The onyx never touches the water
This surprises almost everyone. The water is held by a freestanding 316 stainless body with its own insulation and pipework. The onyx sits outside that body, separated by a 25-millimetre cavity containing the lighting. There are two reasons. Onyx is a banded stone that splits along its layers, and onyx kept permanently wet changes colour as the iron minerals in its bands oxidise. A tub whose water touches the stone directly ages unevenly within two years, and unevenly is the worst way for a feature piece to age.
So this is really two products married together: a stainless body built to the same specification as our 316 stainless ice bath, and a glowing onyx enclosure around it. It also means the tub can be serviced like any other steel tub, which matters in a hotel.
Lamination to glass, and why it cannot be skipped
An 18-millimetre onyx slab standing free will break if a trolley catches it or if the building moves. Every slab is bonded to 6-millimetre low-iron glass with a clear epoxy resin whose refractive index is close to that of glass, cured in a vacuum chamber to pull out the bubbles. A bubble one millimetre across becomes a bright dot the moment the light behind it comes on. The result stays translucent but has roughly four times the flexural strength, and if it ever does break, the pieces stay attached to the glass instead of landing in the room.
Light transmission, 18 mm onyxabout 12 per cent
Laminating glass6 mm, low iron
Adhesiveclear epoxy, vacuum cured
Strength gainroughly four times in bending
LED to slab distance25 mm, below that the dots show
Colour temperature3,000 K, CRI above 90
Lamp heat into the waternone, the cavity vents outward
Why the cavity is exactly 25 millimetres
LED tape emits from points 16 millimetres apart. Pressed too close behind the stone, that row of bright points reads through the onyx like a string of beads. Twenty-five millimetres with a white diffuser at the base of the cavity lets the light blend before it reaches the stone, and what you see is an even glow. We test this slab by slab, because heavily banded onyx needs 30 millimetres while a clear stone is fine at 20. The cavity also vents outward, so the 48 to 84 watts of lamp heat warms your room rather than the water.
Choosing the block is the part that takes the time
Onyx is sold by the block and no two blocks are alike. A 400-litre tub needs about 4.2 square metres of slab whose veins run continuously across four faces, and that means a whole block rather than remnants. You choose from photographs of the block already sawn open, then we chalk the slab sequence before cutting. The process takes three to four weeks and roughly 40 per cent of the material leaves as corner offcuts, which is the single largest reason onyx sits so far above marble in price.
| Onyx colour | How it glows | Block availability | Note |
|---|
| Honey | warm yellow, strong brown veining | easiest | the most-chosen stone |
| Jade green | soft green with white veins | moderate | thick banding, needs a 30 mm cavity |
| Milk white | even cream | difficult | most expensive, finest veining |
| Brick red | deep orange | seasonal | changes most when the light is off |
When onyx is the wrong choiceOnyx must not go outdoors. Ultraviolet bleaches the coloured banding within two to three years and rain dissolves minerals out of the pores, leaving permanent pale streaks. It is also wrong for a busy thoroughfare: the slab corner at knee height is what gets knocked, and although the glass lamination holds it together, a crack still shows because light passes through it. For luxury stone that tolerates anything, a marble ice bath or granite is a far quieter thing to own.
Price, and where the money actually goes
The range is Rp 85-150 million for 300 to 600 litres. Roughly 55 per cent of that is stone and waste, 20 per cent the stainless body inside, 10 per cent lamination and lighting, and the balance fabrication and installation. The chiller is separate as with every other tub: 1.5 PK for 400 litres in hot lowland, checked on the chiller calculator. If the tub is the centrepiece of a spa you are building, it is usually cheaper to fold it into a custom wellness area than to order it alone, and every component price is on the pricing page.
Two days on site, and not one cut made there
All the cutting is finished in the workshop. On site we only assemble, and that is a requirement rather than a preference: cutting onyx indoors means fine stone dust across a finished room, and any cut made without a proper bed multiplies the risk of cracking a slab worth millions. So the order of work is inverted from normal stone fitting. We measure the room to three millimetres before production, build a support frame adjustable at six points, and the slabs arrive already numbered in sequence.
Day one is the stainless body, pipework, frame and LED tape. Day two is fitting slabs from the bottom up, adjusting the cavity depth face by face until the glow is even. The final adjustment is always made with the room lights off, because that is the condition in which you will actually look at it. We ask one thing from the owner: put the tub lighting on its own switch. Backlit onyx only reads as onyx when everything else is dark.
Does the lighting warm the water?
No. The lamp cavity sits outside the insulated stainless body and vents into the room, so those 48 to 84 watts heat your air-conditioning bill rather than the tub. The water-side heat load is identical to a plain stainless tub of the same volume.
Can the light colour be changed?
We fit warm white at 3,000 K because it is the colour that makes honey and green onyx look like themselves. RGB tape can be fitted on request, but coloured onyx lit blue or violet loses its veining completely and reads as plastic — we will say so before we install it.
If one slab breaks, does the whole tub have to be redone?
No, but a replacement slab from a different block will not match. That is why we keep one spare slab from your own block for every onyx tub we deliver, stored in Tabanan for five years at no charge.
Can it be built without the backlighting?
Yes, and it takes about Rp 9 million off the price. But unlit onyx looks like expensive cream marble, so if budget is the driver, marble gives a very similar look for far less.
How long does the whole thing take?
Three to four weeks, plus block waiting time if your colour is out of stock. Installation is two days because slabs go on one at a time with re-measurement, and we never cut onyx on site.
