What stone are these made of, and how do I clean them?
February 17, 2018 5:54 PM   Subscribe

I bought a chess set cheap on eBay. It was advertised as agate and jade, and mouldy. It's certainly mouldy, but I'm pretty certain it's not agate and probably not jade. Can anyone take an informed guess at what type of stone these are made of, and how to clean mould off them?

The white pieces have a warm quality to the colour rather than a cold one, if that makes any sense. The greenish ones are translucent with dark flecks in them. They were in what I think is the original box, which was not great quality, so I doubt they're anything expensive,. A hot needle doesn't mark them, so they're almost certainly not resin. No idea of country of manufacture.

I know nothing about identifying stone apart from the results of a few web searches.

According to the seller the set had been stored in damp conditions, and there is a residue of light-coloured mould in the fine details and grooves of most of the pieces. Soap, water and a soft scrubbing brush hasn't been able to get rid of it. I don't want to risk anything more caustic without being sure it's not going to damage the pieces.

Any advice would be very gratefully received.
posted by Hogshead to Science & Nature (11 answers total)
My guess is the green is soapstone and the white is alabaster. Each requires a slightly different cleaning method.
posted by Thella at 6:19 PM on February 17, 2018

My husband thinks they’re both soapstone. I think the white looks like quartz. (Do they make the same sound if you tap them gently?)

I found this resource but can’t vouch for it. Assuming the pieces truly are natural stone, it suggests ammonia, bleach, or hydrogen peroxide diluted with water. (Obviously this is one-or-the-other; certainly don’t mix ammonia and bleach!)

Heat might also be enough to disinfect them, but I’m just spitballing here.

Naturally you’ll test one helpless pawn first, whatever you decide...right?
posted by armeowda at 8:06 PM on February 17, 2018

They look like soapstone to me.
posted by limeonaire at 8:28 PM on February 17, 2018

I was gonna say soapstone.
posted by matildaben at 9:34 PM on February 17, 2018

I wanted to recommend an ultrasonic cleaner, something like this, that people use to clean jewelry. I’ve never used one, but it seems designed to get crud out of tiny crevices.
posted by cabingirl at 3:27 AM on February 18, 2018

If you decide really hot water and detergent would be ok, consider a high-powered dishwasher, the kind that takes the paint off stuff.
posted by AnOrigamiLife at 5:43 AM on February 18, 2018

Brush with cheap stannic fluoride toothpaste and wipe with cloth , if you can scratch the bottom with a steel point it is neither jade or agate . Jade likes oil to shine. If the stone is a carbonate like marble, using detergent could cloud the polish .
posted by hortense at 8:32 AM on February 18, 2018

White marble, green onyx I think is the answer. The mould may be a sellers attempt at antique patina.
posted by hortense at 11:53 AM on February 18, 2018

Many thanks for all of these suggestions. Following up a few questions:

* There's no sign of banding so I don't think it's onyx (though I've found a nigh-identical set on eBay, same board and piece-designs, but those pieces do have onyx-like banding on them so it could be. That board was clearly marked 'Made in China' so it's likely to be a stone that's easily acquired in east Asia).
* Both types of stone can be scratched quite easily. I'm pretty sure it's nothing valuable, but it looks nice and I want the kids to have a good set to play with.
* I'll give toothpaste a try before anything else, on one of the minor pieces that's already had a few knocks.
posted by Hogshead at 12:40 PM on February 18, 2018

One more vote for soapstone. Lots of Mexican carvings look like this.
posted by fiercecupcake at 3:22 PM on February 18, 2018

I'm a geologist, and like most geologists, the worst question you get is identifying a small polished stone -- completely out of context, no weathered surface, no natural fracture or face. It's obviously harder with a photo over the internet.

But if I had them in my hands:
Both soapstone (talc) and alabaster (gypsum) you can scratch with your fingernail, but soapstone will have a 'greasy' feel. Marble won't be scratchable with your fingernail, but a metal fork or knife will scratch it. Neither onyx or jade will be scratchable with metal.

Colour is rarely diagnostic.
posted by bumpkin at 12:35 AM on February 19, 2018 [1 favorite]

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