At a glance
| Colour family | Colourant the sources name, and what they say about repeating it |
|---|---|
| Clear (cristallo) | Purified raw materials, clarified with manganese dioxide. The silica is kept below 0.01% iron, because iron tints glass. |
| Amber and yellow | Modern list: cadmium sulphate, sulphur-carbon, uranium oxide or cerium oxide. Older list: sulphur for amber-yellow, silver for yellow, iron oxide for greenish-yellow. |
| Red, ruby and pink | Modern list for reds: gold, selenium, copper oxide or cadmium sulphate. Older list: gold for ruby red, silver and gold for pink. Gold ruby is called one of the most difficult colours to achieve (Corning Museum of Glass). |
| Violet and amethyst | Manganese (oxide). |
| Blue | Cobalt oxide or copper oxide (modern list). A cobalt-bearing product for blue-aquamarine (older list). |
| Green and turquoise | Chromium oxide or copper oxide (modern list). Copper oxide for blue-green (older list). |
| Opal white (lattimo) | A calcined lead and tin mixture or tin oxide gives the opaque white (glossary). Fluorite compounds are listed for milky-white opalescence. |
| Smoke and black | No colourant is named in the sources we read. |
| Aventurine (gold-flecked) | Tiny copper crystals that form as the glass cools. The museum says success is to a certain extent a matter of chance, which is where the name comes from. |
| Leaf and iridised effects | Not melt colour. Leaf is melted into the wall; iridised finishes are fumed onto the hot surface (our journal guide). |
From the Glass Museum Murano leaflet and the Corning Museum of Glass. These are colourants the sources record, not what our partner workshop uses. For colours not marked, the sources say nothing about repeatability. No colour tolerance is given: none was found published.
Where the colour comes from
Colour in Murano glass is made in the melt. The Glass Museum Murano (the Fondazione Musei Civici di Venezia) explains that coloured and opalescent glass is obtained by adding small quantities of other substances to the mix. Its modern list gives gold, selenium, copper oxide or cadmium sulphate for reds, cobalt oxide or copper oxide for blues, chromium oxide or copper oxide for greens, manganese oxide for violet and fluorite compounds for milky-white opalescence. The Corning Museum of Glass describes the same principle: coloured glass is made by adding small amounts of metal oxides to the batch.
Because the colourant is in the glass, it is not a coating that can wear off, and our Murano chandeliers page says the same. Surface effects are different. Our Murano techniques guide describes gold and silver leaf melted into the wall and iridised finishes fumed onto the hot surface, so ask whether an effect is in the melt or on the surface, and approve it on a sample.
The table gives the colourants the museum names, in its modern list (the leaflet's section on Murano glass today), its older list (the section on glass up to the nineteenth century) and its glossary. They are the substances the museum records, not a statement of what our partner workshop uses for any colour. Some of them contain cadmium, selenium or uranium. We have not researched which rules apply to products containing them or which the partner uses, so ask which colourant makes your colour, and whether any of the colourants are restricted where the fitting will be used.
Five reasons colour varies
No two hand-made pieces are identical, and colour is one of the first places it shows. The sources we read point to five causes. None of them is a defect: each is a reason to agree a limit before production.
| Cause | What the sources say | What to ask for |
|---|---|---|
| Separate melts | Each melt is its own, and the museum says coloured and opalescent glass is melted in smaller crucibles than clear glass. | One melt per colour, or the workshop lists what cannot be. |
| Heat history | Glass coloured with gold, or with uranium, changes colour when part of an object is reheated (the Corning Museum of Glass calls it striking). | Whether elements worked at different times can differ. |
| Wall thickness and technique | A thick wall, a layered sommerso wall and a thin free-blown wall do not read alike. In a clear, coloured glass a thicker wall generally looks deeper. | A sample in the technique and thickness you will use. |
| A difficult colour | Gold ruby (Corning Museum of Glass) and aventurine (museum) are the two the sources single out. | A trial piece, and the match limit for that colour in writing. |
| The light | The same glass reads differently unlit by day, lit at full output and dimmed, and under 2200 K or 4000 K. | Approve under the real lamp, lit and dimmed. |
The sources we read say which colours are hard. They do not say how far a hard colour will drift, and for the other colours we found nothing at all. Which colours cost more, or vary more, is therefore the workshop's call, and the reason to ask is the same each time: a colour that is hard to repeat is a colour to trial, and to approve before the programme clock starts.
