The green wax is great for subtractive carving but it seems to
bubble and change its properties when I have used it with a wax pen
to make additions to a carving. So my questions are (keeping in
mind that I am looking to preserve the hardness and detail
capabilities of green jeweler's wax):
I assume you're talking about the hard, plasticized carving waxes
such as "file-a-wax" that are intended for machining or working with
burs and files, etc.
One of the things about these waxes (there are a number of forms.
The green is the hardest/stiffest. You might also try the purple
medium hard, or the blue, which is softest) is that they are slow to
crystalize. When you initially melt them with a wax pen, or melted
and poured into a mold, they will be softer, almost a bit gummy and
weak. Seams will break, and they won't carve as well, despite being
solidified. You CAN work them right away, if you adjust for this
change, but you can also fix it by letting it stand. The next day,
you'll find it's finished solidifying and crystalizing enough so it's
mostly back to it's original feel and workability. Sometimes, just a
few hours is enough.
I've used the purple grade of wax quite a bit with several types of
molds. These waxes don't inject especially well into detailed molds
because they tend to not fill details too well, and then have
noticable shrinkage. But I use molds made to produce ring blanks.
They were once sold by GIA, and an open top pressure injector fills
these molds, which are made of acrylic with aluminum cores, quite
well. The initial injections are a bit soft, but by next day or
more, they might as well have been sawed out of the original block.
Whether you get bubbles depends a lot on whether you're overheating
the wax. Try not to get it any hotter than needed to melt it. The
occasional bubble doesn't matter so long as it's imbedded within the
model. If it comes to the surface, a wax pen fixes them.
The other side of this answer is that these waxes were really
intended for subtractive methods like machining or filing/carving,
not working with hot tools.
You can, as you found, use both methods, but these waxes are not
ideal for that.
But the waxes intended for hot tool use have their own drawbacks,
such as generally being a lot more fragile or gummy, etc.
Hope that helps