STABILIZING PROCEDURE FOR CRUMBLY LAPIDARY ROUGH
Oct 26, 2006 14:42:56 GMT -5
1dave, modstylegems, and 1 more like this
Post by desertdweller on Oct 26, 2006 14:42:56 GMT -5
This is a good method for stabilizing lapidary rough that is porous or crumbly.
Since most stones are cut in water and will probably be subjected to immersion and water-based cleaners, waterglass isn't a satisfactory stabilizer. Various chemical processes can cause silicates to polymerize into opal or agate, as occurs in petrified wood. The hardened silicate from my procedure is clear and colorless. It's not as fast as epoxy, but treated material is "rock-solid" --- no undercutting or discoloration with age. In the end, it's also safer, cleaner and a lot cheaper than Opticon or other epoxies.
Here's the general procedure that seems to be working now. It's not as involved as it may seem at first glance, and gets easier with practice.
1) Clean slabs (or rough less than 1" thick) in a solution of hot water and trisodium phosphate (available in most paint departments for wall cleaning) prepared in the concentration specified for grease removal. I let them soak overnight. This may cause some slight color change - deeper blues and greens on chrysocolla and turquoise. Rinse slabs thoroughly and allow to air-dry.
2) For this step, you need a shallow, lidded stainless steel (not iron or aluminum) pot or pan and a means of holding temperature at around 180 F, substantially below boiling. I found a thrift store electric buffet warming plate which worked nicely. The stabilizing formula is based on sodium silicate solution with a weight ratio of around 3.2 (available at www.chemistrystore.com/sodium_silicate.htm and other similar sources). Read the MSDS! This solution is caustic, and you should wear eye and skin protection to handle it. Spray the pot lid edge with PAM or other cooking spray to keep it from adhering to the pot. Clean up drips and used utensils immediately with warm water. If the solution gets on fabric, rinse and wash it before the silicate dries.
3) Now, this is where things get a little weird... it takes a combination of very low activity organic acid and alkali mineral salts (carbonates, phosphates and sulfates of calcium, potassium, etc.) to get the silicate to polymerize in a non-water-soluble form, e.g. as agate. Though this can be done with very concentrated mineral water (about 1 gallon boiled down to 1 cup) and aspirin or citric acid, I found the easiest and cheapest way to do this was with Emer-Gen-C Lite mineral supplement packets. ***It's important to get the Lite sugar-free version --- sugar or fructose will oxidize and may discolor the stones.*** Dissolve one packet of Emer-gen-C in 1 cup (approx. 250 ml) of water and allow the fizzing to disperse. Add this solution to 8 oz. of sodium silicate in the stainless steel pot and stir to mix. For stones with very fine porosities or hairline cracks, add about 1 teaspoon of liquid dish soap to reduce the viscosity of the solution.
4) Submerge the slabs in silicate solution in a single layer. Stacked slabs may stick together. Cover and let stand on the heat source for at least 24 hours. Longer cooking won't hurt... I've left some material in for up to 4 days. [For very thick material, a pressure cooker has been suggested, but the risks of silicate splash clogging the vent mechanism are too great for my peace of mind.] Remove the slabs and set them on a spray-greased baking rack over newspaper. Allow the slabs to drip dry. The dried slabs are safe to handle bare-handed, and can be gently pried off the rack if they stick. A word of caution --- dried silicate can be as sharp as glass!
5) Place the dry slabs on a cookie sheet and set in a cold oven. Turn the oven to "warm" and leave it on overnight. Turn the oven off and allow the stones to cool to room temperature with the door closed. The slabs should look shiny and any deep cracks will be partially filled. Porous stones should feel noticeably heavier after this treatment. At this point, you can re-clean the stone and "paint" silicate formula to fill larger cracks and voids. Repeat the drying and baking processes to set the added silicate.
The whole cleaning, soaking, drying and baking process can be repeated as many times as you feel necessary. There may be some brownish surface discoloration on the stone, but this comes off with polishing.
Silicate solution can be reused multiple times, adding a little water to replenish the volume. The solution may have some precipitated white silica gel and will turn tea-colored. When a thick layer of silica gel has precipitated and the solution seems thin, treat it by pouring out on about a pound of scoopable cat litter, allowing the litter to dry, then discarding it in regular trash. Don't pour it down the sink.
