Comment by CliffStoll

In short - engraving borosilicate is difficult, because it does not expand very much when heated. So when hit by an infrared laser beam, the glass doesn't locally expand and spall off a tiny speck of glass .... instead, the glass locally melts. When the beam moves on to the next pixel, the first site either solidifies or sometimes dribbles away. Laser engraving of borosilicate just doesn't work well. And, because of the compound curves of the Klein bottle, you need a big depth of field as well as a rotary bottle holder. All laser engravers that I've played with have a very short (10mm or so) depth of field. Diamond engraving doesn't work well because of the curves. Sandblasting with a rubber mask works, but making the mask is a pain. So, after lots of attempts, I've given up on engraving these guys. Also: mistakes are expensive -- this is hand-blown glass.