I'm one to advise 'less is more' quite often when lasering--
I just ran off a big 30oz 'SIC' yucky green flask, it turned out nice (as usual) and thought I'd share some pics and settings...
First, unless the coating is thin or isn't actually powdercoat, I ALWAYS run powdercoated flasks in 2 passes, I've found, with my machines, trying to get them done in one pass just doesn't work. As to 'less is more', this is a pic where I stopped halfway thru the 2nd pass. Note that the first pass almost reached bare metal, but didn't...
pc1.jpg
Closeup, shows the 2nd pass cleaned it off perfectly. And there's no sticky left behind. However, that's partly a function of this color, some colors aren't so friendly
And note the engraved edge, shows the thickness of the coating, this is pretty typical, not thin at all, but not too thick either...
pc2.jpg
This is a 'size reference' pic, this is a big cup, and that's quite a bit of real estate engraved...
pc3.jpg
My settings, although hard to read, so I'll translate
pcstats.jpg
Speed: 38% (of 80ips) - Power: 100% (30 watts)
DPI res: 380 (which is this machine's "400")
and most important, the clock: 1:58, which is per pass, so both passes took less than 4 minutes total for a fair amount of engraving. Not bad!
I've found that higher DPI is counterproductive, as is slowing the machine down, to attempt one pass runs, what I get is more initial coating removed, but with a lot of goo left behind, more than can be wiped off with DA or acetone. And that goo is harder to remove by laser than the base coating. My theory is, my light 'just enough' passes are causing the coating to better vaporize, for whatever reason. More power seems to overheat it...? Depending on the cups and coatings, I'll vary my speeds between 38 and 30%, and DPI between 380 and 300. I never go slower than 30%, or go into 500 or 600 DPI territory. And I get very good results with only 30 watts, definitely fits the "less" part