Finally got around to testing some slate with the 10W. Done at 2000mm/m, 100% power, 0.1 interval.
Slate lasers REALLY well.
EDIT: They’re sitting on my diningroom table. It’s cherry and rock maple @ 4.5cm thick. 
Slate lasers REALLY well.
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Was going to try some myself soon. So the lasered part comes out ‘whiter’ than the base color? Just want to plan my designs right (invert or not).
Assume I can ‘grayscale’ with rastering, with the unlasered color being darkest?
Yes, the laser part becomes lighter. You’ll have to invert your images for them to appear correctly.
I did these in grayscale, stucki.
Thank you for the reply and the dry/wet pics!
I’ve seen some sites recommend sealing slate cheese boards with mineral oil to help reduce moisture and biopentration from food (or I guess just pre-displace it with the oil), and another actually recommending using walnut oil which is food safe but also oxidizes and more or less ‘solidifies’ in place as a sealer. (A partially known trick for ‘repairing’ scratches in wood furniture is to just rub it with a raw walnut, the walnut meat/oil ‘packs’ into the scratch and hides it well, darkens it a fair bit, and walnut never really goes rancid.)
Not sure if on a coaster either would be a good idea, might just cause cold drink condensation to skate right off…but wondering if it would help preserve the laser engraving longer to wear damage.
Anyway, hope to do at least one of my own tests this weekend, still working on the designs. I think grayscale art is what I want for some, for others I might ‘halftone’ but horizontal (going for a kind of old school monitor scan line look on that design), but for others more pure vector lines so I have to be careful about my layers and buildup in the SVG source. I’m not the best illustrator by any means, just semi randomly fumble thru Inkscape until it eventually looks the way I want but then half the time have used big white blocks to mask things in layers and need to screencap the result and re-import the whole thing as a bitmap trace to vector --pathetic! 
Nothing is pathetic if it gets the end result you want.
These look nice! I need to try some myself.
I’ll keep an eye out if you make sure to post them.
With mineral oil it seems to work fine still for condensation. (In So Cal, so not crazy humidity)
I wouldn’t worry about wear damage. It’s pretty darn permanent. Although if you make a mistake you can use wet sandpaper and sand off the marking and redo it. But it takes a lot of elbow grease to get it off.
As far as grayscale goes, you’ll want to use dithering. Unlike wood where you can get different shades/levels of burn, with slate it’s pretty binary - one level of white/gray.
-S
Finally did my first! 1800mm/sec, 0.1mm spacing, B&W mode from an SVG vector import, 100%
Raw surface after lasering:
I’m surprised that the lasered part actually feels a tad ‘raised’ and in my case is a tiny bit warm in color. Perhaps I bought cheap arse tannish slate dyed to look more dark gray and the lasering is counteracting it. (Although looking back on the detailed pics posted, I see that same warm tone in theirs so I guess mine’s on par.)
Next step trying that soapstone sealer (mix of carnuba wax and walnut oil), then after a few day cure test if I’ve totally violated using it as a coaster allowing some moisture to absorb…
It’s just natural variance in a natural material. It varies from slate to slate. I haven’t figured out a way to tell how it’s going to turn out beforehand.
-S
I had a raising issue as well… almost like it crystalized the image and raised it above the surface of the coaster about 0.2mm. What causes this? I’m sort of wondering if I’m burning too slow (500mm/m) or if I too bought shite slate-ish coasters.
In retrospect I think I actually like it, and that’s just how the slate ‘converts’ I guess.
I have one I burned raster-dot style, that looked fine when ‘raw’ but as soon as I added a little of the Soapstone sealer I liked on the others, it was way too “dim” (low contrast). So now to me that crystalization/raising feeling is the indication I burned enough.
Image has the 3 at the right all with the sealer, and the top left without still. (Reflection angle is unfortunate…the LV-426 coaster has scan-line-corrupted text below the ship that says “send more colonists” 
They look damn good man. Where you got those from? I am actually interested in making collection of different things and I would also like to have these drink coasters added to my list.
I just get them from Amazon. You have to be a little careful to get the best deal, but last time I bought some square ones, 12 for $15.
At least a dozen vendors on Amazon. Buyer beware, of course…it’s all going to crap it seems.