Key points
- Cobalt blue glass is glass colored deep blue with cobalt, added to the batch when the glass is made. The color runs through the glass rather than sitting on its surface.
- Other bottle colors come from other additives: iron and sulfur give amber and brown, and iron alone can give green.
- Cobalt blue has a long history, from ancient Egypt to the "Bristol Blue" glass made in Bristol from the 1700s.
- Recycle Now, the UK recycling guidance site, says glass bottles of any color can be recycled, and that at bottle banks blue glass goes in with green glass.
What is cobalt blue glass? It is glass that has been colored a deep blue by adding cobalt, for example as cobalt oxide, when the glass is made. Because the colorant is dissolved into the glass itself, the blue runs all the way through. Amber glass gets its color a different way, from iron and sulfur. This guide explains how bottle colors are made, where cobalt blue comes from and how colored glass is recycled in the UK.
How glass gets its color
Recycle Now lists the four main ingredients of new glass as sand, soda ash, limestone and other additives for color or special treatments. The color comes from those additives.
The Corning Museum of Glass explains that one way of coloring glass is to use a dissolved metallic oxide, which gives color throughout the glass, and it names the colors that common additives produce:
| Glass color | Additive named by the Corning Museum of Glass |
|---|---|
| Very dark blue (cobalt blue) | Cobalt |
| Light blue | Copper |
| Green | Iron |
| Amber and brown | Iron and sulfur |
| Amethyst | Manganese |
So "cobalt blue", "amber" and "green" describe what went into the glass, not a coating or a label. A clear bottle and a cobalt bottle can have the same shape and size. The difference is in the recipe.
A short history of cobalt blue glass
Cobalt has colored glass for thousands of years. The Royal Society of Chemistry notes that cobalt salts have been used for centuries to produce blue in paint, porcelain, glass, pottery and enamels. It also records that the tomb of the pharaoh Tutankhamen held a small glass object colored deep blue with cobalt.
Bristol Blue
The best-known British example is Bristol Blue glass. Bristol Museums says the opportunity to make cobalt-blue glassware arose in Bristol at some point in the mid to late 1700s, and that it is not clear exactly when.
The museum describes one theory for the name. William Cookworthy, a pharmacist and china manufacturer in the South West of England, imported high quality cobalt oxide from Silesia to decorate his porcelain. If, as the theory goes, he shipped it into England through the port of Bristol, the city's glassmakers had the best access to it. The museum adds that cobalt oxide added to lead glass produces "a deep, rich, distinctive blue".
Cobalt blue and amber bottles compared
The differences you can check for yourself are simple:
- Color source: cobalt gives very dark blue; iron and sulfur give ambers and browns.
- Where the color sits: in both cases the colorant is in the glass itself, not painted on.
- Recycling: Recycle Now says glass bottles of any color can be recycled, and that at bottle banks blue glass goes in with green.
You will often read that one color is "better" than another for what is inside. This guide does not rank the colors, and it gives no figures for how much light each one filters, because we did not find an independent source we could check. A bottle's color tells you what the glass contains, not how a particular product inside it will behave.
Recycling colored glass in the UK
This section is general guidance from Recycle Now about glass bottles and jars. It is not a statement about any particular product's packaging, ours included.
Recycle Now says glass bottles of any color can be recycled, along with food jars and non-food bottles such as perfume and aftershave bottles. Most local authorities collect glass bottles and jars from homes, and they can also be taken to bottle banks. The Recycle Now site has a postcode search for checking what your council collects.
How to prepare glass for recycling
Recycle Now's advice for glass bottles and jars is:
- Empty and give a quick rinse, because leftover liquid can contaminate other recyclables.
- Put lids and caps back on, so they are not lost during sorting and can be recycled separately.
- Remove corks.
- At bottle banks, put blue glass in with green glass.
Rules differ between councils, and packaging often has parts made of more than one material. Check your council's guidance for the pack in front of you.
What cannot go in with bottles and jars
Recycle Now lists items that cannot be recycled with glass bottles and jars: ceramics such as crockery, drinking glasses, glass cookware such as Pyrex, light bulbs and tubes, and vases.
What happens next
Recycle Now says glass is 100% recyclable and can be recycled endlessly with no loss of quality. Collected glass is color sorted if required, crushed, cleaned of contaminants, mixed with raw materials, melted and then molded or blown into new bottles and jars. For the formats supplements come in, from capsules to drops, see Liposomal NAD+ and Other Formats, Explained.
Our bottle
NAD+ Sublingual Drops come in a cobalt glass bottle with a black dropper cap. We do not claim that the color of the glass does anything for what is inside, and nothing in this guide is a statement about how our packaging should be disposed of. For what NAD+ is as a molecule, see the science page, and for what the words "food supplement" on a label mean, read What Is a Food Supplement? The UK Definition.
Frequently asked questions
What makes cobalt glass blue?
Cobalt, added while the glass is made. The Corning Museum of Glass lists cobalt as the additive that produces very dark blue glass, and Bristol Museums notes that cobalt oxide added to lead glass gives a deep blue.
Is cobalt blue glass better than amber glass?
This guide does not rank them. The two colors come from different additives and look different. We did not find an independent source we could check on how their light filtering compares, so we give no figures.
Can blue glass be recycled in the UK?
Yes. Recycle Now says glass bottles of any color can be recycled, and that at bottle banks blue glass goes in with green glass. Check your council's rules for home collections.
