is in the "green" or in the "biscuit" state, and is then hardened or vitrified during the process of firing the article.

In this case the engobe or slip layer is removed in certain preselected areas by the bombardment of the abrasive particles to expose the surface of the article underneath and thereby give a two-coloured pattern effect which is etched or engraved into the article.

Bold and pleasing effects can thereby be obtained.

The article may contain two or more engobe or slip layers of different colour and by using as many etchings or engraving steps as there are layers of engobe, a multicolour effect may be achieved. For example, in a first step using a first stencil, the bombardment may be sufficient to remove the top engobe or slip layer to expose the surface of the engobe or slip layer below it and in a second step using a second stencil (which may be formed by masking selected areas of the first stencil) the bombardment may be sufficient to remove parts of the thus exposed second engobe or slip layer, and so on with the last step removing selected parts of the lowermost engobe or slip layer and exposing the surface of the article.

Preferably the process is effected after firing of the engobe or slip layer or layers.

These layers are generally applied to the article when the article is in the unfired, that is the "green" state, and the etching process is therefore effected after the step of firing to vitrify or harden the article and its engobe or slip layer or layers. After the etching has been completed, a transparent overglaze can be added, if desired and the article subjected to a further firing in the normal way. Alternatively the process may be effected before firing of the engobe or slip layer or layers with the layer or layers dried to leather hardness.

Whether applied to glass, ceramic or other articles, the coated foil constitutes a latent stencil from which the stencil itself is produced after the foil has been bonded to the surface of the article and as part of the etching or engraving step. This latent stencil is dimensionally more stable than a conventional stencil and therefore is less liable to distortion in the process of applying it to the surface of the article As the coating can be applied by con ventional printing methods, such as silk screen printing, very fine and delicate patterns can be formed and these can be reproduced with excellent definition on the surface of the article.

The foil preferably comprises paper or plastics film. A thin metal foil, for example of lead or aluminium, may also be used, but this is less preferred, especially where the surface to be etched or engraved has a double curvature because metal foils are less easily applied to such surfaces. It is also preferred that the foil is a paper or plastics foil because it is more easy to ensure that the latent stencil obtained from it is adequately bonded to the surface of the article since the presence of undesirable air bubbles trapped between the latent stencil and the said surface can be more easily detected and since the foil will be more flexible.

So that it may be readily destroyed by the stream of abrasive particles, it is preferred that the foil is as thin as possible provided that it retains sufficient strength to be handlable with the coating on it without becoming distorted or damaged. Where the foil is paper, it will generally be between 0.0005 and 0.001 inch thick. Where plastics are used, even thinner foils may be used.

Examples of plastics foils are polyethylene, polypropylene and polyester film.

In the case of glass articles the foil is preferably black or a dark colour so that the disappearance of the unprotected areas under the action of the stream of abrasive particles can be readily observed.

The protective coating on the foil must be sufficiently thick that it is not penetrated by the stream of abrasive particles during the etching or engraving process. The desired thickness will therefore depend upon the nature and thickness of the foil, the abrasionresistance of the protective coating composition relative to that of the foil and the surface of the article, and the depth of etching or engraving desired in the surface of the article, and can readily be determined by simple experiment. As a general rule, however, the coating should be thicker than the foil, and is preferably at least 0.0005 inch and more preferably 0.00lO.004 inch thick, with thicknesses of 0.0015 to 0.003 inch being most preferred.Above about 0.005 inch, there tends to be loss in definition of the latent stencil due, for example, to creep of the coating medium but this may vary with the choice of medium.

While a coating medium in the form of an ink based on vinyl chloride polymer plastisol is preferred, any plastics-based ink may be employed provided that the print formed therefrom is suitably resistant to the stream of abrasive particles. Examples of other plastics-based inks that may be used include those based on butadiene copolymer emulsions, acrylic polymers and rubbers. In the case of glass articles the ink is preferably white or another colour which contrasts well with the colour of the foil.

While the pattern of coating medium may be formed on the substrate in any suitable manner, the much preferred method is by screen printing. The sharpness of the engraved image on the article will increase with the fineness of the screen and it is therefore preferred to use as fine a screen as possible provided it can be readily penetrated by the coating medium. I have found a 100 mesh screen to be generally suitable.

Preferred screens are formed of metal, for example stainless steel or metallised plastics.

Polyester screens may also be used although they are less satisfactory in that the image produced tends to be less well defined.

