There are two ways to provide artwork for raster engraving, the fill in engraving shown on the board engraved for the Royal Botanic Garden Edinburgh above.
Pixel based files
Pixel based files include png, jpg and bmp files. They must be provided in black and white at a print quality resolution of 300dpi or greater to ensure good quality engraving. Any pixellation in the image is seen in engravings!
Sometimes, customers provide artwork from the internet. While these look good on a computer screen, they aren’t good enough for engraving (or printing) as they’re only 72 or 96dpi.
And if pixel based images are rescaled, they can lose quality and become pixellated the more they’re processed through resizing. All these potential problems can be avoided by using vector files.
Vector files include ai, pdf, dxf, eps and svg files. They are made up of vector lines, not pixels as png, jpg and bmps are. Artwork for the engraved board at the top was created by pdfs and is shown below.
A huge advantage of vector files is that they can be rescaled to the size a customer wants without loss of image quality. Files are rarely provided at the scale required for a job, which means that resizing a logo or other artwork is inevitable.
Vector files also need to be black and white with no greyscale.
Why black and white?
Lasers can’t engrave in colour. The colour of engravings depends on the colour that the material becomes when it’s burned by the laser at the speed and power selected. In the case of wood, you can get deeper shades of brown and greater depths of engrave with increasing power or reduced engraving speed.
As the laser either engraves or doesn’t engrave, artwork needs to accommodate this. Generally, I recommend that the parts of a design to be engraved are black and non engraved areas white. Shades of grey can be achieved with different densities of black pixels like old fashioned news print, and the black pixels will be engraved to give a grey effect.
Why doesn’t greyscale work?
When the laser sees a shade of grey, it decides whether it’s dark enough to be black and engraves it as black, or decides it’s light enough to be white and doesn’t engrave it.
Have you still got unanswered questions? Email me at firstname.lastname@example.org.