Holey Marble!
August 20, 2010 2:34 AM   Subscribe

How do you chemically carve a hole in a piece of marble or granite?

What chemical substance can be used to make deep holes through a piece of marble or granite, for artistic (sculptural) purposes?

How can I acquire it (is it readily available on the market for the public) and use it safely?
posted by howiamdifferent to Media & Arts (18 answers total) 1 user marked this as a favorite
Marble is a mixture of calcium and magnesium carbonate minerals, and any reasonably strong acid ought to be able to make holes in it, albeit slowly. I don't know how you'd manage to control the size and shape of the hole produced.

Granite is composed of silicate minerals, and you'd need hydrofluoric acid which is very nasty stuff indeed. It's been a few years since I did rock digestions, but my memory is that even very small amounts had to be powdered quite finely and left for a long time in warm and reasonably concentrated HF to get them to dissolve. I think you're out of luck with making holes in granite by chemical means.
posted by nja at 2:54 AM on August 20, 2010 [1 favorite]

Safely? No idea.

Thermite is probably strong enough to melt a hole straight through pretty quickly. Not very easy to control though and obviously, it's a huge fire, so quite hazardous.

A very strong sulphuric acid or hydrofluoric acid would work too I think. A lot slower but maybe that would make it easier for you to sculpt with it somehow?
posted by public at 3:00 AM on August 20, 2010

HCL...concentrated for the granite.
posted by hal_c_on at 3:02 AM on August 20, 2010

Marble is definitely the easier choice (any acid will work, though getting a concentrated enough supply may be tricky), but whatever you do, DO NOT USE HYDROFLUORIC ACID (HF)! That stuff is seriously bad news.

As for safety with conc H2SO4 or HCl, they're not nearly as bad--and you shouldn't be overly paranoid--but they are capable of seriously messing you up if you don't know what you're doing. The best idea would be to have somebody well-trained physically present.
posted by Dr.Enormous at 3:08 AM on August 20, 2010

Can I ask why you wouldn't want to drill the marble? It's a relatively soft material and quite easy to drill, as long as you take it slow and irrigate the hole.

Thermite will melt granite, but there's no practical way you're going to contain the reaction in such a way as to drill a deep hole. The most likely scenario is that you'll end up with a big puddle of thermite and melted rock, then a bang as your block of granite violently cracks apart.

Don't mess with hydrofluoric acid (or for that matter any concentrated acid) unless you have all the safety equipment and training needed to do so.
posted by le morte de bea arthur at 3:18 AM on August 20, 2010

I'm with bea, the chemical is called steel and the pourer is a drill. Something tells me this might have more to do with the chemical process than the rocks, though.
posted by rhizome at 3:23 AM on August 20, 2010 [1 favorite]

At the concentrations you'd need to use, hydrofluoric acid is indeed VERY nasty stuff.
posted by Ahab at 4:22 AM on August 20, 2010 [1 favorite]

Further to Ahab's link: when I used to use it in university labs about 25 years ago I had to wear a full-face visor and thick rubber gloves and apron, and this was for handling quantities of a few millilitres in a fume cupboard, digesting rock samples of the order of a milligram of weight. I believe even postgraduates aren't commonly allowed to use it these days. It's really not something for amateurs to even think about using (nor would be anything else which might be capable of chemically burning holes in granite, come to that).
posted by nja at 4:50 AM on August 20, 2010

Back in with an apology - sorry that my comment just now wasn't an answer. I was more than a bit horrified at the thought of you sloshing on the HF and dying as a result.

As I understand this, hydrofluoric is almost unique in that it dissolves the silicon dioxide in rocks. So for a fast "carving a hole" effect, strong HF might be the only option. But it remains one you should not use because it is just too dangerous.

Depending on the effect you want, it might be possible to use a very very weak solution of hydrofluoric to repeatedly etch a particular area and thus make a hole. In a lot of places, you can buy weak HF as "glass etching cream." I'd still be dubious about the safety of this.