In order to obtain the necessarv thickness of coating without losing definition of the printed pattern on the foil, the ink or other coating medium, must be of relatively high viscosity. In general, its viscosity will be con siderably higher than the viscosity of normal printing inks and is preferably even higher than the viscosity of the plastics-based inks designed for printing on fabrics. By way of example, an ink of suitable viscosity may be obtained by adding about 3 ( to 8"; talc, by weight, to "Marlerfab" which is a com mercially available PVC plastisol-based ink for printing on fabrics.

In the preferred case where the ink is PVC plastisol-based, it is necessary to heat the ink imprint on the foil to cure the plastisol prior to subjecting the foil to abrasion.

Where screen printing is used, the pattern that is formed on the screen will be a positive of the pattern which is to be applied to the article; that is the areas of the screen which are rendered impermeable to the ink will correspond to the pattern which is to be engraved on the article. This positive may be produced in any suitable manner but preferably photographically. The corresponding negative pattern is then formed on the foil by applying ink to the foil through the thustreated screen in a well-known manner. The ink will pass through the screen in the areas which have not been rendered impermeable but will be prevented from passing through the screen in those areas which have been rendered impermeable.

The foil carrying the ink imprint outlining the pattern to be engraved on the article is applied to the surface to be engraved. While it is preferred to apply the foil with the inkcoated side facing away from the surface of the article, since this assists good bonding, this is not essential. However, it is important that the foil is bonded to the surface so that no movement of the foil relative to the surface and no lifting of the foil or any part thereof from the surface occurs during the etching or engraving of the article by abrasion. For example, merely clamping the foil to the surface is not sufficient. Although any suitable adhesive may be used to effect bonding it is preferably soluble in a solvent such as water so that the remains of the foil may readily be removed from the article by washing after completion of the abrasion process.

A suitable adhesive is gelatine.

In the case of ceramic articles to which the technique has been applied before firing the foil may advantageously be destroyed during the firing of the article thereby obviating the need for a further step to remove the foil.

An example of the invention applied to the engraving of a glass article is as follows: Example 1.

The pattern required to be engraved on an article was formed in ink impermeable material on a 100 mesh stainless steel "silk screen printing" screen by a conventional method.

An ink was prepared by adding about 3-S % by weight of talc to "Marlerfab" which is a printing ink containing a PVC plastisol base and which is sold by E. T. Marler of Deer Park Road, Wimbledon, London, England for printing on fabrics. The ink was then applied to tissue paper through the screen to form a negative of the pattern on the paper, that is a coating in which the ink was applied to those areas of the paper other than those defining the pattern to be engraved, thereby leaving the areas defining the pattern un coated. The thus formed ink coating was heated at 1300C for 30 seconds in order to gel the PVC.

The resulting latent stencil was applied to the surface of a brandy glass with the paper next to the glass, and bonded with a gelatine adhesive. Care was taken to en sure that the whole of that area of the latent stencil containing the pattern and the immediately surrounding areas were fully bonded to the glass with no air bubbles present.

After the gelatine had dried, the area of the glass covered by the latent stencil was bombarded by a stream of aluminium sili cate particles using a "MINIBLAST" dry blast machine as supplied by Abrasive Developments Limited of Henley-in-Arden, England. The bombardment was continued for a period sufficient to abrade away the uncoated paper and attack the thus exposed glass surface but such that the glass under those parts of the paper containing the ink deposit was untouched. An excellent image of the pattern was thereby formed in the glass with excellent definition of the fine detail.

An example of the invention applied to the decoration of a pottery article is as follows: Example 2.

A chequered pattern was formed in impermeable material on a 100 mesh stainless steel "silk screen printing" screen by a conventional method.

Employing this screen a negative of the desired pattern was printed on to tissue paper using an ink prepared in the same manner as the previous Example. The thus formed ink coating was heated at 1300C for 30 seconds in order to gel the PVC and provide a latent stencil.

A lidded box was made from white clay.

When the box and lid had dried to the correct consistency to avoid distortion a thin coating of blue clay slip (engobe) was applied to the outside surfaces of both parts (box base and lid) to a thickness of approximately imam. The box was then dried to biscuit state.

The latent stencil was then applied to the surface of the fired engobe-coated box lid and bonded to it with a gelatin adhesive.

