FIELD OF INVENTION
This invention relates to a process of cladding silver and other non ferrous metals such as copper, nickel, lead and their alloys on non¬conducting surfaces, more specifically on glassware and ceramics.
BACKGROUND OF THE INVENTION
Both for utility and aesthetic purposes, a combination of Glassware/ceramic products with silver or other nonferrous metals such as Copper etc. has been attempted for centuries. However very limited success has been achieved as intricate patterns of silver/nonferrous metals are extremely difficult to fix or permanently glue onto glass/ceramics. A very high level of skill and intensive labour is required in manually cladding silver or nonferrous metals onto non-conducting surface like glass, ceramic, pottery and stoneware, thus making the whole process commercially unviable.
Conventional Technique of Silver Cladding along with Drawbacks
There are many conventional methods by means of which silver or other non-ferrous metals cladding is done on various non-conducting surface like glass, ceramic, pottery and stoneware. The process of silver/non-ferrous metal cladding on glass/ ceramics is also known where the silver/other non-ferrous metal sheets are cut into required design, shape and size and pasted with the help of some
UV or non UV adhesive. The major disadvantage to the above process is that:
• Cutting the design out of thin Silver/other non-ferrous metal
sheets is a very laborious job and many times intricate designs
cannot be cut.
• Pasting the cut design on to the glass/ ceramic surface is an
equally difficult task. The sheet can be conventionally pasted
on flat surfaces only. It is very difficult to process curved
surfaces as it will lead to warping defects.
Another conventional method is where silver stencils are made from proprietary Silver Chemical Compounds. These stencils are then transferred to the glass/ceramic surface and heated to a very high temperature. The chemical silver is converted into the metallic silver and gets fused into the glass/ceramic surface. This coating is quite adherent and can be further electroplated to achieve the required thickness. However, this is again a very expensive process and only flat surfaces can be processed. Therefore this process is not suitable for coating glass/ceramic surfaces with all kinds of curves and curvatures. Besides heating glass/ceramics to high temperatures, involves high costs and breakages.
Another conventional method is based on the fact that glass/ ceramics surface can be metallized with Plasma Arc Gun using Silver wires. However, this process is not suitable for cladding silver/other no-ferrous metal on glass/ceramics for the following reasons:
• Glass/ceramics can't be metallized easily with Plasma Arc as
the process generates large amount of heat and the
metallised surface produced is very rough.
• The adhesion is very poor.
• This process is very inefficient as only 30-40% of the metal is
transferred to the glass/ceramics surface while the rest of the
metal gets burnt, thus making the cost of production
abnormally high.
Another conventional method is based on the technique that glass/ceramic surface can also be metallized by applying a thin layer of lacquer on the glass/ceramic surface and spraying a thin coating of a metal powder on the still wet lacquer layer followed by drying in an appropriate atmosphere. Silver/other non-ferrous metal can be deposited on said metallized layer. This process also has a very poor adhesion, and other drawbacks like rough surface.
Again as per another existing technique silver/other non-ferrous metals can be deposited by various Vapor Deposition techniques, such as Sputtering which requires highly critical equipment and workforce which is so expensive that the whole project becomes unviable.
Hence there arises a need to develop a simple and economic technique to clad silver/other non-ferrous metal on glass/other non-conductive surfaces like ceramics, porcelain etc., more so
when intricate patterns are required to enhance the value of the product.
OBJECT OF THE INVENTION
A major object of the present invention is to clad silver or any other nonferrous metal on glassware and ceramics using the electroforming technique.
Another object of the present invention is to provide an economical process for cladding silver/nonferrous metals on glassware and ceramics at room temperature.
Yet another object of the present invention is to process glassware and ceramic articles of any shape and size with superior quality.
Still another object of the present invention is to flexibly clad silver/nonferrous metals onto glassware and ceramics in various patterns.
A further object of the present invention is to achieve cladding of high quality in terms of neatness, surface finish and strength of adhesion.
SUAAAAARY OF THE INVENTION
This invention relates to a process for cladding silver or non ferrous metals comprising the steps of:
i. Masking of glass/ceramic surface, ii. Cleaning and roughening of the unmasked surface, iii. sensitizing said roughened surface with a chemical
solution, iv. spraying a solution on said sensitized surface to form a
silver/nonferrous metal film, v. electroforming silver/nonferrous metal on the surface
in step (iv), to obtain silver/nonferrous metal cladded glass/ceramic surface.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 relates to masking of the glassware or ceramics
Fig. 2 relates to roughening of the glassware or ceramics.
Fig. 3 relates to sensitization of the glassware or ceramics.