How closely will pieces match?
We looked for a published tolerance for how closely one batch of coloured Murano glass matches another, or one element matches the next, and found none. That is not proof that none exists, but a figure in a brochure, or on this sheet, would be a guess. So the match limit is something you get from the workshop, for your colour and your technique, in writing. It can be expressed in three ways.
- In words, to the eye. For example: elements of one colour are indistinguishable when seen side by side with the control piece, lit, from a stated distance. Most projects will use this.
- As a measured colour difference. A colourimetry method exists: ISO/CIE 11664-6:2022 specifies how to calculate a colour difference (the CIEDE2000 formula) between two colours perceived as coming from reflecting or transmitting objects. It gives the formula, not a pass mark, so the limit has to be agreed. How well a measurement works on thick, curved, hand-blown glass, and what limit suits it, we have not checked. Treat it as an option to discuss with the workshop, not a requirement.
- By what is held constant. One melt per colour, the same technique and wall thickness as the sample, and the sample approved under the real lamp. This is where most of the control is.
Reference systems. Our Murano chandeliers page says colour can be matched to Pantone or RAL references. Systems such as RAL and NCS describe surface colours (see our sheet on RAL, BS 4800 and NCS colour references), while glass colour is seen through the wall and changes with thickness and light. Use a reference number as the target the workshop proposes a sample against. The signed sample, not the number, is the standard.
Colour through light
Glass changes character with the light, and there are three conditions to approve it in: unlit in daylight, lit at full output, and fully dimmed. Many LED sources do not warm as they dim, unless they are dim-to-warm, which is why a colour approved lit at full output cannot be assumed at the lowest level (see colour temperature by space and dimming protocols). Check each of them, with the lamp that will be fitted.
| Glass | What it does to the light | What to check |
|---|---|---|
| Clear | Shows the lamp and its colour. | Look at the lamp itself, not only the glass. |
| Coloured, transparent | Tints the light that passes through it, and absorbs some. | Ask for the light output with the glass fitted, not the bare lamp. |
| Opal white (lattimo) | Our journal guide says it diffuses the lamp, so the source is hidden. It also holds some light back. | The lighting designer allows for the light it holds back. |
| Smoke and black | Absorbs more of the light. | Check the output and the look when lit. |
| Aventurine | The flecks catch the light and throw back a glitter (our journal guide). | View it lit; the flecks change with the angle. |
| Iridised and leafed | Iridised finishes take a lustre that shifts as you move round the piece (our journal guide). Leaf breaks into a veil. | Approve on a sample, from several viewpoints. |
The drawing shows the direction of the effect for seven notional colours under daylight and four warm to neutral lights. Warm light favours reds and ambers, dulls and darkens blues and violets, and turns an opal white cream. It is a simple model, not a prediction for real glass.
Sign off colour against a sample
Sampling is one of the two moments in our sampling process: option samples in design development, then control samples at specification freeze, the exact finish that production will be measured against. For glass the same idea needs three additions: the sample is made in the technique and thickness of the real element, it is judged lit, and the match limit is written down. The steps below fit the general approach in our sheet on sample hierarchy and approval.
The sign-off sheet below is what turns the sample into a record. Keep it with the drawing, and make it part of the order. A colour change after signature is a variation: the glass is made again, and the programme moves with it. Murano glass is blown to order on the furnace schedule, and our lead times page counts the programme from written approval of the shop drawings and samples, so settle colour before that point.
| Field on the sign-off sheet | What to record |
|---|---|
| Sample reference and date | A number on the sample, on the drawing and in the order. |
| Technique and wall thickness | For example free-blown, or sommerso, and the range of wall thickness the workshop states. |
| Colour family and colourant | As the workshop states them, and whether the colour is in the melt or on the surface. |
| Light used to approve it | Lamp type, colour temperature and level; also unlit, in daylight. |
| Photographs | Taken lit and unlit, beside the control piece, with a neutral background. |
| Match limit | The limit the workshop works to for this colour, in its own words, or as a measured colour difference. |
| Melt statement | Whether all elements of one colour come from one melt, and which cannot. |
| Control pieces | How many, who holds each, and how it is identified and stored. |
| Remake rule | What happens to an element outside the limit: who remakes it, by when, and what it does to the programme. |
| Signatures | The named decision-maker for the project and the workshop, with the date. |
Specification wording
Paste into your schedule or specification and replace anything in [square brackets] with your own figures. Wording is a starting point: your specification governs.
