Andamooka Opal Matrix Treating Recipe & Finishing Hints
Andamooka Opal Matrix Stone, is a recognized opal type, not to be confused with other opal matrixes. It is a unique rare opal stone that can be treated. e.g. when pulled from mother earth this opal type is a light base color, it already has the play
of colors and fire within. It is often treated to enhance the visibility of the colors.
This is done by cooking the opal stone in sugar and then carbonizing the sugar,
this turns the sugar black thus giving the stone a dark or black color base backgound.
Please note: generaly there are two types of Andamooka Opal Matrix.
(1) called "Concrete", "Rainbow Opal Matrix" or "Sandstone Opal Matrix"
it is a more porous stone.
the second type (2) is a much Harder Host Stone type, less porous and this type
CAN ONLY BE ACID COOKED as it will EXPLODE if you heat fire it !
TWO STEP Andamooka Opal Matrix Treating Recipe & Guide:
The treating usually penetrates the stone to a depth of about 1/4 inch at best. This penetration can be variable with stones due to the different hardness and porosity of individual stones. With alot of my material I treat larger size rough blocks 1st, then clean a couple of faces to expose the colors. You can then see where the color fires lay better to cut, shape etc. and treat again, this will not hurt the stone.
WHAT YOU WILL NEED (written in blue text below)
2 x electric "Crock Pots" or slow cookers,
One for Sugar Cooking the stones.
The second Crock Pot is for the Acid Cooking of the stones. (see below)
The cookers have a internal sealed heating element & removeable ceramic bowl & lid.
about 2 pounds weight of Brown Sugar.
Approx. 2 liters of industrial grade 99% strength sulphuric acid is required.
The "Rainbow Opal Matrix" can be acid cooked, but better results are gained by heat firing this matrix type. To do heat firing you will need a liquid propane gas (LPG) bottle, cooking burner ring and a cast iron dish with lid.
(see instructions below)
crock pot above / liquid propane gas firing setup below
STEP ONE:
You need to sugar cook the "Rainbow Opal Matrix" or the "Harder Matrix" type first.
My electric cooker ceramic bowls both hold about 3 liters liquid volume capacity each, pour this amount of boiling water into the 1st cooker ceramic bowl and add about 2 pounds of brown sugar and stir until you get it to disolve. Turn the cooker ON to "Keep Warm" or low setting, place your stones into the ceramic cooker bowl and cook for at least 2 days. Then remove the stones, allow them to cool and wipe off any excess sugar syrup from the stones with a dry cloth.
STEP TWO:
Using the other Crock Pot,
Make sure you wear plastic gloves and eye protection as acid spills can burn !
Wash off any spillages immediately if you get it on your skin etc.
Pour about 2 inches depth of acid into the empty ceramic bowl.
Place the stones into the COLD ACID, turn the electric cooker onto low heat setting and leave to cook in the acid all day long, turn off and allow to cool over night. Remove the stones the following morning.
SCOOP THE STONES CAREFULLY OUT FROM THE ACID USING A LARGE METAL KITCHEN LADLE SPOON OR SIMILAR.
Never Put or Drop Water into the Acid, Especially when the Acid is Hot, as it will spit !
Always move the stones too and from the acid when the acid is COLD.
THEN PLACE THE STONES INTO A PLASTIC CONTAINER THAT IS ABOUT 1/2 FULL WITH COOL WATER AND A FEW TABLESPOONS OF BAKING SODA
IT'S ALSO CALLED BI-CARB SODA - IT WILL FIZZ.
YOU BUY IT AT THE GROCERY STORE.
THIS HELPS TO NEUTRALIZE THE ACID -
this mixture is also handy to mop up or neutralize any acid spillages.
FINAL NEUTRALIZING IS DONE BY PLACING THE STONES BACK INTO
THE HOT SUGAR SOLUTION FOR ABOUT 4-5 HOURS.
TAKE OUT, ALLOW TO COOL, THEN RINSE IN WATER.
This 2nd step of the process carbonizes the sugar and gives the matrix stone
its black or darker backgrounding.
Check to see if they have darkened.
IF NOT you will need to sugar cook them & heat fire or acid cook them again.
You can do this many times until you get them darker, this will not hurt the stones.
POLISHED STONES CAN BE RE-TREATED TOO.
If you do not have acid, the Rainbow Opal Matrix can be heat fired to carbonize the sugar. THE HARD MATRIX CAN NOT BE HEAT FIRED.
Place the Rainbow Opal Matrix into the cast iron container, place lid on, light the liquid propane gas (LPG) and allow to heat fire for about 2 hours. Longer or shorter time will not hurt the stones. Turn off the (LPG) ring burner and allow to cool, then check stones to see if they have darkened. If they have not darkened then maybe the cause is not enough sugar in the solution when sugar cooking or the temperature in the cast iron container is not hot enough, or long enough time.
FINISHING HINTS:
The hard matrix can be finished into lovely cabochons for jewelry !
Often this material type rivals Lightning Ridge Opals for bigger Size & Color.
Cut your stone to approx. finished size on the trim saw. Shape your stone on grinding wheels, I quickly knock the rubbish off with the 100grit diamond grinding wheel, then onto the 320grit getting your stone nice and smooth with no sharp edges. Then I use a expander drum with diamond belts. First onto a 600grit, then 3,000 or work through the finer grits. Then final polish using disk with diamond pastes. Or if you don't have the diamond paste, you can still use the conventional method with cerium oxide on a leather buff.
A hint prior to the final polish is to run the dopped stone on a worn out silicon carbide waterproof cloth backed disc (I use a worn out 800/900grit) applying a fair amount of pressure to your stone thus building up some heat on the surface of the matrix stone. These opals have a degree of porosity and this method will help seal and glaze over most of the pores and pits on the face of your cabochon, still use water when doing this or dip the dopped stone into a glass of water every ten seconds or so and feel that it is not too hot before continuing again.
Dopping Tip: I gently heat my stone over the flame of a glass alcohol lamp, with the stone resting in a tablespoon (safe from dropping it !). I also use a drop or two of the following mixture placed on the back of the stone to be dopped, this makes it all stick really well ! A mixture of about 2 teaspoons of Shellac flakes (shellac is french polishing product for polishing wood, you can buy it at the hardware store) mixed with about same amount of metholated spirits until the flakes are dissolved. Heat the stone with a few drops of the shellac mix on and when you notice a slight change with the shellac heating up it should be ready. Then quickly heat your dop stick wax until the wax is about to drip from the dop stick and then attach to your stone. Push the stone firmly into the hot wax moulding the wax to pretty well cover all the back of the stone, therefore it has full support and less likely to break later when you apply pressure when sanding and polishing etc. After you are done, gently heat the wax and use a old thin blade knife or similar to seperate the stone from the wax. To remove any further excess wax from the stone, I place it into a small glass jar containing acetone for 10 minutes or so, then wipe clean with cloth.
RAINBOW OPAL MATRIX will NOT readily polish and needs to be finished with a sealant like opticon or similar to give it a shiny appearance.
If Done Properly the "Hard Opal Matrix" type will take a wonderful mirror like polish.
PLEASE BE CAREFUL ESPECIALY WHEN HANDLING THE ACID
YOU CAN ONLY HEAT FIRE THE "RAINBOW OPAL MATRIX" aka Concrete or Sandstone Matrix.
DO NOT HEAT FIRE THE HARD OPAL MATRIX TYPE - AS DUE TO IT'S HIGH OPAL SILICA CONTENT AND LESS POROSITY IT WILL EXPLODE !
Disclaimer: be careful and do so at your own risk, we accept no liabilities as to what's explained here.