Before you try anything: always speak to a professional before cleaning, treating or applying any product to your stone. Every slab is different, and the wrong product can cause permanent damage. Contact us or a qualified stone restorer first.
Quick answer
Oil stains in onyx need a solvent poultice: mix acetone or mineral turpentine with an absorbent powder, spread it over the stain, cover with plastic and leave it 24 to 48 hours. For fresh spills, sprinkle cornflour or talc on first to soak up as much oil as possible.
First, check what you are dealing with
- Darker, slightly translucent patch: oil. Follow the steps below.
- Dark patch that fades as it dries: water, not oil. Leave it to dry.
What you need
- Cornflour or talc
- Acetone or mineral turpentine
- Flour, talc or diatomaceous earth
- Plastic wrap and tape
- Plastic scraper
- Gloves
- Good ventilation
Step by step
Soak up fresh oil
If the spill is fresh, cover it with a thick layer of cornflour or talc and leave it for a few hours to absorb what it can, then brush it away.
Test first
Try the mixture on a hidden spot of your onyx (inside a cut-out or under an overhang) and check the finish after it dries.
Mix the poultice
Stir an absorbent powder (plain flour, talc, diatomaceous earth or whiting) into acetone or mineral turpentine (open a window and keep flames away) until it has the consistency of peanut butter.
Apply it
Spread it 5 to 6 mm thick over the oil stain, extending about a centimetre past the edge. On onyx, stick to 3% peroxide and check after 24 hours rather than 48.
Cover and wait
Cover with plastic wrap, tape the edges and poke a few small holes so it dries slowly. Leave it 24 to 48 hours until completely dry: the drying is what pulls the stain up into the powder.
Remove and rinse
Lift the dry poultice with a plastic scraper, rinse with clean water and dry the onyx. If the oil stain is lighter but still there, repeat up to three times.
What not to use on onyx
- Vinegar, lemon juice or "natural" citrus cleaners: they etch onyx.
- Scourers, steel wool and abrasive creams on a polished surface.
- Mixing cleaning chemicals, especially bleach with anything else.
- Heat guns or hairdryers, which drive oil deeper.
- Scrubbing with degreasers, which spread the stain.
When to call a professional
Deep, old oil stains, or oil in resin-filled areas, are best left to a stone restorer. Onyx needs a restorer who works with it regularly: it is softer and more fragile than marble and easy to over-polish.
Understanding oil and grease stains on onyx
Architectural onyx is banded calcite. It is less absorbent than limestone, but its translucency means a stain can show from both sides of a backlit piece.
Onyx needs a restorer who works with it regularly: it is softer and more fragile than marble and easy to over-polish.
Good to know
Oil on onyx dims its translucency in that spot, so it is most obvious on backlit pieces. Use short, gentle poultices and ask an onyx specialist if it persists.
Stop it happening again
Whether yours is honey, white, green and pink banded onyx, often backlit, repairing it fixes today's mark; protecting it stops the next one. Our clear Stone Protection Film sits over the surface, so acids cannot etch it and liquids cannot soak in. Onyx is usually polished, so Gloss film is the natural match and keeps its reflective depth. It is installed across Sydney with a 10-year written warranty.
How we protect onyx · Stain removal guide · Oil & grease stains on every surface