Dye on.. rocks?
April 12, 2006 10:44 PM   Subscribe

How are semiprecious stones dyed?

Not heat-treating, dye. Like this. In the case of that rock, loads of pink color washed off after my friend put it under running water. But not all - I'm guessing the dye in the front of it was sealed in by the.. polish?

How do they get it in there? What kind of pigment is it? Is there any way to get it out of a rock, once it's in?
posted by cmyk to Grab Bag (6 answers total)
Your question is a bit unclear to me: did some colouring wash off or not?

In any case: semiprecious stones are not dyed after their creation. Their colouring is the result of the combination of their atoms. In other words; they are the dye.

In the case of fake semiprecious stones; I don't think that is a generally answerable question.
posted by jouke at 10:51 PM on April 12, 2006

I don't know enough about rocks and gemstones to know how to ask, if that makes sense.

On the rock in the linked photo, yes, loads of the pink color washed off.
posted by cmyk at 10:56 PM on April 12, 2006

There are many kinds of dyes that react to different stones and the differently porous minerals within a stone like a geode. This one looks like it simply wasn't done very well, if the dye is running off it. More info here and here.

Yes, they dye it, then polish it with something like cerium oxide, then sometimes seal it with a simple varnish-like material, or a clear acrylic enamel.
posted by frogan at 11:00 PM on April 12, 2006

within a stone like a geode

Duh. You have agate, not a geode.
posted by frogan at 11:01 PM on April 12, 2006

That looks like a geode, which I'm not sure really classifies as a semiprecious stone. It's crystal, usually with some minerals in it.

It seems that they are dyed to make them more garishly colored (especially if the crystal is boring old clear, I bet), to make them more attractive for sale. That particular dye job could have been a really poor one, I don't know.

On preview, frogan even beat me to one of the links. Drat. I still think it looks like a geode.
posted by dammitjim at 11:08 PM on April 12, 2006

Some more explanation finally found here:
I see all kinds of colored geodes, etc.... in the stores that have obviously been dyed. How do they do that?

Most of the Geodes that you find on the market that have been "stained" are of the Brazilian variety. These have gone through a "cooking" in a Sulphuric Acid Bath, under pressure, for quite a while. This process opens the pores of the outer edges of the material, allowing the dyes to be introduced following the rinsing phase.

Should you purchase a slab of this material, then break it, you'll notice that this dyeing process does not go completely through the stone, but is simply a surface type staining.

Although the term is used loosely, "staining" implies that the dye intrudes into the stone a mere fraction of an inch, say .01 each side. Without the acid bath, this would not occur at all.
posted by dammitjim at 11:23 PM on April 12, 2006

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