Care was taken to ensure that the whole of that area of the latent stencil containing the pattern and the immediately surrounding areas were fully bonded to the box lid with no air bubbles showing.

After the gelatin had dried, the area of the engobe layer covered by the latent stencil was bombarded by a stream of aluminium silicate particles using a "MINI-BLAST" dry blast machine. The bombardment was con tinued for a period sufficient to abrade away the uncoated paper and remove the thus exposed engobe coating to expose the surface of the white biscuit underneath it, but such that the engobe layer under those parts of the paper containing the ink deposit was untouched. An attractive blue and white chequered pattern was obtained. Any remnants of the latent stencil were then removed prior to firing by rubbing or washing with water.

A further example of the invention am plied to the decoration of a pottery article is as follows: Example 3.

A chequered pattern was formed in impermeable material on a 100 mesh stainless steel "silk screen printing" screen by a con ventional method. Employing this screen, a negative of the desired pattern was printed on to tissue paper using an ink prepared in the same manner as the previous Example.

The thus formed ink coating was heated at 1300C for 30 seconds in order to gel the PVC and provide a latent stencil.

A black tile 6" X 6" was made from a red clay with added manganese oxide and cobalt oxide. The tile was allowed to dry and when it could be handled without the risk of distortion the tile was dipped into a white engobe to form a coating thickness of lmm after drying. This coating was allowed to dry to leather hardness.

The latent stencil was then applied to the surface of the engobe-coated tile and bonded to it with a gelatine adhesive. Care was taken to ensure that the whole of that area of the latent stencil containing the pattern and the immediately surrounding areas were fully bonded to the tile with no air bubbles showing.

After the gelatine had dried, the area of the engobe layer covered by the latent stencil was bombarded by a stream of aluminium silicate particles using a "MINI BLAST" dry blast machine. The bombardment was continued for a period sufficient to abrade away the uncoated paper and remove the thus exposed engobe coating to expose the surface of the black tile underneath it but such that the engobe layer under those parts of the paper containing the ink deposit was untouched. An attractive black and white chequered pattern was obtained.

The tile was then fired in conventional manner at about 10000C and the remnants of the latent stencil were destroyed during the firing. Alternatively, these remnants could have been removed prior to firing, for example by washing with water.

In the case of all the above examples the resultant pattern may be painted, enamelled or metallised either before or after removal of the foil from the surface of the article.

Where the article requires subsequent firing the foil may be destroyed during firing.

Various modifications may be made without departing from the invention. For example protective coating mediums other than ink may be used and the invention may be applied to the decoration of other articles, for example metal products. In relation to the decoration of ceramic articles the invention may be applied at any stage during production, that is in the unfired clay or "green" state, in the biscuit state or in the glazed or enamelled fired state. It is also applicable to articles which are not provided with engobe or slip layers.

WHAT WE CLATM IS: 1. A method of producing a pattern on the surface of an article, the method com.

prising forming a latent stencil in the form of a foil having a protective coating medium applied to those areas of its surface other than those defining the pattern to be produced, bonding the latent stencil to the surface of the article, bombarding the latent stencil with a stream of abrasive particles whereby to remove by abrasion those areas of the latent stencil not coated with the protective coating medium and abrade the thus exposed areas of the surface of the article, and applying a surface coating material to the resultant pattern either before or after removing the remainder of the stencil from the surface of the article.

2. A method according to claim 1 wherein said article is a glass article the surface of which is removed by abrasion to the desired depth in those areas of the latent stencil not coated with said protective coating medium.

3. A method according to claim 1 wherein said article is a ceramic article having an engobe or slip layer applied to a surface thereof, the engobe or slip layer being removed by abrasion to expose the surface of the article underneath and thereby produce a two-coloured pattern effect.

4. A method according to claim 3 wherein the article is provided with a plurality of engobe or slip layers of different colour, a plurality of etching or engraving steps being applied to successive layers to produce a multi-colour effect.

5. A method according to claim 4 wherein the number of etching or engraving steps corresponds to the number of layers whereby to expose a portion of the surface of the article after the final step.

6. A method according to any of claims 3 to 5 wherein the abrasive bombardment is effected after firing of the engobe or slip layers.

