In my area, center of Arizona, I get all kinds of rocks, some volcanic and some sedimentary and probably everything in between. Some of these work well, some just end up as glass.
This is a volcanic rock done with the 60W fiber…
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Is that what you could call Glass in the right column.
If you could get some depth with a suitable rock type and of a different color, then fill the engrave nearly up to the top with dust from the rock in the pic..Then Laser liquify it, That might be a nice thing.
Sounds like too much work!
Angle grinder with a big box to catch the…Yeah thats too much work!
With some types of rock, one set of parameters can engrave into the rock, while a different set of parameters can vitrify the surface (or make bubbly obsidian-looking glass of you go even further).
I actually use that as a design choice in some of my rocks. A micro-vitrified surface finish at the bottom of the engraved areas can really make it pop, and it also drastically changes how the look changes when dampened.
With other rocks, I haven’t found any good engraving settings for making the deep features, as the rock turns to bubbly glass far too easily. Anything that gets much of any contrast tends to result in vitrified patches just flaking off, leaving the material below unaffected.
Across the range of machines you have tried this technique with are there any more suitable due to Freq, focal length and distance from object.
I ask because the shape of my 20w on snapmaker ray is quite box’y and has a skirt around the bottom to accommodate safety glass and I imagine the hot particles may be less easy to clean off.
What you call hot particles are more like volcanic ash. Extremely fine, gritty, and full of static charge. I found it did not take very many rocks to clog up the iCube paper filter. For engraving rocks, I recommend a good vacuum system with the intake close to the work. I am not even sure a vortex dust separator will catch the particles before the filter.
So it would be advisable to keep the engrave surface level to minimise the risk of damage, or have the head well above the job.
If the particles are full of charge, could that be used to draw them away.
Yes, level and flat are a benefit. And, yeah, don’t crash the nozzle into the rock.
Likely, if you can determine if it is a positive or negative. I do not know for a fact they were charged. It only seemed that way when I was cleaning the iCube. Maybe they were neutral and the iCube was charged, I really don’t know.
It seems that the surrounding environment has the greater influence.
While ferous containing can have a charge and silica, and the air pressurised by the pump can also be either positive or Neg.
Im wondering is the atmosphere in a Faraday cage + or -.
Would a negative ion air assist both neutralise the particles charge and move them in a desired direction.
would an earthed (via gantry and frame) copper plate with a beam and air assist accommodating hole be beneficial…I suppose it would.
I’m far from being a specialist with these. As you can see from the photo, it produced virtually no dust that was found… just heated the rock until it melted. Since it’s a fiber, I do have a number of ways of heating it, but haven’t really tried to engrave with volcanic rocks. From my memory, it was a lot more difficult than I had imagined.
I think about every kind of rock is different and machines differently.
Seem to be, but I don’t think they have any kind of known polarity. First field evidence of the electrical multipolar nature of volcanic aggregates and A review of volcanic electrification of the atmosphere and volcanic lightning have opinions based on relatively new research. Most of this deals with volcanic dust.. There are some neat photos of one way they get charged. 
I’ve got a few samples of rock around, just need to get to them. Thanks for the ideas…
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The review of electrification of atmos is very interesting. I read up to but not including the section on water vapour in the plume.
It appears to be the machining/cracking that predominantly produces the charge.
Some nice terminology and descriptions on particle type, polarity, tendencies, etc etc.
The article you chose paints a sensible view of the considerations, and in terms of lasering rock it seems that to protect the equipment due to its type/design, location or job material, a method of particle deflection or field interference would be most useful.
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