Onyx in Interiors: Backlighting and Applications

Onyx is a translucent decorative stone; in the trade the name mostly refers to onyx marble, a banded variety of calcite or aragonite formed from mineral spring deposits. Its main feature is the ability to transmit light: when backlit, an onyx slab glows from within, revealing a banded pattern in honey, green, white, pink and amber tones.

The key selection criterion is purpose: onyx is an interior stone. It is soft, brittle and sensitive to acids, so it belongs on walls, bar counters, feature panels and in bathrooms, but not outdoors or in high-wear areas.

Onyx is chosen by interior designers and architects of hotels, restaurants, and premium residential and public spaces. Other rocks are covered in the section Natural stone for facades and interiors.

Onyx marble forms in caves and near hot springs through the slow deposition of calcium carbonate from water. This gives the stone its characteristic layered, banded texture: each band is a separate layer of deposits with its own impurities, which produce the colour. Iron oxides tint the stone honey, orange and reddish, while copper and chromium compounds make it green.

It is important not to confuse onyx marble with the mineral onyx, a variety of chalcedony (quartz) used for jewellery. Chalcedony onyx is much harder but is rarely used in finishing; cladding slabs are carbonate onyx.

Exact characteristics depend on the deposit; visual selection is important for every onyx slab.

Translucency is what onyx is chosen for. Light transmission depends on several factors:

• Thickness. For backlighting, slabs are usually cut about 15–20 mm thick; thinner means more light but greater brittleness, so thin slabs are reinforced.

• Colour and density of the layers. Light honey and white grades transmit more light than dark green and brown ones.

• Surface finish. Polishing on both sides increases light transmission and depth.

• Type of lighting. Even lighting without hot spots is provided by LED panels or LED strip behind a diffuser. The distance from the light source to the stone is chosen so that individual diodes are not visible.

How to set up backlighting. The stone is installed with a gap in front of a light box. For walls and counters the light source is placed in a recess lined with reflective material. LEDs hardly heat the stone; a warm colour temperature brings out honey tones, a neutral one white and green tones. Access to the lights for maintenance is essential: a removable panel or an inspection hatch.

For large illuminated surfaces, composite panels are used: a thin layer of onyx bonded to clear glass or polycarbonate. They are lighter and stronger while keeping the glowing effect.

Where onyx is appropriate in interiors:

• Feature walls in halls, hotel lobbies and restaurants, backlit or not.

• Bar counters and reception desks with an illuminated front.

• Bathrooms: walls, vanity tops and panels, provided they are protected by impregnation and carefully maintained.

• Columns and partitions with internal lighting.

• Fireplace surrounds, decorative panels and tabletops in low-load areas.

• Lamps and small items: wall lights, floor lamps, furniture inlays.

Where onyx is not appropriate: on facades and in open-air spaces (it is sensitive to frost, rain and UV, and some grades fade); on high-traffic floors; on kitchen worktops, where acids and impacts are unavoidable.

Installing onyx requires care at every stage.

1. Layout. Every onyx slab has a unique pattern. Before cutting, the slabs are photographed and laid out on a wall elevation, book-matched or in sequence, so that the pattern continues.

2. Reinforcement. Brittle slabs are reinforced on the back with glass mesh in epoxy resin, or glass-backed composites are used. For backlighting the backing must be transparent.

3. Adhesive. Only white or clear natural stone adhesives: grey cement adhesive shows through and spoils the colour, and moisture from mortar can cause stains.

4. Fixing illuminated panels. Mechanical, on a frame with a gap to the light box, allowing the panel to be removed for lighting maintenance.

5. Joints. Minimal, filled with a clear compound or one tinted to match the stone.

At TECHNOFORMA, design, layout, 3D visualisation, measurements and installation of natural stone are carried out by the company’s own specialists; where necessary, the company also provides design supervision.

The care rules for onyx are the same as for marble, only stricter:

• after installation, apply a natural stone impregnation that protects against stains without reducing light transmission;

• clean with a soft cloth and pH-neutral products; no acids, chlorine-based or abrasive products;

• wipe up spilled drinks, cosmetics and water on tops immediately;

• do not place hot or heavy items on thin elements;

• scratches and loss of shine are removed by professional re-polishing.

With proper care onyx keeps its appearance in an interior for many years. The most common cause of problems is household chemicals not intended for natural stone.

For backlit panels, care also includes maintaining the lighting: every few years the LEDs and power supplies are checked and the diffuser is cleaned of dust. That is why access to the light box without removing the stone, or with removable panels, is planned at the design stage.

TECHNOFORMA’s completed projects are primarily facades, so the TECHNOFORMA projects section contains no examples of onyx interior cladding. Onyx is part of the company’s natural stone range alongside granite, basalt, dolomite, limestone, marble, sandstone, shell limestone and travertine. The company works with stone from India, Turkey, China and Iran and supplies it to order from around the world, and also provides design, 3D visualisation, layout, measurements, installation and design supervision.

If you are choosing stone for several tasks, both facade and interior, the overview “Comparing facade stone types: a table of properties” will be useful.