How to Clean a Brass Diya: Tamarind, Salt and Sense
A brass diya cleans with an acid and a mild abrasive, and almost nothing else. Tamarind pulp or a cut lemon, a pinch of salt, and some patience will do what a bottle does. The part that gets skipped is the order: wash the burnt oil off first, because no acid can reach metal through a film of old ghee.
Key takeaways
- The dark layer is copper sulphide — tarnish formed by sulphur in the air. It is not dirt, and brass cannot rust.
- Every method that works is the same two things: an acid to dissolve the layer, a mild abrasive to lift it away.
- Order beats recipe. Grease comes off first, tarnish second, water off completely last.
- Brass and kansa are different alloys, and lacquered brass should not meet acid at all.
What is the black stuff on a brass lamp?
It is the metal reacting with the air, which is a slower and less alarming thing than it looks.
Brass is an alloy of copper and zinc — generally about two-thirds copper to one-third zinc. The copper is the part that reacts. It combines with sulphur in the air to form a brown and eventually black surface layer of copper sulphide. Left somewhere damp for long enough, that layer can oxidise further into a green-blue copper carbonate.
Two things follow, and both are useful. Brass contains no iron, so it cannot rust — it corrodes, which is a different problem. And the layer is thin. You are removing something microns deep, not resurfacing the lamp.
| What you see | What it is | What it needs |
|---|---|---|
| Warm gold going dull and brownish | early copper sulphide | an acid wipe, a couple of minutes |
| An even, settled black | thicker copper sulphide | acid plus abrasive, and real pressure |
| Green or blue-green crust | copper carbonate, from damp storage | removal in full before the lamp holds oil again |
The third row is the only one worth hurrying over. A green crust means the lamp has been sitting somewhere it should not have been, and it tends to come back in the same spot.
Why tamarind, and not a bottle of polish?
Because they are doing the identical thing, and one of them was already in the kitchen.
Tamarind pulp carries tartaric acid. Lemon carries citric acid. Either will dissolve the copper compounds on the surface and turn them into salts that rinse away. The pinch of salt, or the ash from the stove, is not folklore either — it is the abrasive that lifts the loosened layer off so the acid can reach what is underneath. Acid and abrasive. That is the entire method, and a tin of commercial brass polish is the same two ideas sold together.
My grandmother kept a lump of tamarind aside on cleaning days, separate from the cooking imli, going slowly darker in its bowl. I was told it was because it was cheap. It was cheap. It was also correct, which nobody mentioned, possibly because nobody had been told either.
One honest note on the sourcing. The practice of polishing brass shrine lamps and copper vessels with tamarind pulp is documented in print most clearly for Buddhist Asia, Myanmar especially. In Indian households it is everywhere and written down almost nowhere — it travels hand to hand, grandmother to whoever is standing in the kitchen. The absence of a citation is not evidence that the method is young.
What is the right order to clean a lamp?
This is the part that decides whether the work holds.
- Degrease. Hot water and dishwashing liquid, with a soft brush at the wick notch where carbonised oil collects. Acid will not touch metal through grease, so a lamp that skips this step comes out patchy and gets blamed on the tamarind.
- Rub with acid and abrasive. Tamarind pulp with salt, or half a lemon dipped in salt, worked over the surface. Give it a minute to act rather than attacking it immediately.
- Rinse properly. More thoroughly than feels necessary. Acid left in an engraved line keeps working after you have stopped looking.
- Dry completely and at once. Not on the draining board. A cloth, then air, then put it away. Most lamps that blacken again within weeks were put away damp.
If the lamp is going back into storage rather than straight back into use, the thinnest possible wipe of oil slows the next round of tarnish considerably.
Is it brass, or is it kansa?
Worth settling before you start, because the two do not behave the same and only one of them comes up gold.
| Metal | What is in it | How it reads |
|---|---|---|
| Brass | copper and zinc, roughly two to one | warm gold; the usual diya, thali and lota |
| Bell metal (kansa) | copper and tin, about 78 to 22 | pale, silvery, slightly brittle; plates and offering vessels |
| Copper (tamba) | copper | pink-brown, tarnishes fastest of the three |
| German silver | nickel, copper, zinc — no silver | bright white; often mistaken for the others |
Bell metal is called kansa in West Bengal and Odisha, kanh in Assam, kanchu in Kannada, and it is what the bata and banbati offering vessels are made from. The acid-and-abrasive method works on it perfectly well. What it will not do is turn it gold, because there is no zinc in it to be gold — so stop when it is clean rather than rubbing on in hope.
The one metal to keep acid away from is lacquered brass, which is brass under a clear sealed coat. It looks like brass and never tarnishes, which is the tell. Acid strips the lacquer in patches and the piece then tarnishes unevenly underneath, which is a far worse state than where it started. If water beads on it and it has stayed bright for years with no attention, leave it to a damp cloth.
When should you not clean a brass lamp at all?
More often than the internet suggests.
An old lamp that has gone dark over decades is carrying a patina, and on an inherited or temple piece that darkness is frequently the point — it is not reversible once you have taken it off. The sensible compromise is to clean the wick area so the lamp burns cleanly and leave the body alone. The same applies to anything with maker's marks or visible age, where a hard polish removes exactly the evidence that made it interesting.
A lamp in daily use is also allowed to look used. There is no rule that a working diya must be mirror-bright, and a brass holder darkening where the smoke touches it is doing what brass does.
What about the week before Diwali?
The metal in a house tends to get dealt with in the run-up, and this year the cluster falls on Dhanteras, Friday 6 November 2026, with Diwali itself on Sunday 8 November.
Do the lamps a few days ahead rather than the night before. Not for any ritual reason — simply because a lamp needs to be completely dry before oil goes into it, and a rushed job on the evening itself means wicks sitting in a film of water. Whether that oil is ghee or til matters less than whether the lamp was dry when it went in.
What is left of the method
Not much, and that is the appeal. An acid, something gritty, hot water first and a dry cloth last. No equipment, nothing to buy, and a result you can see in the first thirty seconds of rubbing.
What I did not understand as a child, watching a lump of tamarind do this, was that it was chemistry and not thrift. Knowing that does not make the lamp any brighter. It does mean that when the black comes back in March, you know what it is and what to do about it, which is most of what anyone wants from a household skill.
Questions people ask
What is the black coating on a brass diya?
It is tarnish, not dirt and not rust. Copper in the brass reacts with sulphur in the air to form a brown and eventually black layer of copper sulphide. Brass has no iron in it, so it cannot rust.
Can I use tamarind instead of brass polish?
Yes. Tamarind pulp supplies tartaric acid, a pinch of salt supplies the abrasive, and that is the same pairing a commercial polish uses. The commercial product is faster and more uniform; the tamarind is not a compromise.
Why does my lamp go black again within weeks?
Usually because it was put away damp, or because it sits in a kitchen. Tarnish restarts wherever moisture and sulphur reach the metal, so drying the lamp completely matters more than how hard you rubbed it.
Should I clean an old temple lamp that has gone dark?
Often not. A deliberately kept patina on an old or inherited lamp is part of its value, and stripping it is not reversible. Clean the wick area so it burns properly and leave the rest.
Is kansa cleaned the same way as brass?
The same acid-and-abrasive method works, but kansa is bell metal — copper and tin, not copper and zinc — so it is pale and silvery and will never come up gold. Do not keep rubbing expecting a brass colour.
