....how does one oil a stone? ...(a person)... had an article
on a lapidary page but I couldn't understand the process ...
Does one vacuum a beaker of oil with the stone in it or do you
use air pressure to force it into the stone?
G’day Dave; my suggestion is to put the flawed stone in a small
vessel together with the warm oil / opticon (or whatever.)
Subject the vessel to as good a vacuum as you can manage. Let
the air in after a few minutes… Repeat the evacuation. etc The
idea is that when you subject the stone to a very low pressure
some of the air in the crack will come out. When the pressure
returns to room value, the pressure of the atmosphere (14.75
pounds/ sq. inch) will force oil into the crack. Repeating this
more than once will help to really fill the crack with oil. Thus
you are subjecting the stone to both vacuum and pressure.
However, the refractive index (light bending power) of the oil
must be as near as possible to that of the stone, otherwise the
crack will be visible.
I used to demonstrate to certain undergraduate classes at a
University. One of the experiments was concerned with refractive
index (RI). I dissolved chloral hydrate in a special liquid,
using a glass rod as a stirrer. As this demonstration was done
using a projector, the students were able to see on the screen
that the glass rod became less and less visible as more of the
chemical was added until the rod completely disappeared when the
refractive indices of the glass rod and the liquid were
identical. Incidentally that solution is used to prepare
specimens for mounting in microscope slides for the same reason.
When transparent gemstones are tested, one method of determining
refractive index is to put them into certain liquids with known
RI values. When the edges of the stone are hard to see, the RI
of the stone and the liquid are very similar. These days it is
done with a refractometer which actually measures the angle to
which the light is bent by the stone. More than you ever wanted to
know about oiling stones! Cheers,
/ / Johnb@ts.co.nz
(_______) In sunny temperate Mapua NZ -