While white text and other design elements are perfectly acceptable, I can say without exception that any grayscale or photographic image must be inverted to make a positive image on glass and clear cast acrylic. Unless it will be color-filled, laser engraved marks on glass and clear acrylic are always white. Even though the material is clear, glass and clear acrylic can be considered to be a dark material. Put an engraved glass in front of a white background and the engraving will disappear. It has to be seen against a dark background.
Also remember that if engraving on the reverse side of glass or clear acrylic, the entire drawing needs to be mirrored. That way it will look normal when viewed from the front through the material. Glass seems to be the medium where most of the negative image mistakes are made. Sadly, I’ve seen negative images on projects as large as church door windows.
—COOLaserCraft
