So I tried a quickie engrave of a file I have done before using regular heavy cardstock (a lace photo). It looks like it takes quite a bit more power to get through this stuff vs regular paper. My cardstock conditions for this were speed 635, power 30, LPI 225. The top portion of the engrave below was done at 635/50/225 and as you can see it didn’t get all the way through. The bottom portion was done at 635/65/225 which went maybe a little too deep since I lost a bit of it peeling it off the Seklema mat. Looks very nice though.
One thing to note: the process left a ton of very tiny white particles (I assume calcium carbonate) all over the interior of my Glowforge, which I’m not too fond of. So I’m not sure I’ll try it again. On the other hand there was almost zero burn marking/soot. So there’s that.