A recent client sent me a few small precious gemstones to see how easily they could be engraved. I did some tests on them, with varying results, and sent them back her way. We went with a really simple five point star to test the engraving quality—with the smallest one just .07″ in diameter!
Out of this initial batch, the topaz and quartz both engraved beautifully, but the opal’s engraving was basically invisible. This is probably due to a combination of factors. Opal is completely opaque, so no light can come through the material to highlight engraving. It’s a consistent color throughout, and it doesn’t burn, which means the untouched surface is only different from the engraved surface in texture. It’s very hard to capture in pictures.
My client received her gemstones back, and made some observations: in one piece, the horizontal lines that make up the engraving (because of how raster engraving works) were visible even at the laser’s highest engraving density setting. She also felt that the engraving wasn’t very deep and was wondering if a deeper engraving would affect the overall quality of the engraving.
Conveniently, I found out that Jennifer had done some tests on gemstone beads before, so we had some quartz of our own, as well as some garnet, to do tests. I became determined to solve these problems and answer these questions without requiring a new shipment of gemstones.
I was pretty shocked to see that the individual lines of the engraving were visible; this is something that happens on lower density settings (like 4, which is used to reduce engraving time but can leave ultra-fine gaps between the lines in certain materials). At the max density, this normally isn’t visible at all. I decided to try to engrave my pieces slightly out of focus, increasing the laser point’s diameter so that each pass overlaps somewhat.
As it turns out, though, none of my testing worked quite the way I’d hoped it would. Maybe the gemstone beads’ facets were impeding the engraving, or both of my solutions weren’t solutions at all, but all I got out of six different attempts were excessive chipping and almost unrecognizable engravings.
They’re supposed to be hearts! While I engraved the first batch with stars, I figured hearts would be a good shape for the quartz and garnet beads. I don’t think the shape mattered much in the end.
I engraved three pieces of quartz. From left to right, I gave them one engraving pass, then two, then three, at the same settings I used for the client’s quartz seen above. This time the chipping was so severe that you almost can’t even see the difference between the three tests, but upon close examination the heart that was engraved three times was actually a deeper engraving—completely moot with how poorly it turned out.
For the garnet, I was testing whether engraving out of focus would result in a smoother engraving, and it certainly doesn’t seem to be the case. Perhaps the offsets (focused, 0.5″ out, and 1″ out) were too severe a difference to see any value, but even the focused heart on the left was nowhere near as clean an engraving as on the client’s gemstones.
So I think the moral of these disappointing results is to always perform subsequent tests on the same exact material. I wasn’t able to give my client a good answer to her questions with these tests. Still, I’m fairly convinced now that chipping will prevent multiple passes from getting a deeper engraving without reducing the engraving quality, but the jury’s still out on whether adjusting the focus can have a positive effect. We’ll find out eventually!