1) Title of the invention
Alternate Blackening Process for Bidriware
2) Field of invention
Bidriware Artifacts / Handicraft
3) Use of invention
The alternate process developed is for the blackening of Bidriware artifacts.
4) Prior art
Bidriware is one of the rarest and most intricate art forms of India. Bidriware is a metal handicraft from Bidar of Karnataka State. F&F Division team visited Bidar to study the manufacturing process and prepared a Report. The process steps being followed are as below.
Stepl) The manufacturing of the casting by preparing sand mould, melting & pouring the Zinc-Copper alloy. Castings are finished by polishing and buffing.
Step 2) The desired designs are marked on the casting using marking tools manually.
Step 3)The designs are engraved manually on the casting with sharp chisels /tools.
Step 4) Fine wire or flattened strips of pure silver are then carefully hammered / inlaid into these grooves.
Step 5) The artifact then is filed, buffed and smoothened. This results in rendering the silver inlay hardly distinguishable from the gleaming metallic surface which is now all silvery white.
Step 6) The artifact is immersed in mix to blacken the Zinc-Copper portions
The process used by Bidriware artisans to blacken the artifacts is by immersing the artifact in a mix comprising of a special variety of soil (which is available only in the Bidar fort), Aluminium Fluoride and water. The components are mixed to form a thick solution which is then brought to boiling and then the article is immersed inside.
5) Draw backs of prior art
a) The soil used for the final blackening process is extracted from certain portions of Bidar Fort. Extraction of the soil from the Fort can weaken the structure and hence the availability of soil is limited. Due to the scarcity of the sand, Bidriware

art is in danger if alternate methods are not developed for the blackening process, b) Aluminium Fluoride used for making the mix is health hazardous.
6) Comparison between prior art and present invention
Prior art uses Soil from Bidar Fort and Aluminium Flouride for the blackening process. The soil is scarce in nature & Aluminium Flouride is hazardous to health.
The present process developed has the following advantages
a) The alternate process is developed with the use of chemicals which are commercially available.
b) The chemicals are environmental friendly and non hazardous.
7) Aim of the invention
Aim of the invention is to develop an alternate process for Blackening of the Bidriware artifacts using commercially available chemicals which are not hazardous to health and environment friendly.
8) Summary of the present invention
a) The artifact was analysed to identify the exact chemical composition present in the Bidriware. The soil was analyzed to find out the composition so as to understand the chemical reaction which is resulting the blackening of Zinc-copper alloy.
b) An alternate process with commercially available, environmentally friendly process for blackening of the Bidriware artifacts was developed.
9) Brief description of the drawings:
. Figure 1: Original Bidriware artifact Figure 2: Test piece by HAL
10) Statement of invention
An alternate process for Blackening of the Bidriware artifacts was developed.
11) Detailed description of invention
The main process steps followed in manufacturing of Bidriware Artifact are
Stepl) The manufacturing of the casting by preparing sand mould, melting and pouring the Zinc-Copper alloy. Castings are finished by polishing and buffing.

Step 2) The desired designs are marked on the casting using marking tools manually.
Step 3) The designs are engraved manually on the casting with sharp chisels / tools.
Step 4) Fine wire or flattened strips of pure silver are then carefully hammered / inlaid into these grooves.
Step 5) The artifact then is filed, buffed and smoothened. This results in rendering the silver inlay hardly distinguishable from the gleaming metallic surface which is now all silvery white.
Step 6) The artifact is immersed in mix to blacken the Zinc-Copper portions
During Blackening process, Zinc-copper alloy portion of the artifacts is selectively darkened while there is no effect on the silver inlay. This gives an excellent appearance to the artifacts with shiny silver design in black background.
Current practice being followed by Bidriware artisans to blacken the artifacts is by using a mixture prepared using the special variety of soil which is available only in the Bidar fort, Aluminum Fluoride and water. The components are mixed to form a thick solution, the solution is brought to boiling and then the article is immersed inside. During this process the Zinc-copper alloy portion turns black whereas there is no effect on the silver inlay.
Bidh soil is a key element in the Blackening Process which provides an excellent matt finish to the Bidriware. The soil used for the final blackening process is extracted from certain covered, unlit portions of Bidar Fort. Artisans say that the soil of Bidar is very special and no one knows exactly what is special about it. Artisans feel that the soil has been away from sunlight and rain for years and therefore it has great oxidizing properties. It is tasted by the artisans by their tongues who then decide whether it is fit for use or not. This knack comes from experience and is passed on to next generations.
The soil extraction of the soil is restricted since mining of the soil from the Fort can weaken the structure. If alternate blackening processes are not developed, Bidriware art may not survive longer. Also Aluminum Fluoride used for making the mix is health hazardous.
F&F Division has taken up the development of an alternate Blackening process. In order to study the process, a team from F&F Division visited Bidar and following samples of Bidriware, Soil & Aluminium Flouride were collected.
The Bidri artifact was subjected for base metal analysis and outer surface (blackened area and silver inlay) analysis was carried out by Analytical techniques like XRF (X-ray Fluorescence) and EDAX(Energy Dispersive X-ray Spectroscopy).The topographical

