Opal Sealant?

Jewelry Discussion
1

I went to a nice gem and rock show recently, and got a small piece
of rock with a thin layer of opal on it that has some really nice
fire (from most angles it glows like a green traffic light, with a
little blue sometimes). I know the layer is too thin to polish, so I
was wondering what might be good to cover it with to use in jewelry.
The dealer mentioned polyurethane? and said he preferred that over
Opticon, but does anyone else have any input on that? I have the
feeling that regular epoxies and such wouldn’t be clear enough for
the sparkle to show through, and I remember someone mentioning that
nail polish is nice and clear but really isn’t anywhere near durable
enough.

Also I’d like to add that if anyone knows somewhere I could just
send the stone to get it sealed, I may rather do that than buying a
gallon of sealant from the hardware store and have nothing else to do
with it after this one project. Thanks in advance for any
:slight_smile:

–Marcy

2 
    I went to a nice gem and rock show recently, and got a small
piece of  rock with a thin layer of opal on it that has some really
nice fire (from most angles it glows like a green traffic light,
with a little blue sometimes). I know the layer is too thin to
polish, so I was wondering what might be good to cover it with to
use in jewelry.

Marcy, it sounds like you got a boulder opal “split”. The opal
forms in thin seams in the ironstone matrix. The cutters will find
a likely seam and cut a chuck of this opal out. Then they will
notch the seam with a diamond saw. Next they split the matrix along
the opal seam using a cold chisel and a hammer. Usually, the rock
will split with an almost even amount of opal on both sides. I have
seen some very nice earring pairs made from these. They end up
being mirror images of each other. Nothing is used to “seal” this
stone. The fractured opal has a surface that almost not polish can
match. Any coating will as you expect, will dull the opal and over
time will usually cloud up to the point of making it worthless.
Just shape it to the outline you want and the thickness you want and
then mount it. They make some very nice stones.

One thing to be careful of though, the ironstone is sometimes not
very strong. Usually, the darker it is, the stronger, the lighter,
the less strong. If you are bezel setting it, use care to have the
bezel fit well and use minimum pressure pulling the bezel down.

Don Rogers

3 
so I was wondering what might be good to cover it with to use in
jewelry.

rankly, I’d not cover it at all. Opal itself is harder than any of
the resins you mentioned. If it’s too thin a layer to polish down,
it should still have the glassy look of a broken glass surface,
unless it’s already been sanded or something. If it is reasonably
shiny from it’s own natural gloss, it needs no additional sealant,
just as a properly cut and polished opan doesn’t need sealant.

The choices you mentioned are, I’d say, poor ones in any case.
Opticon isn’t designed as a surface seal. It’s an epoxy based resin,
used to soak into a stone’s fractures to make them less visible (not
stronger), after which the surface is then sealed with a bit more of
the resin to which hardener has been added. The last step is
actually optional, but prevents “wet” resin from weeping from cracks.
The the cured resin isn’t especially hard, nor a good surface gloss
agent either. In fact, epoxies in general are poor choices, as
they’re a bit yellowish in color, not especially hard, and not
always all that durable over time, though opticon is reasonably
stable.

Nail polish is usually an acrylic. It’s actually not all that bad,
as far as hardness goes, and is as good as other choices you’ve got.
Some of them are actually quite hard for a resin surface. But it may
not be the most attractive, as it tends to go on in a thick layer.

I’d guess your best bet, if you must coat it at all, would be one of
the spray on acrylic plastic coatings, such as Krylon. It’s
colorless, pretty durable, and has a high enough refractive index to
look reasonably bright for a coating.

but none of these are as hard as the opal itself, so Again, I’d
suggest just not coating it at all. If it needs a bit of
brightening, use some cerium oxide powder mixed with water to a
paste, on a small felt wheel, running at low speed (flex shaft or
variable speed dremel on low), and use that to bring up a higher
gloss on the opal layer. Cerium oxide is only a polish, and won’t
remove any thickness to the thin opal layer. it also won’t remove any
but the finest scratches, but if the layer is as thin as you say,
then you might not want to remove such in any case. you can still
get a glossier look right over any small scratches, though they’ll
still show if you look for them…

Hope that helps.
Peter Rowe

4

I have never worked with opals before, but I regularly use Zapon
Lacquer (the best is by Zweihorn/ICI if you can get it) to seal
patina on copper. It looks and acts like nail varnish, but is much
stronger. The other possibility is to cast the piece in clear
polyester resin. You may found that anything you put on the opal
diminishes the shine. Why do you have to cover it at all?