Coloured through or coated: the difference shows in year three, not in the showroom

Materials and finishes

Two fittings that look identical can have opposite futures. The difference is not in the list price: it is in where the colour sits, and it can only be read on a cut edge.

Two ways to make amber glass

The first puts metal oxides into the molten batch, before the glass takes shape: the colour is the glass, not a layer on top of the glass. The second takes clear glass and deposits a lacquer or a film on it, achieving the same amber at a fraction of the cost and with far higher repeatability.

In a showroom, with the fitting switched off and half a metre away, the difference cannot be seen. With the fitting lit it starts to show: glass coloured through has a depth that changes with thickness, so the colour is more intense where the piece is thicker and softer where it thins out. The coated one is uniform, because the layer has the same thickness everywhere, and that very uniformity is what makes it recognisable to anyone who knows how to look.

The edge tells you everything in two seconds

There is a test anyone can run and no catalogue can get around: look at the edge. On glass coloured through, the cut is the same colour as the surface, because it is the same material all the way in. On a coated one the edge is clear or white, and you can see the line where the layer stops.

That is why it is worth asking for a physical sample and not a photograph. A photo has no edges to look at, nor does a render, and a datasheet saying «amber glass» does not distinguish the two. The sample distinguishes them in two seconds, with no argument and without having to take anybody's word.

What happens over ten years

Glass coloured through does not change: the oxides sit inside the structure, there are no layers to lose, and the colour it has today is the colour it will have in twenty years. It is why medieval church windows still hold their colour, and it is an argument that sounds rhetorical until you look at a supply delivered eight years ago.

A lacquer layer, by contrast, ages, and it ages for three reasons a hotel has all of: the heat of the LED sitting centimetres away, ultraviolet where there is daylight, and cleaning products. The first sign is not that the colour fades everywhere: it is that it fades where the fitting runs hottest, so unevenly, and unevenness is noticed long before fading. It is a fault that is hard to contest, because it arrives once the warranty has expired and looks like normal wear rather than a choice of material.

The five points where the difference is paid for

None of these is visible on delivery, and that is exactly the problem: the choice is made at a moment when the two options look equivalent, and it is paid for at a moment when they no longer are:

• replacing a broken piece, which on an eight-year-old coated glass does not match its neighbours
• cleaning, which takes a little colour off a lacquer every time and takes nothing off glass coloured through
• the heat of the LED, which on a coated piece produces a pale halo directly above the source
• extending the property, when pieces identical to those bought years earlier are needed
• sunlight through a window, which bleaches a layer and does not touch a colour in the mass

The real problem is not the colour: it is the batch

On a supply of a hundred and twenty fittings the risk is not that the colour is wrong: it is that it is different from one piece to the next. Glass coloured through has a natural variability between melts, and that variability is real and has to be declared, not hidden: two different melts give two slightly different ambers.

A serious supplier manages it in one way only: they produce the whole supply from the same melt and set aside a small surplus for future replacements. A supplier who never mentions it has either never faced the problem or is selling you a coated glass, which does not have that problem because lacquer is industrial and repeatable.

The surplus is the most underrated part

In a hospitality property something always breaks: a trolley, a ladder, a hurried clean, furniture being moved. If the replacement piece comes from a different melt or a different coating batch, it shows — and it shows more when it sits beside the originals, because the eye compares the neighbour and not a memory.

This is why on an important supply the surplus is not a commercial courtesy: it is part of the supply, and how much it is and where it is kept has to be written down. Five per cent on a decorative supply is a reasonable rule; on a one-off piece the reasoning changes, because there the spare does not exist and what is kept are the drawings and the melt data.

The questions to put to the supplier

There are four, and the first is not about price. They are asked with the sample in hand, because on a sample the answers are verified at once instead of remaining promises:

• is the colour in the mass or on the surface: show me the edge of a cut piece
• does the whole supply come from one melt, and with what tolerance between pieces
• how much surplus is foreseen, where it is kept and for how many years
• if a piece were needed in eight years, how is it reproduced and with what colour deviation

When coated is the right choice

It is not always the worse choice, and saying otherwise would be selling rather than advising. Coated costs less, is far more repeatable between pieces, and allows colours that do not exist in the mass or would cost as much as a car. On a numerous supply in a colour outside the palette, it is often the only workable route.

It makes sense where the piece sits far from the heat source, where it takes no direct sun, where cleaning is gentle, and where the expected life is short — a seasonal installation, a venue refurbished every five years. The fault is not choosing coated: it is choosing it while believing you are buying the other.

The cost being compared is the wrong one

The comparison almost everybody makes is between the two list prices, and on that comparison coated always wins. The honest comparison is between the list price and the sum of what happens afterwards: replacements that do not match, the moment the room has to be redone because the pieces no longer look alike, and the devaluation of a room that looks tired before its time.

It is not a calculation that can be done in the abstract, because it depends on the property and on how long it is expected to last. But it has to be done, and done early: it is the only way for the initial price difference to stop being the only number on the table. Whoever runs the property already does that calculation: they do it every time they have to explain to an owner why a room looks old sooner than expected.

How it is written into a specification

«Amber glass» is not a specification: it describes both things and binds neither. The wording that binds names where the colour sits and how it is verified, and it needs no technical skill to be checked — anyone can look at an edge.

It is worth adding two lines on behaviour over time: that the colour must not vary perceptibly after a stated number of operating hours, and that the supplier guarantees the reproducibility of the colour for a declared period. These are undertakings a serious supplier gives gladly, because they set them apart.

Mouth-blown is yet another thing

Coloured through and mouth-blown are not synonyms: you can have glass coloured through made industrially, and clear mouth-blown glass. When the two come together, the piece has a quality no industrial process reproduces: the thickness varies slightly, so the colour breathes along the surface.

That is exactly what makes a handmade chandelier recognisable in a photograph, and also what makes it hard to specify: two blown pieces are not identical by definition. The line between a variation that is a virtue and one that is a defect is drawn by inspection in production, and it has to be agreed beforehand with declared limits, not left to the taste of whoever receives the goods.

How we handle it

On bespoke pieces we always say which of the two routes we are proposing and why, including when we propose the coated one — especially when we propose the coated one. A client who knows what they are buying comes back; a client who discovers in year three that they bought something else does not come back, and they are right.

And for numerous supplies we put the melt and the surplus in writing in the order confirmation, not in the quotation: in a quotation it is a promise, in an order confirmation it is an undertaking that survives after everyone who spoke on the phone has changed role.

• A bespoke piece
• The properties we have lit
• Free lighting calculation
• Expert advice