If so, what kinds of cuts do you prefer?
Derek, the nature of Boulder Opal is that the Opal decides the cut.
Most Boulder is in very thin seams that are not necessarily flat.
You end up with some interesting shapes and contours. I
especially like the "splits" which give you a matched pair of what
ever shape they end up.
How many are using the matrix type with color flashes,
The Ironstone Matrix was my first love in opals. Depending on the
opal, it can be an awesome piece or kind of 'Ho Hum'. One thing to
remember with the matrix is that the darker the matrix, the better
the chance of a good finished stone. This is because the lighter
matrix is softer and more porous resulting in a very noticeable
difference between the opal seam and the matrix when polished.
Getting a good polish on the matrix is a trick in its own. You need
to throw out all you knew about cutting and polishing opal. First,
you need to plan on getting dirty. It is nasty stuff to cut as the
Ironstone leaves everything coated with a rusty colored coating. So
don't try to touch up one on your faceting machine that sets on the
coffee table on your white carpet. If you have ever seen a rusty
radiator in a car boil over and leave that rusty brown stain all
over, well that is what you end up with when cutting matrix opal.
Some times it is well worth the mess though.
My mentor in Australia who cuts matrix opal gave me the following
"receipt" for cutting it and getting a good polish.
Rough cut it as any other stone. Start the sanding on 400 grit "DRY"
Progress through 1200 grit still DRY Now go to an expandable drum
with a resin belts and diamond paste starting at 6000 and going
through 50,000. Little water in each step and limit the time in each
step. Let the diamond do its work to eliminate the under cutting.
You can end up with a very good polish and surface using this
method. Just plan on getting dirty and "Please wear a mask" .