That’s what I had always assumed…Interestingly, the folks at Epilog agree with what the folks at Glowforge have done…
Article here in case anyone is interested enough to read about it:
“5 Common Mistakes in Laser Engraving and How to Avoid Them”.
I decided to run a little test anyway…for science.
So I set up a little circle engrave, going in one direction, on messy thick draftboard. Ran the engrave, then turned the circle around 180° and engraved over it again, so the laser was burning up all the crap and resin that had been deposited over the open engrave from the first pass.
Want to know what happened?
About what you’d expect…the resins were fused into a glass-like substance in certain spots, giving a really lousy looking uneven engrave.
It’s really hard to capture with a camera, (sorry, my close-up was a little too close I guess), but the dark patches and spots that you can see in the image are glassy, smooth and fused…they are not the same texture as the rest of the engrave.
And worse, if you try to scrape the glassy bits off with a fingernail, it removes the effect of the engrave. They are really fused on there.
My conclusion based on this run is that the folks at Glowforge know exactly what they’re doing by running the engraves from bottom to top, depositing the soot and resins harmlessly on top of the already engraved areas. At least the detritus can be brushed away doing it this way.