Gavin Stairs on tue 23 jul 02
Gemstones are numerous very different minerals. Some, like diamond, will
be little affected by an ordinary kiln firing. Others, including the
sapphires and emeralds, which are corundum, may change colour. The silica
group can be quite changed, and may partially dissolve. Feldspars will
melt. There are lots which have appreciable water content, and may not
survive. And the carbonates will be lost. There is yet more to worry
about: thermal expansion. Some will crack the ceramic on cooling, while
other will become loose, and may fall out. Proceed with care, and deep pockets
Amethyst is quartz, and may crack the porcelain. Diamonds may crack the
porcelain.
Gavin
At 02:32 AM 23/07/2002, you wrote:
>I have been asked if it is possible to fire gemstones embedded into a =
>porcelain vessel as part of the decorative process. Has anyone any =
>experience or opinion as to how this can safely be achieved without =
>cracking the stones, the vessel, or, even worse, my electric kiln =
>through possible blow out? Any thoughts on the /fragility/stability of, =
>say, amythest in preference to diamond under temperatures of up to 1260 =
>centigrade?
Tommy Humphries on tue 23 jul 02
not a good Idea...most gemstones are single crystals and do not take thermal
expansion well at all. Most would survive without melting, true, but upon
cooling you would have a mess of crazed crystals on your pots. Also many of
the colors would change, or fade completely. I know that tiger eye when
heated to just below red heat will turn red, the iron in the quartz will
oxidize. I have fired quartz crystals up to 4" across to ^6 with no melting,
but the crystals are a solid mass of crazing due to the stress. Opal would
come out looking like the silica in those desiccant bags, as it is a hydrous
gem and would loose all of its water upon heating.
A better solution would be to make some impressions where you want the gems
to be, and set them in place after the pot is fired. I have seen many nice
pots with jewels and cabs on them...there are as many options for mounting
as there are artists working in this area. Some glue the stones directly on
the pot, others will solder findings into holes drilled into the pot for
mounting faceted gemstones.
Good luck!
Tommy
----- Original Message -----
From: "Avril Farley"
To:
Sent: Tuesday, July 23, 2002 1:32 AM
Subject: gemstones and ceramics
I have been asked if it is possible to fire gemstones embedded into a
porcelain vessel as part of the decorative process. Thanks in advance for
any advice.
Avril in the Forest UK
avril@soudley44.freeserve.co.uk
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Avril Farley on tue 23 jul 02
I have been asked if it is possible to fire gemstones embedded into a =
porcelain vessel as part of the decorative process. Has anyone any =
experience or opinion as to how this can safely be achieved without =
cracking the stones, the vessel, or, even worse, my electric kiln =
through possible blow out? Any thoughts on the /fragility/stability of, =
say, amythest in preference to diamond under temperatures of up to 1260 =
centigrade?
Thanks in advance for any advice.
Avril in the Forest UK
avril@soudley44.freeserve.co.uk
BobWicks@AOL.COM on tue 23 jul 02
I taught Jewelry at college level for 25 years and my experience is that you
cannot fire natural gem stones in a kiln because they also have other
ingredients and often melt or explode. This is not the case with man made
gems. I am speaking from my experience of casting molten silver around gem
stones at temperature around 1600 to 1800 degrees F.
Bob
Kathleen Gordon on wed 24 jul 02
Avril-
I have been using Precious Metal Clay of late and it is indeed
possible to fire stones into the clay... i am sure this would also be
true for any LOW fire process..I am not sure about high fire..but as
they say test ,test test..... the gem stones I use are cubic zirconium
which are man made and come through the firing in very good shape...the
literature on natural stones is that they may have some impurities that
might cause them to "explode" or crack in the kiln...if you want to use
them and not fire them you can make a place..considering shrinkage ..for
them..a bezel the jewlery people call it and then glue the stones in
after the fact.....good luck
Michael Banks on wed 24 jul 02
It is hard to generalise here due to the wide range of minerals used as
gemstones. But most are destructively altered by heating to 1260 C, and at
the very least you can expect drastic colour changes. Examples of
deterioration to be expected follow:
Silica minerals can suffer from decrepitation: (become internally shattered)
due to crystallographic inversion e.g: silica minerals (jasper, amethyst,
opal, chrysoprase, citrine, rose quartz, agate, etc) and also feldspars
(moonstone, amazonite etc) -before they melt. This group also usually lose
their colour.
Silica is so prone to decrepitation when heated that this has been used
historically to aid the crushing process of flint. Even minute silica
inclusions in another mineral will render it prone to extreme weakening.
Some gems melt to brown or black glass, e.g: garnet. Others burn away to
nothing in oxidising atmospheres, e.g: diamond. Others lose essential
volitiles and become ash-like, e.g: turquoise, opal, lapis lazuli.
The best survivors will be the most refractory minerals, e.g: zircon, cubic
zirconia and the corundum series (sapphire windows have been used on
heat-resistant spacecraft). But colour changes are to be expected, even with
these.
So, generally most gems are too sensitive to heat to fire them on a pot and
expect them to still look good...
Michael,
in NZ
----- Original Message -----
Avril Farley wrote:
I have been asked if it is possible to fire gemstones embedded into a
porcelain vessel as part of the decorative process. Has anyone any
experience or opinion as to how this can safely be achieved without cracking
the stones, the vessel, or, even worse, my electric kiln through possible
blow out? Any thoughts on the /fragility/stability of, say, amythest in
preference to diamond under temperatures of up to 1260 centigrade?
william schran on wed 24 jul 02
Avril - My students have done lots of experiments embedding stones,
metal, whatnot into raku clay and much success with firing - but gems
in porcelain, hmmm.
Probably have to worry about the porcelain cracking due to amount of
shrinkage. Can't help with gems and high heat.
I'd suggest creating an area to glue/cement the gems into after the firing.
Bill
>I have been asked if it is possible to fire gemstones embedded into
>a porcelain vessel as part of the decorative process. Has anyone
>any experience or opinion as to how this can safely be achieved
>without cracking the stones, the vessel, or, even worse, my electric
>kiln through possible blow out? Any thoughts on the
>/fragility/stability of, say, amythest in preference to diamond
>under temperatures of up to 1260 centigrade?
>
>Thanks in advance for any advice.
>
>Avril in the Forest UK
>avril@soudley44.freeserve.co.uk
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
Fara Shimbo on fri 26 jul 02
Hi Avril and Folks,
Re: gemstones in a pot, I've been firing quartz crystals to cone 9
for years. I embed them in pots when the pots are leather hard
and then glaze. Many times there will be a crack at the glaze line
after the firing's done but this can be sealed with a little super glue.
The quartz comes out just fine, so long as you cool VERY slowly.
I have noticed that while rock quartz is fine in the kiln, amethyst will
turn opaque white. Haven't had enough smoky or rose quartz to be
willing to test a sample, so I don't know how these will work.
Maybe next time I'll try a cubic zirconia, got lots of those.
Fa
--
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Fara Shimbo, Master Crystallière, Certified Public Nuisance
Shimbo Pottery, Box 41, Hygiene, Colorado, USA 80533
www.shimbopottery.com ^^^ www.crystalline-ceramics.info
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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