Pro Quality Laser Engraving of Glass & Crystal
Expanding into glass and crystal engraving with your laser is a great way to increase your engraving sales and find your way into new markets. Applications exist for both decorative and industrial glassware and they are constantly growing.
Glass and crystal encompass a wide variety of products and there are many different techniques for engraving these materials. These laser engraving techniques have been developed over the last 20 years for these materials and some are more practical than others. The best techniques are always the simplest ones. Simple processes can easily be recreated in a production environment and ultimately lead to higher productivity.
How it Works
Laser engraving on glass and crystal will become a lot easier once you understand the principle of how the laser works with these materials. We know that the laser engraver produces focused heat energy and it is this heat that micro fractures or chips the top surface of the material. The beam is absorbed by the glass or crystal and the top surface heats and fractures. The result is an etched look that that can yield fine detail.
The engraving results tell the story if your power setting is correct. Not enough power and the engraving result looks uneven and partially etched. Too much power and the glass or crystal will start to flake and the characters start to lose definition. Way too much heat will actually crack or shatter the glass or crystal so best to start low with your settings and work your way up.
Creating Professional Results
Controlling the focused heat energy is the key to achieving professional results and there are several methods to achieve this. The idea is to provide enough heat to allow etching of the top surface while not overheating the region and to cause flaking. There are several simple and practical methods to achieve the same result and I recommend you take to the time to work with each method to find a process that works consistently for you.
A note about the material: glass and crystal vary in types and formulation. You may have to formulate settings and techniques for several types such as lower end molded glass, flat glass sheets and crystal. The highest level of caution should be used with leaded crystal. Remember that we are using heat from the laser and the lead in the crystal will retain the heat and the results can often result in shattering. My recommendation is to not take in customers’ vintage crystal for laser engraving, period. Modern leaded crystal has a lower lead content and it is advised that you only laser engrave leaded crystal that you provide and have tested for engraving performance.
Diffusing the Heat
There two different techniques to diffuse the heat from the laser to create high resolution engraving on glass and crystal. Each technique has its benefits and I recommend you take some time to test each one to find the simplest method for you to use. Your technique should be one that becomes something you can repeat in production so you can knock out engraving jobs with ease. The first technique involves direct engraving and adjusting the settings and the engraving graphic. The second technique is based on adding a material to your engraving substrate to act as a diffuser. Before starting out on any engraving job be sure to clean your glass or crystal with window cleaner and a soft towel to remove any residue or fingerprints.
In our Laser Clinics we like to teach the method of adjusting laser settings to achieve best quality results on glass and crystal. This method is by far the simplest but does take some time to tune the settings of your systems. Start adjusting your engraving speed to 70. This will give you more consistent results compared to using a speed of 100 especially on shorter lines of text.
Lowering the DPI also helps to spread out the laser pulses and effectively reduces the heat in a small area. It would not be uncommon to use a DPI as low as 200 for soft glass. A typical DPI for crystal or a higher quality glass would be 300 or 400.
An additional method to spread out the laser pulses would be to use a 70% black fill color in the text or in a graphic. The laser tries to recreate a shaded pattern using halftone generator in its print driver. The result on the substrate is a pattern of laser pulses. This technique is especially helpful with large text or graphics that have a solid fill. Without using this technique the engraved result may look uneven and have flaking in the large fill areas.
Adjusting the power setting is the last variable and is the most important part. Try one of the above laser or graphic settings with a variety of power settings. Vary your power in units of 10% and first and then fine tune them in units of 5%. The optimum results will have the best detail with no flaking of the top surface.
A completely different method to diffuse the laser energy is to use an add-on material to the substrate. The simplest version of this technique is to use copy paper soaked with window cleaner. The advantage of using window cleaner is that it quickly soaks into the paper and stays wet. Typical copy paper is the 20lb variety and it works well because it is consistent in density. The soaked copy paper is applied to the substrate in the area of the engraving prior to engraving.
The wet paper technique can yield some excellent results using a wide range of laser settings. I would recommend this process for smaller engraving areas as the wet paper dries out fairly quickly. Once the paper dries out it can ignite from the laser so it is best used for one to two lines of text.
Creating Sand Blasting Masks
For many the look of direct laser engraved glass is not ideal. While this is more of a personal preference there is a need at times to etch deeper in the glass or crystal. A deeper etch creates a more elegant look on large items and also is needed if adding color to the engraving is to be done.
The process of creating a mask for sandblasting is very simple and starts with using a laser safe masking material. A laser safe material does not out-gas hazardous fumes during the engraving process such as materials made from PVC.
Two materials that work well for this application are the red polyester masking materials and Green Laser Tape. The red polyester tape is rigid and best for flat items while the Green Laser Tape is flexible and easily applied to compound curves.
Once the laser safe mask is applied to the glass or crystal, laser engrave through it and into the substrate. Since we will be sand blasting the engraving quality is not significant as long as the mask is vaporized completely. After sandblasting, spray or brush on the paint and peel the mask off.
Fused on Color
The most durable method for creating color on glass is to fuse it on. This process is called thermal bonding and uses the heat energy from the laser to fuse a coating on to the glass or crystal. If you have been marking metal with CerMark the process is identical but the material that is sprayed on is different.
The process starts with a clean glass and spraying on a thin coating of the marking solution. Hold the spray can 10-12 inches from the glass and use slow and even passes to create an even coating. The marking solution will dry in about 15 minutes and it will be ready to engrave. Set the laser to 50% speed and 100% power if you are using a 50 watt system and engrave text, logos or even photos.
After engraving the un-engraved CerMark washes off with water to reveal the engraving. If the texture of the laser bonded engraving is rough it can lightly buffed with a Scotch Brite pad to improve the look.
So just how durable is the color that is bonded to the glass or crystal? Extensive testing has shown the fused on color can withstand over 100 dishwashing cycles without any degradation.
Many types, many markets
The many types of glass and crystal available is virtually endless and so are the markets. Understanding which laser process to use with the type of material is critical. Take your time and invest in the education process required to produce outstanding results with your laser. Document your success so you can reproduce pro quality results on a variety of materials. Once the basics are mastered you will be open to new markets and new applications that help to build your business.