Onyx is the most seductive stone in the library and the most demanding to keep. It is a calcareous stone — chemically close to marble — banded with translucent layers that glow when lit from behind. That same translucency comes from a soft, porous structure, and softness is the whole story of caring for it.
What onyx is
Despite the name, commercial “onyx” is not the quartz onyx of jewellery. It is a banded calcite, deposited slowly by mineral springs. The bands you see — honey, amber, green, white — are growth layers, and light passes between them.
Treat onyx like a silk garment, not a worktop: beautiful, expressive, and happiest away from heat, acid and standing water.
Why it needs care
Onyx sits at roughly 3 on the Mohs scale — softer than a steel knife. It is porous, so it absorbs liquids, and it is calcareous, so acids etch it: lemon, wine, vinegar and many household cleaners will leave a dull mark even after a brief contact.
- Acidic spills etch the surface — blot, never wipe across.
- Standing water leaves rings on unsealed stone.
- Abrasive pads and powders scratch the polish.
A daily routine
Dust with a soft, dry microfibre cloth. For cleaning, use warm water and a pH-neutral stone soap — nothing acidic, nothing alkaline. Dry the surface afterwards rather than letting it air-dry, which prevents water rings on horizontal pieces.
Sealing & deep cleans
A penetrating (impregnating) sealer buys you time against stains by slowing absorption. Reseal roughly once a year on vertical work and more often on anything that gets wet.
Caring for back-lit panels
Lit panels add one concern: heat. Use low-heat LED light boxes, leave a ventilation gap, and keep cleaning to the front face only — the mesh-and-resin backing should never get wet.