7. A method according to any of claims 3 to 5 wherein the abrasive bombardment is effected after drying of said layer or layers to leather hardness but before firing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tinued for a period sufficient to abrade away the uncoated paper and remove the thus exposed engobe coating to expose the surface of the white biscuit underneath it, but such that the engobe layer under those parts of the paper containing the ink deposit was untouched. An attractive blue and white chequered pattern was obtained. Any remnants of the latent stencil were then removed prior to firing by rubbing or washing with water. A further example of the invention am plied to the decoration of a pottery article is as follows: Example 3. A chequered pattern was formed in impermeable material on a 100 mesh stainless steel "silk screen printing" screen by a con ventional method. Employing this screen, a negative of the desired pattern was printed on to tissue paper using an ink prepared in the same manner as the previous Example. The thus formed ink coating was heated at 1300C for 30 seconds in order to gel the PVC and provide a latent stencil. A black tile 6" X 6" was made from a red clay with added manganese oxide and cobalt oxide. The tile was allowed to dry and when it could be handled without the risk of distortion the tile was dipped into a white engobe to form a coating thickness of lmm after drying. This coating was allowed to dry to leather hardness. The latent stencil was then applied to the surface of the engobe-coated tile and bonded to it with a gelatine adhesive. Care was taken to ensure that the whole of that area of the latent stencil containing the pattern and the immediately surrounding areas were fully bonded to the tile with no air bubbles showing. After the gelatine had dried, the area of the engobe layer covered by the latent stencil was bombarded by a stream of aluminium silicate particles using a "MINI BLAST" dry blast machine. The bombardment was continued for a period sufficient to abrade away the uncoated paper and remove the thus exposed engobe coating to expose the surface of the black tile underneath it but such that the engobe layer under those parts of the paper containing the ink deposit was untouched. An attractive black and white chequered pattern was obtained. The tile was then fired in conventional manner at about 10000C and the remnants of the latent stencil were destroyed during the firing. Alternatively, these remnants could have been removed prior to firing, for example by washing with water. In the case of all the above examples the resultant pattern may be painted, enamelled or metallised either before or after removal of the foil from the surface of the article. Where the article requires subsequent firing the foil may be destroyed during firing. Various modifications may be made without departing from the invention. For example protective coating mediums other than ink may be used and the invention may be applied to the decoration of other articles, for example metal products. In relation to the decoration of ceramic articles the invention may be applied at any stage during production, that is in the unfired clay or "green" state, in the biscuit state or in the glazed or enamelled fired state. It is also applicable to articles which are not provided with engobe or slip layers. WHAT WE CLATM IS:

1. A method of producing a pattern on the surface of an article, the method com.

8. A method according to claim 7 wherein

the article is subsequently fired.

9. A method according to any of daims 3 to 5 or 8 wherein the article is glazed before or after firing.

10. A method according to any preceding daim wherein said protective coating medium is a plastics-based ink medium.

11. A method according to claim 10 wherein said ink medium is a PVC plastisol.

12. A method according to claim 11 wherein said ink medium is heated after application to said foil to cure the plastisol.

13. A method according to any preceding claim wherein said protective coating medium has a high viscosity.

14. A method according to claim 11 or 12 and claim 13 wherein said plastisol incorporates from 3% to 8% talc by weight.

15. A method according to any preceding claim wherein the thickness of said coating medium is between 0.0005 and 0.005 inch.

16. A method according to any preceding claim wherein said protective coating is ap plied by screen printing.

17. A method according to claim 16 wherein the printing screen is formed of metal or metallised plastics material.

18. A method according to any preceding claim wherein said foil is applied to the article with the coated side facing away from the surface of the article.

19. A method according to any preceding claim wherein said foil is selected from paper, plastics film and metal foil.

20. A method according to claim 19 wherein said foil comprises polyethylene, polypropylene or polyester film.

21. A method according to any preceding claim applied to a glass article wherein said foil is dark in colour.

22. A method according to claim 21 wherein said protective coating medium is light in colour.

23. A method according to any preceding claim wherein said foil is bonded to the surface of the article by an adhesive.

24. A method according to claim 23 wherein said adhesive is water soluble.

25. A method according to claim 24 wherein said adhesive is gelatin.

26. A method according to any preceding claim wherein the surface coating material applied to the resultant pattern is applied before removal of the foil from the surface of the article, using the foil as a stencil.

27. A method according to claim 26 wherein the article is subsequently fired to harden said surface coating material and burn off the remainder of the stencil.

28. A method of producing a pattern on the surface of an article substantially as wherein before described.

29. An engraved article produced by the method according to any preceding claims.