Colour of [element type] to match the approved sample [ref], made in [free-blown / sommerso / incalmo] glass at the wall thickness stated by the workshop [ ] mm, signed by [designer] and [workshop] on [date]. Each party keeps a control piece, identified [ref]. The signed sample is the standard. Any colour reference quoted (for example RAL or NCS) is the target for the sample only.
Colour to be assessed unlit in daylight, lit at full output and fully dimmed, with the specified lamp fitted [type, [2700] K], side by side with the control piece at a distance of [1.5] m, by [named person] in person, not from photographs or a screen.
All elements of one colour to be made from one melt [for the whole order]. Where the workshop cannot do this, it states so before approval, lists the elements affected and says how they will be matched.
The workshop states in writing, before approval, the colour-matching limit it works to for [colour]: [in words, for example indistinguishable to the eye beside the control piece, lit, at [1.5] m / as a colour difference of not more than [ ] by CIEDE2000, with the instrument, illuminant and geometry stated]. The limit forms part of the order.
An element outside the agreed limit is remade by [workshop / at the workshop's cost] within [ ] weeks of written notice, and the effect on the programme is stated in writing at the same time. A colour change requested after signature is a variation to the order.
Terms used on this page
- Colourant
- A substance, usually a metal compound, added in small amounts to the batch to colour the glass all the way through.
- Melt
- The batch of glass melted in one crucible at one time. Elements made from different melts can differ slightly in colour.
- Control piece
- A signed sample that each party keeps. Any dispute about colour is settled against it, lit, under the conditions agreed.
- Strike
- The change of colour in heat-sensitive glass, such as glass coloured with gold, when part of an object is reheated.
- Colour difference (delta E)
- A single number for how far apart two colours are. The CIEDE2000 formula in ISO/CIE 11664-6 is one way to calculate it. It does not say what difference is acceptable.
Standards and sources
- Fondazione Musei Civici di Venezia, Glass Museum Murano: What is glass? (English leaflet): read 5 Nov 2026: pages 3 and 4 (modern kiln, colouring), 6 (older colouring agents), 9 and 10 (glossary). Undated leaflet.
- Corning Museum of Glass, library guide: Colour (videos): read 5 Nov 2026: metal oxides, gold ruby, heat-sensitive glass.
- ISO/CIE 11664-6:2022, Colorimetry, CIEDE2000 colour-difference formula: listing read, scope only; the standard text was not read.
- Make Bespoke Studio: Murano techniques guide: leaf, iridised, aventurine and lattimo descriptions.
Questions we are asked
How do Murano glass colours get their colour?
A small amount of a colourant, usually a metal compound, is added to the melt, so the colour runs through the glass. The Glass Museum Murano lists, for example, cobalt oxide or copper oxide for blues, gold, selenium or copper oxide for reds and chromium oxide or copper oxide for greens. Which colourant the partner workshop uses for a colour is for the workshop to say.
Can Murano glass colour be matched exactly?
Not exactly. The glass is hand-made and coloured in the melt, and we found no published tolerance for colour match between batches or elements. Approve a physical sample in the real technique and thickness, keep a signed control piece, ask for one melt per colour, and get the workshop's match limit in writing.
Will the colour look different when the fitting is lit?
Yes, and it will differ between full output and dimmed. Approve the sample unlit in daylight, lit at full output and fully dimmed, with the lamp that will be fitted. Many LED sources do not warm as they dim, so full-output appearance cannot be assumed at the lowest level.
Can I specify Murano glass colour by RAL or Pantone?
Our Murano chandeliers page says colour can be matched to Pantone or RAL references, but those systems describe surface colours and glass colour is seen through the wall. Use the number as the target for a sample, and make the signed sample, not the number, the standard.
Which Murano glass colours are hardest to repeat?
The two the sources we read single out are gold ruby, which the Corning Museum of Glass calls one of the most difficult colours to achieve, and aventurine, where the Glass Museum Murano says success is to a certain extent a matter of chance. For other colours we found no statement either way, so ask the workshop.
What is a control piece?
A sample that both sides sign and each keeps. If a delivered element looks different, it is compared with the control piece, lit, under the conditions agreed at sign-off. It turns a matter of opinion into a comparison with one agreed object.
Download the factsheet
A two-page A4 PDF with the palette by colourant, why colour varies, the sign-off steps and paste-in wording, to keep with your project file.