A Method and Apparatus for Faster and Reproducible Patination Process for Alloys used in Bidriware

Category- Advance Material & Manufacturing

Industry Classification:

NIC (2008)- 2592- Machining, treatment and coating of metals; 20224- Manufacture of prepared pigments and other coloring matter of a kind used in the manufacture of paints or by artists or other painters;
Applications- Material processing which includes Lasers, optical methods, LIBS analysis, additive manufacturing, welding and cutting
Market drivers: The handicrafts market in India achieved a size of US$ 4,277.5 million in 2023 and is projected to reach US$ 7,817.8 million by 2032, with a compound annual growth rate (CAGR) of 6.9% during the period

Bidriware, the sleek and smooth dark colored metalwork with intricate eye-catching designs on its glossy surface, is famous all over the world.
The conventional patination process (black/dark background), uses a mixture of ammonium chloride (NH4Cl) and the clay taken from the surrounding of the Bidar fort wall. As the fort is now a heritage center the use of sand is prohibited, making the livelihood of artisans difficult and threat for the art.
There is a need in the art for a viable chemical substitute, an alternative procedure of the process and an apparatus, which can provide faster, efficient way of patination.

The patination process developed involves immersion of the Zn-Cu alloy in a solution containing NH4Cl and alkali nitrates (K/Na/Ca-nitrates) in a certain ratio dissolved in water. The chemical solution is then heated to and maintained at 70 ºC.
The specimen is immersed in the patination solution for a certain period of time. Upon exposure of the specimen to the patination solution, electrochemical dissolution of Zn/ or Zn rich phase occurs on the surface leading to the enrichment of Cu/Cu rich phase on the surface. This Cu enriched surface undergoes oxidation in the patination solution to form a black colored oxide (patina)
Zinc in the alloy preferentially dissolves into the solution leading to a Cu enriched surface, which then oxidizes to form the patina.
An apparatus has been conceptualized, designed and fabricated for automation of the patination process
The patinated surface was characterized using X-ray diffraction (XRD), Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS)

The process successfully imparts a black patina similar to the one observed in Bidri craft.
The process developed completes the patination process within 20-30 seconds which is much faster compared to another recently patented process.
The process uses easily available chemicals and a simple yet automated apparatus to carry out patination. This process would help in augmenting livelihoods of artisans and increase production of Bidriware by reducing dependence on unsustainably extracted soil from heritage structures.

Prof. Dr.-Ing. Lakshman Neelakantan

Corrosion Engg. and Materials Electrochemistry Lab

Prof. Manas Mukherjee

Department of Metallurgical and Materials Engineering

TRL 4

Technology Validated in Lab

Technology Transfer