Sometimes it is necessary to stabilize rocks before cutting
and polishing them. Stones with
fractures, porous stones or brittle stones will benefit from stabilization,
allowing you to cut and shape them without risking the loss of the stone. Typically, I hear of three primary methods of
stabilizing stones. I will summarize
these methods below. Then, I would like
to introduce you to a material that is used by museums to stabilize fossils and
artifacts. This material, butvar, is a
polyvinyl acetate and is used by museums because it does not deteriorate even
after very long periods of time and it does not discolor. It has an added advantage that it can be
mixed to any consistency desired, so you can make a thin penetrant or a thick
glue with it. I have used this material
to stabilize stones before cabbing them with success.
Typical methods of stabilizing stones
1.
Backing:
A backing is applied to stones, most commonly turquoise and opal, in
order to keep the stone “natural” while holding the fragile material together. Backing is simply applying a thin layer of
material to the back of the stone that will help hold the stone together. This mostly helps porous stones stay together
and helps to keep stones together that have fractures. Backing material varies widely. Sometimes, a thin piece of stone is adhered
to the stone. Then the stone is cut and
polished as normal. Backing is not used
if the back of the stone may be visible in the finished product. Backing materials include basanite, black
jade (typically a dark stone), or synthetic materials. Devcon epoxy, an epoxy with metal in it, is
sometimes used. JB Weld, another metal
epoxy, is also common. A thin layer of
the epoxy is applied and allowed to dry completely before the stone is cut and
polished.
2.
Thin
cyanoacrylate (“super glue): Thin super
glue can be applied to a stone with fractures or pits. The superglue will fill the fractures and
pits, holding them together. While this
method may work for fractures and pits, I have not had luck with using it to
stabilize a generally fragile stone.
Most often the glue just forms a coating on the surface of the stone,
which easily peels off during the cutting process.
3.
Epoxy
Resin
Opticon resin: I have
heard mixed results about this material.
Some people swear by it, others hate it.
Opticon is a thin resin that is supposed to dry water clear, so it does
not discolor the stone. It can be used
to impregnate a porous stone, so it fills a niche the first two methods do
not. It can be a little tricky to
use. For a description of using Opticon,
see these instructions on the mindat website:
https://www.mindat.org/article.php/1129/Methods+to+Stabilize+Material+for+Cutting
Standard epoxy:
I found reference to using epoxy dissolved in acetone on this discussion
board: http://forum.rocktumblinghobby.com/thread/15452/stabilizing-procedure-crumbly-lapidary-rough?page=2#ixzz4xrfEbGnn. Note that I read elsewhere that it says to
use equal parts of epoxy and acetone.
Butvar Polyvinyl Acetate
There are a few different types of butvar that have different
molecular weights. The two most common
are B-72 and B-98. I have used both of
these in my museum work. Typically we
used B-72 in fossils that were rather wet, but mostly we used B-98. B-72 can be dissolved in alcohol or
acetone. B-98 should be dissolved in
acetone. Note: Please use caution with these materials. They are not toxic and they will not hurt
your skin, but the acetone can. The
acetone is a known carcinogen and it is recommended that you wear gloves and
eye protection when working with it. Do
not get it in your eye – you will glue your contact to your eye and it will
scratch the surface of your cornea (sure, ask me how I know!!). For the most part though it is very
safe. We use is all the time on fossils
in the field and the lab. I will mention
a couple of different methods for using butvar to stabilize your rocks.
1. Mix a thin consistency of acetone and butvar
in a container that has a lid. There
should be enough butvar in the container so that it will actually work, but it
should still be water thin. So add
butvar, and if it starts getting thick, add a little more acetone to thin it
back out. The amounts are not
critical. You will want a large enough
container and enough of the mixture to cover the stone you are working with. Put the stone in the container. Let it sit for several days, 4-7 is
recommended. During this time, It is
advised to shake or stir the
container. I found shaking most useful
in order to stir the stone around in the container. One option, which I have not done, but I plan
to try at some point, is to put the stone in a container where you can add
suction to it. I am thinking like a
space bag, where you put things in the bag then use a vacuum to suction
it. If you do this, you would want to
apply suction to pull the butvar solution up, but NOT suck it completely out of
the container. Repeat this several
times. The advantage of doing this is
that it will force the butvar into the stone and there will be less wait
time.
2. What I found to be most efficient was to
create a thin concentration of butvar in the acetone, it needs to be pretty
thin the penetrate the rock. Then I put
the rock on a piece of plastic wrap and pour the butvar over it (this is the
method we use in the field, especially when the bone is still in the rock and
we can’t soak it). I will do this, let
the acetone evaporate, and continue doing this until is does not evaporate
within about 10-15 seconds. Then I know
the butvar has penetrated as much as it can.
I turn the rock over and repeat on the other side. Then I let it dry for a few hours. I did not find it necessary, but it was
suggested that if you heat the stone before applying the butvar it well help to
open the spaces.
I have a new material I collected from North Carolina, which I
call Mountain Petronella. It has very
soft minerals mixed with hard minerals and they have a lot of planes of
weakness in them. I was not able to cab
this material but when I stabilized it with butvar, it cabbed great.
Mountain Petronella from North Carolina |
I also have a piece of granular peridot, which has individual
grains that are very loose. I was able
to stabilize and cab this material as well.
Granular Peridot |
I have turquoise i need to stabilize..and have used epoxy 330..but am going to try butvar. Any specific recipes for the mix of butvar too acetone? I know you say there is no specific mix...but i dont want to ruin this batch. What would be a good ratio please.
ReplyDeleteKindly,
Jeremiah
Jeremiah.urbas@yahoo.com
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