Peter, I can accept what you are saying here. I think
however the reason that there may seem to be enough shrinkage
for it to impact the setting is that as opal is such a soft
material, and wearing away of the surface of the stone is so
common, that perhaps this is what is happening and being
perceived as "shrinkage".
Um. Opal is still about five in hardness. Fragile, yes. But
not really softer than, say, glass. Things don’t wear down
without something to do the wearing down. Even with normal wear
and tear in a ring, most opals get scratched up and dinged, but
their dimensions don’t actually change. And in this case, we’re
not talking about a situation where there was any wear and tear
occurring, other than the mild scrubbing that occured in the
washing process. this isn’t going to to anything to the
dimensions due to abrasion. Even extremely soft stones (and
opal, while soft relative to major stones, isn’t actually all
THAT soft.) require some substantial abrasion of some sort to
change the surface dimension, and when that happens, even before
you change dimensions, you’ve destroyed the polish/surface finish
of the stone… Another thing to keep in mind with regard to
this thread is that the original suggestion was that the opal
expanded due to water absorption… clearly no type of abrasion
would do that…
Something to remember , Peter, is that glass flows and you don’t
need heat to start it flowing. Gravity alone will accomplish that
task with only gravity as a master. Check out old glass with a
wavy appearance. It wasn’t made that way originally. It takes
many years (decades in fact) but it does it in the end. The best
way to tell if it is that old is to check both the side where it
is wave and the side where it seems smoother. There should be a
substantial difference in thickness. Thicker near where the
bottom was. Paul
Beg to differ, just a bit. Yes, glass is technically a super
viscous liquid. But under normal conditions of normal temperature
and gravity, it doesn’t flow enough to significantly change shape
or sag. That takes significantly elevated temperatures. Modern
made sheet glass is so smooth because of the method of
manufacture. Called float glass, it is literally formed by
being poured out onto a surface of liquid metal. That surface
must be level, and when the glass flows out, it too levels,
prducing a highly uniform and smooth sheet of glass. Old glass
was not made this way, but was, if you go back far enough,
actually hand blown. Pioneer age windows were made by blowing a
bubble, and opening up the top, just as is often done when making
glass hollow ware (vases, etc.). That is then spun to open it up
into a shallow platter shape, and eventually a disk. In the
hands of a good glass blower, these disks can be several feet
across, and quite surprisingly uniform (Look at the large Dale
Chihuly works, if you’re unconvinced of the sizes attainable)
Early windows might be from small enough disks the punty mark
might even be on the window. later factory made ones were large
enough that the only artifact left is curved ripples in the
glass. Later still, some glass was produced by rolling it, but
until the development of the float process, this wasn’t so
uniform. The glass in older buildings is often this way.
Consider: If glass flowed in only decades, we would not be
likely to have quite so many examples of perfectly preserved
ancient glass, from roman times and as much as a thousand years
earlier. Most of this old glass is highly oxidized, but it
hasn’t sagged significantly. Note that I say significantly.
Some of them have moved a bit. My main disagrement with the
original statement is the word decades. I’d have said
centuries. Usually, many of them. But I should note that here,
I’m on shakier ground than with metals. Only took a couple glass
blowing courses back in art school… So I might be wrong. If
so, well… it happens…
Still a rookie. I’ve only been at it about 18 years. One thing
that really busts my chops is chlorine.
Ladies who lounge at the pool all summer with their chains on.
The chain just falls apart around Sept. Oh, the horror. I
soaked a friends heirloom ring in a mild HCl solution overnight
just to loosen up the acreted muck. The next morning the ring
literaly crumbled to flakes. Tears were shed and a friendship
was strained. I would not get chlorine any where my jewelry for
any reason.
I’m rarely confident but all the esoteric reactions with the
sugaring and such probably taake a back seat to chlorine
corrosion.
As a poor rank amateur. I wish to set an opal on a silver larger backing for a pendant. Should I prong it or bezel it or both. Want to protect it. Help please.
While a bezel might result in slightly more protection, it would be easy to crack an opal while bezel setting. If you are really a rank amateur, cutting four oversized prongs out of a sheet and setting the opal on a sheet that is larger than the outside diameter of the opal would probably be easiest and most risk free. Both the Practical Metalsmith (McCreight) and Sharr Choate’s book should have a picture of this kind of setting, and they are available at many public libraries. If you are really a wuss, you can pull the prongs down close, but not touching and apply a small amount of CA glue right under the prong where it is almost in contact with the stone, but I hesitate to mention such a bastardized procedure on this august forum.
Do yourself a favor and use pure silver if you choose to go with a bezel
setting. It’s a dream to work with!
If you want to use prongs, do not use pure silver but work with a silver
alloy and anneal it dead soft.
Don’t set the opal to tied in a setting but “close it in” leaving a very
small gap.
Compare it with a mother holding her baby. She’s not squizing her child but
holding it secure leaving it space to breathe.
To clarify, gold is not affected by chlorine. Its alloys are. Copper is the main one.
NEVER introduce chlorides to gold alloys, they will ruin all your good work. It sounds like you were grasping at straws in order to find a solution to the opal issue.
Stop guessing as to what has occurred, and how to resolve it.
You took many steps before your brought this forward.
Ask someone who has been in the trenches before you experiment on items belonging to others. advice is available here.
I have to agree with everyone that mentioned the bleach. Chlorine on karat gold is a huge no no. It doesn’t take that long and the effects are cumulative.
