Question

Aluminum sculpture can be given a black patina by immersing the sculpture in a bath of solution made from the following chemicals:
(A) Copper Sulphate
(B) Caustic Soda
(C) Acetic Acid
(D) Calcium Chloride
(E) Water

• A. (A), (B), (C), (D), (E)
• B. (A), (B), (E) and (D)
• C. (B), (C), (E) and (A)
• D. (B), (D) and (E) only

Hint:

Patination of aluminum often involves strong alkalis like caustic soda to break down the passive oxide layer and allow the surface to react.

Answer 1

The Correct Option is D

Step 1: Understand the chemical process of patination. Patination involves creating a chemical reaction on the metal's surface to alter its color and texture. For aluminum, a strong alkali or a specific salt solution is often used.
Step 2: Analyze the chemicals. Caustic Soda (Sodium Hydroxide) is a strong alkali that etches the surface of aluminum, which is a key step in many blackening processes. Water is the universal solvent for the bath. Other chemicals act as modifiers.
Step 3: Evaluate the combinations. A common chemical bath for producing a black smut on aluminum involves a hot solution containing caustic soda and other salts. The combination of (B) Caustic Soda, (D) Calcium Chloride, and (E) Water creates a viable chemical solution for etching and coloring the aluminum surface. Other combinations are less chemically conventional for producing a black patina on aluminum.