Sub-surface engraving is still not very widespread and is a sensational kind of laser processing of glass. That is partly due to the fascinating options of 2 and 3-dimensional design inside the glass and the possibility of importing photographic motifs with nuanced shading.
It is also due to the fact that the surface of the glass itself is completely untouched by the laser finishing. Visible structures only appear inside the glass. Every single laser pulse creates a 100 micrometre-sized dot in the glass, which the eye detects as a tiny opacity.
Any kind of 2 or 3-dimenstional motif can be created inside the glass out of lots of these tiny dots. Normally a distance of about 1mm from the surface of the glass must be kept so that the stability of the glass is not impaired.
The prerequisite for sub-surface engraving of glass is that the surface through which the laser beam enters into the material must be of good optical quality. Frosted or patterned glass surfaces are out of the question for this reason.
If the glass is only frosted or patterned on one side you can of course still work from the clear or smooth side of the glass. Safety glass or thermally toughened glass or glass which is to be processed into safety or thermally toughened glass can unfortunately not be provided with sub-surface engraving.
From experience, the micro-structures created by the laser can lead to a sudden and spontaneous breakage of the glass even months later although the safety or toughened glass looks stable initially.
Where there are stricter safety and stability requirements, such as fully glazed doors, façade elements or shower cubicles, laminated glass made from float glass can often be used as an alternative, perhaps in combination with toughened glass.
In this way sub-surface laser engraving can also be used where otherwise it would not be an option because of the use of safety or toughened glass.
Normal or low-iron float glass (e.g. optiwhite® or starfire®), even if it is a component of a laminated glass, can easily have sub-surface laser engraving. At Cerion insulated laminated glass with thicknesses of over 50mm has already been sub-surface engraved.
Sub-surface engraving with amazingly good engraving quality has been achieved at Cerion even with material thicknesses of about 200mm through 10 optiwhite plates each 19mm thick. Care must be taken to ensure that the laser beam does not focus onto the intermediate layers of PVB or EVA film or cast resin.
Otherwise this can cause blisters to form as well as unpleasant discolouration due to the material burning. Insulated laminated glass can therefore not simply be structured throughout its whole thickness with the laser - on the contrary, the construction and thickness of the individual glass and film layers must be taken into consideration very accurately.
In laminated glass a distance of the sub-surface engraving from the surface of the glass of approx. 1mm must be adhered to even on the internal layers of glass bordering onto the organic intermediate layers, in order to guarantee the stability of the glass here too.
Individual panes of glass, which have already been provided with sub-surface engraving, can easily be processed into laminated glass later on. Many other types of glass such as borosilicate or crystal glass, quartz glass and optical glass can normally be sub-surface engraved easily with a laser.
Dark and colourless glass ceramic has also been structured successfully using Cerion sub-surface engraving systems. Even transparent plastics such as PMMA, polycarbonate, polyamide or PET - to name just a few - can be sub-surface engraved with a Cerion laser.