I did some digging to see if there was prior art in the GF Community regarding engraving/scoring Plaster of Paris. I didn’t find anything conclusive - but there was mention of it not being toxic or dangerous to the GF but that I should cover up the circut board nearest the heat sink to protect it from any dust from the Plaster of Paris (so I did that). Plaster of Paris mentions 1 Plaster of Paris mentions 2
My current obsession is making old plaster plaques from the '70s into something new for today. I’ve taken a few plaques that I’ve found at thrift shops or bought off of eBay and turned them into new blanks. I did this by using a dremel to grind down the lettering, smooth out the surface with a thin layer of soft Monster Clay, hit that with an embossing tool heat gun (much lower temperature than your standard heat gun) to smooth out the surface, create a mold with a piece of plexiglass, cardboard & make a mold with 2 part silicone. Pour the plaster of paris, repeat until you have a stack of blanks to work with.
My GF settings are score at 260/fp/1 pass. I’m using the font UNLEASH because it looks hand drawn, the caps are wide and it gives me a good surface to paint to make the saying stand out.
What I’ve done is use the text tool in Inkscape to change the font from a fill to a stroke, change the text to a path, duplicate the path, change the duplicated path to an Outset path, repeat the process around 6 times or so, making each additional duplicated path another (larger) Outset path. This results in the central text being ringed in several other score paths which I then can break away from the surrounding plaster with a toothpick so that there is a gap between the letters and the surrounding plaque. We know that scoring is MUCH quicker than engraving and each of these plaques were scored in less than 6 minutes each.
The clean up (removing the scored bits and prepping for painting) took considerably longer but I’m really happy with the results. I love the mashup of something old as something new. I have so many ideas for what to put on the blanks, that I need to pour more plaster blanks!
Surprisingly enough, there is very little Plaster of Paris dust inside the GF after making 3 or 4 plaques. I thought there would be a lot more mess than there is, but I guess it’s all getting blown out the window vent. In any case, it’s not the messy disaster that I thought it might be.
I laid them down in front of a fan for several days, turning them over several times each day. Once they were bright white, lightweight and no longer cool to the touch, I proclaimed them “ready”.
Thank you for sharing your technique. I bought some plaster of paris a couple years ago - now I can’t remember why! Ooh, I think it was to make my own chalk paint. Now you’ve given me something new to think of doing with it!
Probably? If I had all the time in the world, I’d make these in clay and have a mold of letters at the ready & assemble them as slab construction/pressed plaster mold work - BUT I love the flexibility of being able to do a one off with the laser. The sky is the limit!
Sorry to be late to the party but there is a reason why you do not get plaster dust everywhere …
Plaster of Paris is de-hydrated gypsum. Gypsum is a naturally forming non-metallic mineral, found as a rock or sand composed of 70.1% calcium sulphate and 20.9% water by weight. Its chemical formula is CaSO4 · 2H 2O .
What you are doing is creating CaO (calcium oxide) and H2SO4 (Sulfuric Acid). The reason vinyl is a no-no is that it results in Hydrochloric Acid, and I think Sulfuric acid would have about the same effect.
I’m not sure that’s the case. If it were then I think we’d see a lot of acid-eaten lasers out there.
The “Plaster of Paris method” is a common technique for marking stainless steel for people who don’t want (or can’t) but Cermark or other laser marking spray. You’ll find it all over the generic laser forums like Reddit threads, some woodworking/making forums and even laser manufacturers like CK.
I’ve been out of the chemistry world for too long to remember how the affect of a laser in calcium sulfate would work. It might not actually split the molecules as you think.
The lack of reported problems combined with the apparently successful regular use suggests to me there’s more than meets the eye here. The generic SDS breakdown of constituent parts when burned may not apply in this case (my gut suggests it may be like aluminum where the laser is ablating the plaster and not burning it).
It could be the chemical bond of CaSO4 is far stronger and does not deconstruct to leave itself open to forming H2SO4 and CaO. In fact I’d bet that CaO is not a strong enough bond to favor breaking the CaSO4 bonds.
My daughter runs a chem lab for UC Boulder and is visiting. I’ll ask her about this and report back.
Now you’ve given me something new to think of doing with it!