However, granite isn't just silicates. It's felsic, meaning that the silicates are bound up with metals. Those metals can be dissolved by other acids. If you were to use another strong acid (which is also very dangerous, but less so) and (for instance) neutralize the acid before washing out the resulting holes with a pressure hose or something, you might get an interesting "holey" effect. There's probably waste disposal and environmental contamination associated with doing this, but you could conceivably sort that out.

But I think your best option is to stick with the marble. Marble literally dissolves in water, and you can badly ruin a bench or tabletop with lemon juice. So it'd be not only safer, but a whole lot easier, to work with.
posted by Ahab at 5:26 AM on August 20, 2010

It's not just steel. It's steel and water that cuts it.
posted by watercarrier at 5:46 AM on August 20, 2010

Just to re-iterate on the dangers of HF: Besides being one of the nastiest acids available, it is also a contact poison. It will seep through the skin without creating much sensation and then fuck up your blood chemistry (I want to say it precipitates out with calcium, but don't quote me), to the point where you need to be rushed to the hospital before you drop dead.

So I would advise against using it.
posted by Dr Dracator at 8:50 AM on August 20, 2010

Chlorine Triflouride should cut it nicely.
posted by Confess, Fletch at 9:43 AM on August 20, 2010

I assume that you're averse to using simple power tools (e.g. a drill) because you're after a fluid/organic/semi-unpredictable effect for artistic reasons. The nasty chemicals plan seems...nasty. Maybe look into abrasion? (pressurized water or air with suspended abrasive particles)
posted by madmethods at 9:53 AM on August 20, 2010

Carbon crystals and mechanical action.
posted by hortense at 10:36 AM on August 20, 2010

I'd rough it out with a diamond burr and then do some trial and error with chemicals to see what aesthetic effect I can get. Flowing HCl would be a little dangerous but would work an order of magnitude faster then just pooling it.
posted by Dmenet at 11:01 AM on August 20, 2010

Thank you all for the informative responses.

The reason I wanted to go with chemical methods is that I wanted to have an organic, "cavey" effect, as madmethods pointed out. I plan to reach that effect through leaving a chemical substance to drip over different parts of the marble piece for a while.

Since, judging from most responses, using an acid such as HF is pretty much suicide, what alternative do I have? Can I get the same effect through pressurized water?
posted by howiamdifferent at 3:43 PM on August 20, 2010

Good call on avoiding the hydrofluoric acid.

This definitely sounds like a good concept. It's making me think of art nouveau cameo glass and modern Scandinavian sandblasted or etched and cased glass. If you could find a way to do similar things with stone, that'd be awesome!

First step towards an alternative would be to use a stone that isn't mainly silicon dioxide. The repeated mentions of hydrofluoric acid above are connected to the idea that you'd need to dissolve the silicates in stones such as granite.

If you're using marble (mostly calcium carbonate), you could use much weaker acids. Over time, even acids as weak as lemon juice and vinegar will completely dissolve marble. If you wanted something quicker, I think you'd use a stronger acid, but you shouldn't need to scale up to anything much stronger than you'd find in ordinary household cleaners. Have a look at Wikipedia for the chemistry side of this. Or google "how to dissolve marble."

I'm guessing, but only guessing, that if you weakened the structure of your marble with a weak acid, then hit it with pressurized water, that would produce a different effect to simply dissolving it. Possibly a better and/or more controllable effect.

Marble also has the advantage of being soft. So if you wanted to pursue sandblasting, marble would again be much faster and easier than something silicon based like granite. There's a few safety concerns with sandblasting (don't get in front of the gun, wear an appropriate mask, goggles and other protective clothing, etc). But they're nothing compared to working with crazy acids that seep into your bloodstream in seconds.

Why not start by picking up some small pieces of broken marble from an interior design place (or a gravestone factory), and dribble some weak acids and household cleaners on them? See what works.

And good luck!
posted by Ahab at 5:50 PM on August 20, 2010

Pool acid will dissolve marble shockingly fast, spatter some asphalt or wax resist mask on the stone to leave an undercut etched edge.
posted by hortense at 8:30 PM on August 20, 2010

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