The word 'glass' is an all encompassing name given to materials that can have significant variations in chemical and other properties.

1. Laser Marking and Engraving Glass
The word ‘glass’ is an all encompassing
name given to materials that can have
significant variations in chemical and other
properties, however, it is most commonly
used to describe various forms of silica
based transparent materials that are often
quite fragile in nature such as spectacles,
drinking vessels, vases, etc.
Aside from the chemical differences in
many forms of glass, variations in process of manufacture
contribute towards making glass a material that is somewhat
wide in scope and inconsistent in make-up. Even glass of the
same make-up and shape can vary in size due to thermal
inconsistencies during the cooling process, therefore, unlike most
other materials glass can be difficult to laser engrave with a
highly consistent effect.
At shorter laser wavelengths glass is generally transparent,
allowing the beam to pass through. For example, the lower layer
of a 1µm f-theta lens found in a laser marking machine is made
from glass. However, with a specially configured 532nm green
laser it is possible to mark some forms of glass within the material
itself to create some stunning effects.
For surface laser marking glass the 10.6µm laser wavelength is
most suitable.
When marked by laser glass will not vaporise. When exposed to a
10.6µm laser, glass thermally reacts and micro cracks are formed.
During the laser marking process it’s very important not to
thermally overload the material as the desired micro cracks will
form into larger material fractures that will flake away from the
main body of the material causing an undesirable effect. To
minimise this risk, techniques like marking through wetted
newspaper or marking through dish soap are often used where
this surface applied additive acts as a heat-sink to minimise any
thermal overload to the glass itself. Use of such additives can
however significantly reduce throughput.
Aside from the laser wavelength the optical configuration of
the laser engraving machine has the biggest influence on how

2. glass appears after it is laser engraved. The focal point of a galvo
laser can be as many as x5 the size of a typical plotter laser.
Therefore, marking hatch filled designs is best performed by a
plotter laser. When using a galvo laser the best results are
created by only marking vector lines.
The plano convex lens of the plotter format laser engraving
machine provides for the smallest possible focal point, as small as
90µm, which delivers a high energy density and a very locallised
thermal reaction the result of which is a mark closest to
resembling that of chemical etching or sand blasting. This type of
machine is best used for marking higher value items such as
presentation awards, for example.
However, laser engraving glass with a plotter laser can be a very
slow process, often taking minutes to produce.
For more industrial applications a galvo laser is often the only
system that can be used because it will create a mark in mere
seconds. Actually, for simple marking applications like laser
marking wine glasses with volume fill lines a galvo laser can
produce a mark well under a single second, so fast that the mark
will appear after the laser has finished; much the same way that
the sound of thunder can follow the flash of lightening.
Today, most plate glass for fenestration is marked by a 10.6µm
galvo laser and whole new processes such a nucleation of beer
glasses can only be produced with this type of laser marking
machine because aside from the rapid marking speed a very long
focal length is required for the laser to reach into the bottom of
the glass.
At Lotus Laser Systems we manufacture a wide range of laser
marking, laser engraving and laser cutting machines. Our experts
would be happy to recommend which configuration best suits
your application.
Source: http://lotuslaser.blogspot.com/2016/03/laser-marking-
and-engraving-glass.html