Proper stabilizing of soft stone is an occasional obsession of mine. About the only method I have not tried is hxtal, but I can review a few of my other attempts.
- Epoxy 330 (both tubes) dissolved in 1 pint of acetone. I've tried both letting the stone soak for a week as well as pulling a vacuum with a brake bleeder, both resulted about the same. Epoxy was pulled into fractures, but it didn't soak past the surface in soft areas.
- Sodium Silicate. It's a thick liquid but doesn't dry to a very hard material. It filled cavities and fractures but didn't polish well. I was underwhelmed by the result.
- Hot Stuff. While it appears to penetrate, it doesn't go very deep. I've tried using it for filling small gaps but it undercuts.
...and the winner is...
Opticon! It took a few attempts to figure out the best process, but here's what stabilized some chrysocolla for me. I got an old toaster oven from the Goodwill for five bucks. I poured a thin coat of the resin on the bottom of the toasting pan. Then I placed my chrysocolla slabs on the pan and then painted the top of the slabs with more resin. I then cooked the stones for about an hour on high heat. After turning off the oven and letting the stones cool a bit, I removed each slab and scraped the remaining resin off into the pan. (since the resin hasn't been mixed with the hardner, you can recover most of the resin for future use.) The last step was to mix a small cup of resin with a few drops of hardener. I painted the mixture on both sides of the stone and placed them on a screen to bake under the Arizona sun for a couple days. The result was some very cab-able material. I think the heat expansion does a better job of pulling resin into the stone than any vacuum process could do.