Best way to Oil Opals?

what’s the best way to oil opals? I have some rough that has cracked,
and would cheerfully disclose the treatment.

ack! don’t oil opals! If they have cracks and you still want to cut
them use opticon and disclose the treatment. Oil or glycerine, I’ve
been told, will make the opals ‘cloudier’ over time, and only mask
the cracks. Opticon will seal them and prevent them from growing.


what's the best way to oil opals? I have some rough that has
cracked, and would cheerfully disclose the treatment. 

The best way to oil opals is to NOT oil opals. All it does is get
them oily. Oiling opals that have become somewhat worn and abraded
may temporarily make the surface scratches less visible, but it
doesn’t fix that, just temporarily hides it. Actual cracks are not
helped at all by oiling, and may even cause discoloration if
impurities or whatever in the oil seeps into the cracks. Oil on opals
is not really a treatment per se, only a means to temporarily delay
any drying out of the stones that is behind the cracking and crazing
that sometimes occurs. And for this, you pretty much need to be
storing the opals immersed in the oil. Once removed a thin layer of
oil no longer protects anything.

The real problem is simply that some opals, especially uncut rough,
is prone to cracking as it sits in air, due to drying out, which
occurs faster at the surface than the interior, causing the surface to
slightly shrink while the interior has not, resulting in surface
cracks. You can’t practically prevent this other than by storing the
opals covered, which is actually best done with just water, not oil.
And it’s only a delaying tactic, not a cure or prevention.

Many people who cut opal simply expect to store it either as rough,
or cut stones, for a while so that those stones which may be prone to
cracking will do their thing and can be weeded out.

Again, the whole thing about oiling opals is that this is a popular,
widely believed by the public, old wives tale with no actual
gemological basis. Just don’t do it. It’s a waste of time, does no
good, and might even cause problems.

Peter Rowe G.G.

Oil will wear off, glycerin is a drying agent and opticon will
eventually feather due to differential thermal expansion and produce
a cloudy crack where before it was just a crack.



Just to follow up, opal is formed by water born silica. Boulder
opal, for example, goes through periods of wet and dry. First the
nodules of ironstone (lateritic sandstone) crack due to a lowering of
the water table. Water born silica fills the cracks then they dry out
again. See my (Queensland Boulder Opal, Gems & Gemology, Spring

At Lightnining Ridge some of the material is mined in wet fields,
that is below the old water table. This opal will crack as it dries.
Cured material has undergone millions of years of slow drying and so
will not crack. Opal of this type will usually crack rather quickly,
within months!


For Information and sample chapters from my new book:

what's the best way to oil opals?

okay, first, you’ve heard the expression “oil and water don’t mix”?
well, opal has water in it - 2% to 22%, depending on the reference
source. you want to stabilize the material, not keep it from getting
wrinkles, so if you have to do something with the cracked rough,
instead of oil use ‘opticon’ according to instructions and the
appearance of some of the cracks should be decreased.

my suggestion, as an opal lover/worker is to use some other, more
stable, rough to avoid any problems with that piece in future.


I have heard that armour oil can be usde with limited success on opal
cracks but I am am also of the belief that once cracked the value is

Steve Bennett