Fig. 4 relates to spraying silver/nonferrous metals on the glassware
or ceramics.
Fig. 5 relates to electroforming silver/nonferrous metals on the
glassware or ceramics.
Fig. 6 relates to polishing of the electroformed glassware or
ceramics.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The glass/ceramic surface 1 is masked with a negative mask of the selected design. The negative mask ensures that the surface which is to be coated with silver/nonferrous metals is unmasked and the
surface which should not have any coating of silver/nonferrous
metals is protected with an appropriate mask 2 (Fig. 1) material.
The unmasked surface is roughened to achieve a larger surface area
for obtaining the required bond strength. The roughened surface 3
(Fig. 2) is obtained by sandblasting the unmasked surface or by
treating with a mixture of certain acid which etch the glass.
The roughened surface is sensitized or activated with a proprietary
chemical solution for adsorbing a layer 3a (Fig. 3) of metal ion on
the surface 3.
A silver film 3b (Fig. 4) is deposited on the sensitized surface by
spraying the reducing and silver containing solution simultaneously
on said surface.
Silver/nonferrous metal is now electroformed on the glass/ceramic
surface to obtain a cladding of silver 3c (Fig. 5) on said surface.This
results in obtaining a sufficient thickness of the layer that would be
able to sturdily stand on its own if the substrate glass/ceramic is
removed.
Lastly, surface finishing is required to obtain a smoothened surface
3d (Fig. 6). Various grinding and polishing operations are carried out
to achieve highly leveled, scratch free, mirror bright surface.
DESCRIPTION OF THE INVENTION
Silver/nonferrous metals can be clad on non-conducting surfaces mainly glassware and ceramics by metallization of said surface with a thin layer of metallic silver/nonferrous metal coating which is quite adherent to the surface and which can be further
electroplated with ease. The non-conducting surfaces include glassware, ceramics, porcelain, pottery, stoneware. The process involves the following steps:
STEP 1. MASKING
A hand sketch is converted into a computer generated design with the help of appropriate Software. This design is transferred onto a suitable masking material, which acts as a Mask for further processing. Vinyl can be used as a masking material. Following parameters are considered while selecting the masking material:
a) Intricacy of the design
b) Type of the glass and ceramic being used

c) Amount of surface roughness required in subsequent processes,
so as to ensure sufficient adhesion of metal.
d) Type or material of glass/ceramics being used
e) Thickness of the Masking Tape
Considering all of the above parameters a suitable Masking Tape is selected and the selected design is transferred onto it. The component onto which the Masking Tape is to be applied is cleaned by using suitable alkali based degreasing chemicals such as sodium triphosphate, sodium metal-silicate, sodium carbonate and wetting agents. This treatment ensures proper cleaning of the component surface. All contaminants such as oil, grease, or any other loosely adherent dust particles are removed. Once the component is thoroughly cleaned, it is rinsed with running water
and dried. This cleaning process facilitates good adhesion of the Mask to the component surface.
The component is masked with a NEGATIVE mask of the selected design. The NEGATIVE mask ensures that the surface which is to be coated with silver/ nonferrous metals is unmasked and the surface which should not have any coating of silver is protected with an appropriate mask.
STEP 2. SURFACE ROUGHENING
The unmasked surface is roughened to achieve a manifold larger surface area which is instrumental in achieving the required bond strength .This roughening is achieved by using proprietary Roughening Compounds in Special Purpose Machines specially designed for this application by spraying the abrasive material at the appropriate pressure.
In this process of roughening, the component's surface is blasted with the assistance of high pressure air, with a suitable type of abrasive. Or as an alternative it can be treated with a mixture of certain acid which etch the glass surface. Thus the surface becomes rough and this rough surface is helpful in achieving the proper mechanical bonding of the Silver/ nonferrous metals cladding to the surface of glass/ceramic, on the basis of "Tongue in Groove" principle.
Since glass and ceramic are not conductors of electricity, electroforming through high speed electroplating is difficult. Hence
glass/ceramic is made conductive by sensitizing, spray silvering/ nonferrous metals and stabilization as explained below.
STEP 3. SENSITIZING
At this stage the unmasked roughened surface is treated with a proprietary chemical solution which sensitizes the glass and ceramic surface. One of such solutions comprises of stannous chloride(10g/l) and hydrochloric acid(40 m/l) solution.The solution is used at room temperature and the time of immersion is one to five minutes, the articles preferably being agitated mechanically during this period. A more preferred solution which gives better results on spraying comprises of stannous chloride(30g/l), stannic clhloride(3g/l), hydrochloric acid(40m/l) and sodium chloride(175g/l). The said solution is made by dissolving stannous chloride and stannic chloride in concentrated hydrochloric acid, the solution is diluted and the sodium chloride then dissolved before making upto working volume. These solutions may be contained in a tank or sprayed on the work through a single-jet spray gun. After being sprayed or dipped in a sensitizer the glass must not show any water breaks. As a result of sensitizing, a layer of a metal ion is adsorbed on the surface. The sensitizing procedure enhances the uniformity and adhesion of the deposit and the speed of deposition and the thickness obtainable.