features of the blackened surface is analyzed by SEM (Scanning Electron Microscope) and coating thickness analysis was done by using Dualoscope coating thickness tester. The Bidar Fort soil was analyzed for certain parameters like pH, conductivity and composition. It was found that Aluminum Flouride used in the current process is health hazardous, the use of the same could harm the Bidriware artisans.
Development of an alternate blackening process was taken up with following considerations.
a) The alternate process should be with the use of chemicals and raw materials which are commercially available.
b) The chemicals should be environmentally friendly.
c) The cost of the raw materials should be affordable.
d) The Blackened layer should be permanent.
Details of Experiments conducted at F&F Division
Manufacture of Zinc-Copper Casting test pieces
To conduct the actual trials/ experiments, casting test pieces were manufactured
a) Using the exact composition used for making Bidriware.
b) As sand casting which is the process currently being followed
c) The casting was polished as per the current process
d) A silver piece was inserted into the casting
e) Blackening of the artifacts
Preparation of the solution and development of Blackening Process
Based on the results obtained on above parameters, various combinations of salts was formulated (keeping in view of commercially availability, non hazardous and eco friendliness). Many trials were conducted to optimize the process parameters. Various combinations of chemicals were prepared and experiments were conducted to arrive at the optimum coating thickness. Finally the process was optimized using a mix of salts and acid mixed with 100. ml of tap water. The process steps for the blackening of Zinc-Copper alloy test pieces are optimized as given below.
Step 1) A mix of salts and acid mixed with 100 ml of tap water to be added. Step 2) Stirring is done to get a clear solution.
Step 3) The mirror polished (buffed) artifact are wiped with clean cotton cloth. Step 4) The above parts are immersed in the solution.

Step 5) Stir constantly using wooden rod or by passing compressed air.
Step 6) After every 20 minutes, the position of the part to be altered so that every part
is exposed to the solution. Step 7) After 60 minutes, the part to be taken outside and the part to be immersed in
hot water at a definite temperature and for few minutes. Step 8) Part is washed in running tap water. Step 9) Part is wiped with cotton cloth to remove traces of water. Step 10) Continue with existing practice of polishing with coconut oil & silvo.
Testing of Zinc-Copper casting using the new process
The cast test pieces were subjected to the alternate blackening process using the solution prepared. The topographical features of the blackened surface was analyzed by SEM and coating thickness by Dualoscope coating thickness tester , all the values were in comparison with that of Bidriware artifact. The elemental composition of the same was checked by XRF analysis and EDAX, which revealed similar chemical composition as that of Bidriware artifact.
Also experiment was conducted by inserting a Silver piece into the Zinc-Copper cast piece and blackening process was conducted. Zinc-Copper portion was turned black whereas the silver inlay was unaffected.

1
"We claim"
1. "Alternate Blackening Process for Bidriware" developed at Foundry & Forge Division, Hindustan Aeronautics Limited is a new process developed for the Blackening of Bidriware Artifacts, the details of which are not available in open literature.
2. The process has been developed by Foundry and Forge Division of HAL, Bangalore and the process parameters are optimized for the blackening of the Bidriware to give proper Blackened layer.
3. The use of alternate chemical solution in place of Soil from Bidar Fort and Aluminium Fluoride is a new concept for blackening of the Bidriware artifacts to give a matt finish to the Bidriware. Also the alternate chemical solution selectively darkens the Zinc-Copper alloy portion while it has no effect on the silver inlay.
4. The composition of solution is optimized.
5. The process is effective for all types of Bidriware.