Spun roundels windows

The origin of spun roundels windows is very ancient. During the late medieval period, all the glass was produced by blowing and it was not possible to create a glass sheet large enough to close an entire window. So as an alternative to quarries, diamond and rectangles, spun roundels were also used to create glass mosaics, which would be capable of stopping the cold and allowing the light to filter into the buildings.
Spun roundel windows are very characteristic of Venice. It is here we find spun roundel windows in almost all  of the churches and in many historic buildings in Serenissima. It is for this reason spun roundels are called Venetian roundels.

Spun roundel arrangement in stained glass windows

Spun roundels can be elegantly inserted in any glass project including geometric and classic forms, and they can also be interesting inserts for modern and contemporary stained glass. Here are some examples of stained glass in Venice where spun roundels are found. The most traditional solutions lead us to three types of spun roundels glazing, aligned, slanting or infrequent aligned roundels.

In the aligned arrangements, the roundels are arranged horizontally and vertically with tangent circumferences. The space between one roundel and the next will be a four-pointed star that can be carefully cut with a glass of your choice.

In slanting spun roundels windows, the roundels are arranged on oblique lines generally at 45 ° and the space to be filled between roundels will be a three-pointed star. At the edge of the window, we have to cut the roundels in half which is quite complicated due to the considerable thickness of the glass in the centre of the roundel itself.

Infrequent roundels windows are a solution if you want to create an elegant spun roundel window at an accessible price. The roundels are spaced and there will be more space for the background glass or any different colour border.

Aligned Roundel Stained glass window
Aligned Roundels
Slanted Roundel Stained Glass window
Slanted Roundesl
Spaced Roundels
Spaced Roundels


Spun roundels of various sizes can be found on the market . Once the project has been planned, the roundels must be cut or ground to size. In the Middle Ages the same production technique for spun roundels was used to produce sheets of glass that would then be cut into smaller pieces. This type of glass was called crown glass.


Spun roundels are usually produced light colours as they need to allow light into the building. Later, when master craftsmen thought of using the roundels as a decorative element for stained glass windows, they started being produced in more intense colours.  Today, due to their high production costs, the colours available on the market are somewhat limited.


Being a handmade product, the thickness  is variable, the central part is thicker and has a more intense colour, and as the roundel tapers to the edges, it becomes progressively thinner and thus the colour is less intense.

A spun roundel is a particular circular glass tile that is created during the blowing process by opening a sphere of molten glass with centrifugal force. Its main features are concentric streaks that can be fully appreciated when it is lit from behind. The central top of the roundel, the nipple, is where the blowing barrel was attached during the roundel’s production.

The term bulls-eye or glass bottoms are synonyms for roundels.

Coloured Roundels

IKO Studio is at your service should you wish to commission a window with or without glass roundels. IKO Studio collaborates with other professional craftsmen and women in Murano to obtain the highest quality, mouth-blown roundels for your Venezian style window.

Beware of imitations

This type of glass is often confused with spun roundels windows, but the differences are remarkable. First of all, this is made from a single sheet of glass and not a glass mosaic assembled with lead. Secondly, this type of glass is an industrial product and has been printed and does not have the same transparency characteristics of real mouth-blown roundels.  True spun roundels windows are very elegant and are the ones that give the greatest touch of antiquity to an environment. Their transparency and concentric streaks offer excellent lighting and beauty but at the same offer a good level of privacy.

Circle Glass