Laser engraver
Lasers are easiest to use on a flat surface. That is, they require a specific focal length or distance between the lens and the surface being marked. When the item to be marked is curved, a laser is very limited. There are a couple of tricks that allow some flexibility here but even then, the distance around the curvature of an item is severely limited.
When engraving steins, wine glasses, vases, wine bottles and the like, using a rotary attachment can make the task much easier but still variations in curvature and complex angles can be a concern. Also, handles on steins can interfere since they may protrude enough to actually bang against the lens assembly as the cup spins around in the rotary attachment.
Because lasers use a lens, they have something called “depth of field.” This is the distance between the nearest point of sharp focus and the farthest point. Outside this narrow range the laser spot goes out of focus and consequently the image becomes blurry. Anything within the lens depth of field will laser engrave on glass and appear to be in focus. This gives us the ability to work with products that have a slight curvature to them such as plates, wine glasses, etc. Although not ideal, we can focus the lenses at the two extremes of this focal length and allow the image to wrap around the object with little or no visible distortion. To do this, you will need to determine the distance your lens will allow you to drop out before distortion becomes visible.
Generally, we “engrave” glass hot and fast. On a 25 watt laser, we laser glass at 100% power and 100% speed. I want the laser to strike the glass, do its thing and move on. Not everyone agrees with this technique and to them I say, “If something else works better for you, do it. This is what works for me.” I also recommend turning down the PPI of the laser to about 300. This better spaces the heat out over the glass and will reduce the tendency for the glass to create shards (tiny specks of glass caused by severe fractures). I want my engravings to be shard free, although that’s easier said than done since every piece of glass can behave differently.
Many engravers like to place a layer of wet newspaper or paper towel over the glass to keep the heat from radiating as much. This too is intended to reduce the number of shards. I have mixed feelings about this technique. Sometimes it works very well while other times, it doesn’t. I find it very helpful when marking wine bottles or using higher power lasers. To try this technique, wrap or cover the item with a piece of newspaper and then spray liberally with water from a spray bottle (add a drop or two of dishwashing liquid to make the water absorb into the paper faster and more evenly). If the paper begins to dry out while engraving, just stop the laser and spray again but do not physically touch the item being marked.
The objective of lasered glass is to leave a frosty mark that is easy to see and smooth to the touch. Running too hot or at too many pulses per inch (ppi) will create excessive heat and depth to the mark. Although this may sound advantageous, it really isn’t because of the shards and uneven engraving that will result.
After engraving, the glass may need to be cleaned up a bit. If shards are present, use a nail brush to remove them. Cleaning the glass will usually be necessary. I use rubbing alcohol in a spray bottle and a Bounty paper towel. The alcohol cleans oils off and dries quickly.
Sometimes it’s nice to add some color to engraving. Other times, the nature of the glass may allow it to be marked but the mark is difficult to see or the image is so highly detailed, the detail is lost due to reflections off the shiny glass surface. One way to solve this problem is to add Rub-n-Buff. Rub-n-Buff is available in 18 colors from most craft suppliers. It comes in a small tube and is applied best with the tip of a finger. Very little is needed since this stuff goes a long way. Rub-n-Buff is not intended for glass so the instructions on the tube are not appropriate. The instructions say “allow to dry.” Do not do that. Apply the Rub-n-Buff and remove excess prior to drying. Otherwise, you may never get this stuff off. Once dry, it is relatively permanent.
One of the biggest problems with lasering glass is that glass often varies in size and shape. Even two wine glasses that look just alike may actually be quite different in size and shape. This affords a considerable challenge to engraving them. For me, the magic button for engraving glass lies in two things: One is something I call “Sample Engravings” and the other is the ability to create simple jigs or fixtures to hold the glass in place while being engraved.
What I mean by “Sample Engraving” is simple. Place a sheet of tag board, paper or cardboard on the stage of your laser. Adjust the focus and actually engrave the image on the cardboard. Now, all that you have to do to be sure the glass is positioned “just right” is to position the glass over the engraving so the engraving on the cardboard is positioned exactly where you want it. Then, re-focus and engrave the job again. No offense but it’s pretty hard to mess up a piece of glass using this method.
The other key is the building of “quickie jigs” or fixtures to hold things like wine glasses or other odd-shaped items so they don’t accidentally move while being engraved. I usually do an “idiot engraving,” then build my jig around it. This not only holds the piece in place, but it allows me to do multiple pieces quickly and easily. Items that vary slightly in size are easily accommodated because of the sample engraving on the cardboard underneath. The fact that items don’t have to be clamped in place is where a laser really pays off in the glass market. Marble trophy bases make great temporary jigs. For round products, consider a roll of tape. I keep several rolls of masking tape around. One has 1/2" wide tape, another 3/4", another 1" and so on. By adding these 3" hubs of tape together, I can create a wide variety of fixtures to hold oddly shaped items.