STEP 4. SPRAY SILVERING
A silver/ nonferrous metal film can be now be formed on the sensitized surface. At this stage 2(Two) proprietary solutions, one

containing the silver and the other the reducer are sprayed simultaneously through a special 2(Two) Nozzle Spray Gun in such a way that the chemical Silver is reduced to metallic Silver at the surface of the component. The Silver film is formed in a matter of seconds. One of the silver containing solutions is ammoniacal silver nitrate and one of the reducing solution is hydrazine hydrate. This process offers advantage of simplicity of operation, superior bond strength, high production rates, and much higher efficiency of silver utilization than other methods.
STEP 5. STABILIZATION
The freshly formed film of silver/ nonferrous metals is very delicate and can't be handled immediately. Therefore the component is dried in warm dry air for the moisture to evaporate and the coating makes a mechanical bond with the glass and ceramic substrate.
STEP 6. ELECTROFORMING
Silver/ nonferrous metal is electroformed onto glass/ceramic in order to achieve a sufficient thickness of the layer of silver/ nonferrous metal that would be able to sturdily stand on its own if the substrate glass/ceramic is removed. After stabilization the component is ready for Electroforming. Proper contact points are made on the metallized surface for current to pass. The component is properly jigged in a holder and placed in an Electroforming Tank. This Electroforming Tank contains a proprietary Electroforming solution. During the Electroforming process the following parameters are duly considered:
a) Chemical composition as adjusted for our requirements.
b) Operating conditions, in terms of Temperature, Applied Current
Density, Solution Circulation, Anode Distribution etc;
c) Vigorous solution circulation
d) Continuous filtration at high speed

e) Continuous mechanical movement of the glass/ceramic
component as per the techniques developed by us
f) Regular additions of the additives for the grain refining and
improved surface finish.
g) Uniform thickness distribution all over the surface
f) Weight control of the coating
It is important that the electrical connection to the cathode rod be made immediately the articles are immersed in the plating solution, otherwise the silver/nonferrous metal deposit may dissolve before the electrodeposit is applied. The components are electroformed initially at a low current density ( 0.2 amp/dm2) for ten minutes without agitation and after this the current should slowly increase upto the working level and at the same time the agitation can be proportionately increased.
STEP 7. SURFACE FINISHING
Finally the Plated surface is smoothened. This operation is carried out considering the following factors:
a) Initial surface finish
b) Shape of the component
c) Intricacy of the Design fabricated on it
Various Grinding and Polishing operations are carried out to achieve highly leveled, scratch free, mirror bright surface. This process ensures the passing of the required current on the glass/ceramic surface, adequate mechanical bonding of the metal onto the glass/ceramic, a good finish, intricate and contoured forms of glassware, ease of operation and economy of cost.

We Claim:
1. A process for cladding silver or non ferrous metals comprising
the steps of:
i. cleaning and masking of glass/ceramic surface, ii. roughening of the unmasked surface, iii. sensitizing said roughened surface with a chemical
solution, iv. spraying a solution on said sensitized surface to form a
silver/nonferrous metals film on the sensitized surface, v. electroforming silver onto the surface in step (iv), to obtain a silver/nonferrous metal cladded glass/ceramic surface.
2. The process as claimed in claim 1, wherein the unmasked
surface is cleaned by using alkali based degreasing chemicals
followed by rinsing with deionised water.
3. The process as claimed in claim 2, wherein the alkali based
degreasing chemicals are sodium triphosphate, sodium meta-
silicate, sodium carbonate and wetting agent.
4. The process as claimed in claim 1, wherein the sensitizing
solution comprises of stannous chloride and hydrochloric acid.
5. me process as claimed in claim 1, wherein the sensitizing
solution preferably comprises of stannous chloride, stannic
6. The process as claimed in claim 1, wherein the solution
sprayed comprises of ammoniacal silver nitrate solution and a
reducing solution.
7. The process as claimed in claim 6, wherein the reducing
solution is hydrazine hydrate.
8. A process of cladding silver or nonferrous metals on glass/ceramic surface substantially as herein described with reference to the accompanying drawings.