I've tried to explain in as much detail as I've gleaned from a half dozen or so different trials. So far, it's worked on slabs and rough of many different jaspers, chrysocolla, turquoise, Laguna, Botswana, plume and moss agates, Koroit opal, petrified woods and fossil coral.
Since most stones are cut in water and will probably be subjected to immersion and water-based cleaners, waterglass isn't a satisfactory stabilizer. Various chemical processes can cause silicates to polymerize into opal or agate, as occurs in petrified wood. The hardened silicate from my procedure is clear and colorless. It's not as fast as epoxy, but treated material is "rock-solid" --- no undercutting or discoloration with age. In the end, it's also safer, cleaner and a lot cheaper than Opticon or other epoxies.
Here's the general procedure that seems to be working now. It's not as involved as it may seem at first glance, and gets easier with practice.
1) Clean slabs (or rough less than 1" thick) in a solution of hot water and trisodium phosphate (available in most paint departments for wall cleaning) prepared in the concentration specified for grease removal. I let them soak overnight. This may cause some slight color change - deeper blues and greens on chrysocolla and turquoise. Rinse slabs thoroughly and allow to air-dry.
2) For this step, you need a shallow, lidded stainless steel (not iron or aluminum) pot or pan and a means of holding temperature at around 180 F, substantially below boiling. I found a thrift store electric buffet warming plate which worked nicely. The stabilizing formula is based on sodium silicate solution with a weight ratio of around 3.2 (available at www.chemistrystore.com/sodium_silicate.htm and other similar sources). Read the MSDS! This solution is caustic, and you should wear eye and skin protection to handle it. Spray the pot lid edge with PAM or other cooking spray to keep it from adhering to the pot. Clean up drips and used utensils immediately with warm water. If the solution gets on fabric, rinse and wash it before the silicate dries.
3) Now, this is where things get a little weird... it takes a combination of very low activity organic acid and alkali mineral salts (carbonates, phosphates and sulfates of calcium, potassium, etc.) to get the silicate to polymerize in a non-water-soluble form, e.g. as agate. Though this can be done with very concentrated mineral water (about 1 gallon boiled down to 1 cup) and aspirin or citric acid, I found the easiest and cheapest way to do this was with Emer-Gen-C Lite mineral supplement packets. ***It's important to get the Lite sugar-free version --- sugar or fructose will oxidize and may discolor the stones.*** Dissolve one packet of Emer-gen-C in 1 cup (approx. 250 ml) of water and allow the fizzing to disperse. Add this solution to 8 oz. of sodium silicate in the stainless steel pot and stir to mix. For stones with very fine porosities or hairline cracks, add about 1 teaspoon of liquid dish soap to reduce the viscosity of the solution.
4) Submerge the slabs in silicate solution in a single layer. Stacked slabs may stick together. Cover and let stand on the heat source for at least 24 hours. Longer cooking won't hurt... I've left some material in for up to 4 days. [For very thick material, a pressure cooker has been suggested, but the risks of silicate splash clogging the vent mechanism are too great for my peace of mind.] Remove the slabs and set them on a spray-greased baking rack over newspaper. Allow the slabs to drip dry. The dried slabs are safe to handle bare-handed, and can be gently pried off the rack if they stick. A word of caution --- dried silicate can be as sharp as glass!
5) Place the dry slabs on a cookie sheet and set in a cold oven. Turn the oven to "warm" and leave it on overnight. Turn the oven off and allow the stones to cool to room temperature with the door closed. The slabs should look shiny and any deep cracks will be partially filled. Porous stones should feel noticeably heavier after this treatment. At this point, you can re-clean the stone and "paint" silicate formula to fill larger cracks and voids. Repeat the drying and baking processes to set the added silicate.
The whole cleaning, soaking, drying and baking process can be repeated as many times as you feel necessary. There may be some brownish surface discoloration on the stone, but this comes off with polishing.
Silicate solution can be reused multiple times, adding a little water to replenish the volume. The solution may have some precipitated white silica gel and will turn tea-colored. When a thick layer of silica gel has precipitated and the solution seems thin, treat it by pouring out on about a pound of scoopable cat litter, allowing the litter to dry, then discarding it in regular trash. Don't pour it down the sink.
I've tried to explain in as much detail as I've gleaned from a half dozen or so different trials. So far, it's worked on slabs and rough of many different jaspers, chrysocolla, turquoise, Laguna, Botswana, plume and moss agates, Koroit opal, petrified woods and fossil coral.
