How is vitreous enamel made? 

We are the UK’s largest vitreous enamel supplier, manufacturing the majority of cladding and enamel signage for TfL’s London Underground. In this blog, we will take you through the process of making a vitreous enamel street sign. 

Read on to learn about each stage of the process!

The vitreous enamel process starts with small pieces of glass called frit. This base enamel material is then mixed with a carefully selected amount of coloured oxide (pigment) compounds and water. Varying the combination of both ink and catalyst allows the team to achieve a range of matt, satin and gloss finishes.

Milling the enamel

A rotating barrel containing heavy ceramic balls is then filled with the carefully weighed materials. This rotates very fast and grinds the mixture, spinning until the enamel materials reach a liquid state. 

Metal fabrication

Low-carbon sheet steel is used as the base metal substrate. It is versatile, heat resistant and suitable for a wide range of uses. Panels are formed to the shapes and sizes required to a tolerance of +/-2mm. Flanges are formed by folding to an outside radius of 3mm. The steel conforms to the requirements of BS EN 10209.

Spraying enamel

After rinsing and neutralising the metal sheet, an enamel ground coat is evenly applied by a spray gun by one of our skilled team. This has allowed a number of unique finishes to be developed over time including our popular Nori textured finish below.

Firing the enamel

The substrate with its ground coat is then fired in the furnace at 830 degrees Celsius (1500 degrees Fahrenheit), fusing the vitreous enamel to the metal base.

Screen printing

Once cooled, screen printing can start. Firstly, a mesh screen is stretched over a frame and coated with a light-sensitive emulsion. Once dry a digital negative can be used to create an exposure of the artwork. This is then jet-washed in water and gaps in the emulsion are left where the negative/image was placed.

A squeegee or blade can then be used to pass ink over the gaps in the screen which applies a print onto the substrate’s (vitreous enamel) surface. Artwork consisting of multiple colours are built up in layers, having to be processed one after the other.

Firing for a second time

Firing for a second time at 760 degrees Celsius (1400 degrees Fahrenheit) adheres graphics & text permanently to the substrate. A key benefit of vitreous enamel is that it is colourfast meaning colours, graphics and text are ‘locked in’ and are protected from UV damage. This means vitreous enamel signage can look as good as new, for decades.

The result

We have been the principal supplier of the London Underground’s, vitreous enamel signage and cladding since the 1990s. Vitreous Enamel was selected to replace combustible materials throughout the London Underground after the tragic King’s Cross fire in 1987. Vitreous enamel is fire-resistant, graffiti-resistant and highly durable, making it the perfect material for TfL’s famous signs, maps and cladding.