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[ileney]

I have a couple of questions:

1) I have some Spencer opal and am wondering if anyone has ever tried sugaring the matrix and if that worked? I am guessing not because people seem to make triplets or more rarely small solids from it, but much of my nearly 1 lb. rock is matrix and I can see dots and bits of opal in it, so I wondered, which brings me to...

2) I have a few pale, dull and porous looking opals (that still have nice but sort of diffuse fire) cut by my dad many years ago. They didn't take a polish and really look chalky. I am guessing these are andamooka matrix opals because I don't see what else they could possibly be. Because I can see good fire in them I want to try sugaring them. I am seriously afraid of cooking acid and more dangerous ideas. I could swear I read a slightly less high tech, less scary version of how to do this (maybe using pool muriatic acid outside for the acid part?) Anyone have advice or a link?

[hummingbirdstones]

ileney, I did it once many years ago and don't remember the recipe exactly, but basically what I did was soak the Andamooka sandstone matrix (it was the sandstone matrix I used) in a crock pot with a solution of water and brown sugar in it.  It was a lot of brown sugar, but I don't remember how much anymore.  They cooked in there for something like 10 hours to saturate the matrix as much as possible.  Then I wrapped them tightly in aluminum foil and put them on the gas grill cranked up high for a few hours.  Took them off and put them in a bucket of sand to cool very slowly.

It worked, but not as good as cooking them in acid, which i wasn't going to attempt.  I don't know if this method would work on the gem Andamooka matrix.  I kind of doubt it.

[ileney]

Thanks Robin. That might have been the alternative I heard of. I thought maybe after warming in the sugar solution and drying someone used muriatic pool acid (which maybe is less toxic than sulphuric acid? or are they similar?) and just left it in the sun on a warmish day or something like that, in a glass container inside a plastic one, but maybe I'm not recalling right. I'm very paranoid about the idea of cooking acid.

[hummingbirdstones]

I hadn't heard of the use of muriatic acid.  It's a lot weaker than sulfuric, so I don't know if it will work.  I'm not a chemist, so I'm no help on that end.  I use PH Down as my pickle in a small crock pot, but that's as far as I go with acids.

[rocks2dust]

Muriatic acid is just diluted sulfuric acid, so it would work the same, only take longer.

I'm unsure as to why you'd want to dye the matrix of Spencer opal, however. The rind doesn't take much of a polish. If you are referring to the layers of potch/common opal that are between the layers with play of color, then I'd think both the common and precious layers would both turn black at the same rate, leaving you with a brown or black stone that would hide the play of color.

[gemfeller]

I've used the sugar/acid treatment for Andamooka matrix opal and I've also cut a lot of Spencer material.  My personal feeling is that the Spencer matrix isn't porous enough to absorb the sugar.  That said, I haven't tried it with Spencer so who knows?  I assume you're talking about the T-egg rind of the Spencer nodules, not the opal inside.

[ileney]

Yes I didn’t mean the solid seams. I meant that in the chalky rind of the Spencer opal I sometimes notice bits of opal so I thought maybe it was like Andamooka matrix and only the matrix would turn black, but not the bits.

[VegasJames]

Thanks Robin. That might have been the alternative I heard of. I thought maybe after warming in the sugar solution and drying someone used muriatic pool acid (which maybe is less toxic than sulphuric acid? or are they similar?) and just left it in the sun on a warmish day or something like that, in a glass container inside a plastic one, but maybe I'm not recalling right. I'm very paranoid about the idea of cooking acid.

Muriatic is safer than sulfuric by a long shot but the fumes are highly corrosive to metals.

[VegasJames]

Muriatic acid is just diluted sulfuric acid, so it would work the same, only take longer.

I'm unsure as to why you'd want to dye the matrix of Spencer opal, however. The rind doesn't take much of a polish. If you are referring to the layers of potch/common opal that are between the layers with play of color, then I'd think both the common and precious layers would both turn black at the same rate, leaving you with a brown or black stone that would hide the play of color.

Muriatic acid is hydrochloric acid also sold as pool acid. It is very different from sulfuric.  I work with a lot of different acids all the time, especially hydrochloric. I am particularly careful when it comes to sulfuric or nitric acids.

[rocks2dust]

Muriatic acid is hydrochloric acid also sold as pool acid. It is very different from sulfuric.  I work with a lot of different acids all the time, especially hydrochloric. I am particularly careful when it comes to sulfuric or nitric acids.

Yup, my one functioning brain cell was taking a nap. I should have said hydrochloric, which is what is used to turn the sugar black when dying onyx and opal.

[ileney]

If you think the pool acid thing might work, I think I'll give that a try instead since I have some of that in the shed anyway.

[rocks2dust]

I think muriatic/pool acid can work, but will take a lot longer. Several acids are used in the various darkening recipes. The stone must be allowed to soak in the sugar solution (350g sugar mixed per liter water) for months in order to allow it to soak into the pores of the stone. The acid is used merely to carbonize/blacken the sugar. Results vary, depending on the porosity of the stone. Dye (you could try fabric dye) is an alternative and probably much safer, though perhaps not quite as permanent. There is also the smoking technique (place over a smoky fire to allow soot to penetrate micro pores in the stone) used on opals with similar results. I'm not aware of anyone who has tried any of these on Spencer material.

[hummingbirdstones]

Found this video on YouTube.  This guy uses concentrated sulfuric acid (!!!!):

https://youtu.be/pRXGDrLSTJ0

[gemfeller]

Found this video on YouTube.  This guy uses concentrated sulfuric acid (!!!!):

https://youtu.be/pRXGDrLSTJ0

That's essentially the same process I've used, including sulfuric acid.  The main problems I had were regulating the heat to maintain a constant temp and fume protection.  I used a small sheet of glass to cover the acid container heated on a small hot plate.  Next time I'll use the regulator on my casting burn-out oven.   

One comment:  since the black treatment penetrates only about 1 mm. or less, using the procedure on rough is pointless because the black will be ground away quickly while shaping the cab.  I prepped my cabs to about 600 sanding, treated them, then polished as normal.  Worked very well for me but my matrix wasn't nearly as spectacular as the pieces shown in the vid. 

[hummingbirdstones]

You're a lot braver than I am, Rick!  I think I'd be terrified of the acid and disposing of it.  Can you neutralize sulphuric to get rid of it?

I don't understand why the guy in the video treats stuff before he cuts it into shape, etc.  He obviously knows he's going to have to retreat.  He has quite a few opal videos up and a few more on the Andamooka gem matrix.