A "Sparkling" Insight: Learning Through Silverware Cleaning

When I volunteered at the American Cancer Association Discovery Store, one of my jobs was to polish donated silverware. I noticed that some of the silverware had turned black. At first, I thought the black stains were just old grease or dirt, but it was not easy to clean them off by regular detergents. I had to use special polish cream. That made me wonder — why does silverware get black stains and dirty-looking over time? And how does the polishing cream make it shiny again?

The Science Behind It

Silverware turns black because of a chemical reaction. Silver, the metal used in silverware, reacts with a gas in the air called hydrogen sulfide (H₂S). Even though there's only a tiny amount of this gas in the air, it’s enough to cause a reaction over time.

When silver reacts with hydrogen sulfide, it forms a new substance called silver sulfide. Silver sulfide is black, and it sticks to the surface of the silver, which we call tarnish.

Overall Tarnish Reaction:

2Ag(s) + H2​S(g) → Ag2​S(s) + H2​(g)

• Ag = silver metal

• H₂S = hydrogen sulfide gas (from pollution, foods like eggs, etc.)

• Ag₂S = silver sulfide (black solid tarnish)

• H₂ = hydrogen gas (usually in trace amounts, not visible)

This reaction actually involves oxidation and reduction (a redox process):

• Step 1: Silver gets oxidized (loses electrons):

  2Ag → 2Ag+ + 2e−

• Step 2: Sulfide from H₂S gets reduced (gains electrons) and reacts with Ag⁺:

S^2− + 2Ag+ → Ag2​S

The sulfur in H₂S acts as a reducing agent, and the silver gets oxidized.

Where Does Hydrogen Sulfide Come From?

Hydrogen sulfide can come from:

• Polluted air

• Foods like eggs, onions, and garlic

• Rubber or wool items stored nearby

• Even your sweat (which has sulfur-containing compounds)

That’s why silver that’s stored away or touched often might tarnish faster.

How Does Polishing Cream Work?

When I used the silver polishing cream at the Discovery Store, it was very effective — the tarnish disappeared quickly, and the silver sparkled again!

The polishing cream usually contains mild abrasives and chemicals that either:

1. Physically scrub off the black silver sulfide layer (kind of like gentle sandpaper), or

2. Chemically react with the silver sulfide and turn it back into silver, or into something that can be wiped away.

Some creams also leave a thin layer of protection to slow down tarnishing in the future.

What I Learned

Working with silverware made me realize how science is part of everyday life — even in simple chores like cleaning.