Heart of Stone Studio Blog

Restrictions on firing gemstones in PMC

     My previous posting with Rio Grande's chart on survivability of gemstones when exposed to the heat of a PMC firing has sparked a response from Bridgette Rallo of The Greenwoods Studio. Ms. Rallo is a jeweler, educator, Heart of Stone Studio professional customer, and expert on PMC. She says:

You know, Judy, I really question exactly how the stones they fired at Rio looked after they came out of the kiln...I have never heard of a stone that can survive a firing at the temperatures needed for PMC 3, never mind PMC+ or Standard. The only exception is calibrated hematite, which can take 1100 degrees for 30 minutes. I had an assistant who put a bezel into the kiln without removing a Mexican lace agate and I noticed it after about 5 minutes...the temp had reached 1030 degrees and I was able to salvage the stone but it did darken quite a bit. When Rio says the stone survived, they mean it didn't blow up in the kiln. But I will guarantee you that it had considerable color change. I get color change even on pieces of sea glass, which is why I make pre-fired bezels for them now.

    So, it appears that great care and discretion needs to be practiced when planning to include gemstones in any PMC firing. I am listing some other approaches worth considering:

--Firing only synthetic gemstones and CZs (Cubic Zirconias), although there is no absolute guarantee that these stones won’t change color or at least darken, in the kiln.

--Pressing the gem into plasticine to make a mold, then filling that mold with plaster of paris, popping it out when dry, and then substituting that for the gemstone during firing. After firing, carefully drill or chip out the plaster and you have an automatic seat for the stone. (I suggest drilling a hole through the bottom of the metal seat so that light gets into the stone from the back.) However, unless you’ve set up a bezel or other way to trap the stone in place, you’d have to glue it in, something that you wouldn’t want to do with an expensive stone because it is certain that it would eventually fall out.

--A third option that I’ve thought of but don’t know if it would work with PMC, is to purchase a pre-made prong setting (that fits the stone) and fire the bottom of it right into the clay of the piece, making sure that a bit of clay anchors the setting in permanently. Then you can set your gemstone safely into the setting after firing. Might be worth experimenting with...Any other comments or tips are welcome.

Next posting, my thoughts about the importance of cut in faceted gemstones…

Gemstone suitability for use in PMC

      Now that I have begun to offer melee diamonds and semi-precious colored gemstones on my website, Heart of Stone Studio, people have written to ask which gemstones can be used in firing precious metal clay. Genuine diamonds can, of course, and CZs (cubic zirconias) as well as synthetic stones, but real colored gemstones are another matter. For one thing, if the stone contains any major inclusions that heat and cool at a different rate than the surrounding stone, they can cause the stone to crack or explode. Or, a small fracture, when heated, can expand to become a big, damaging fracture. The other possibility is that the crystalline structure of the gem does not lend itself to firing. Regardless the reason, the result is a double mess--a damaged stone that's also locked in place in your piece.

     So, I called the folks at Rio Grande, a large and reputable jewelry supplier out of Albuquerque, NM. Their research department experimented with firing a variety of different stones in two types of PMC.  I've made up a chart of their findings that I hope the PMC enthusiasts will find useful:

Gem Suitability for Use in PMC	Information provided by Rio Grande
Gemstone	Dry Fire	PMC 3
Chrome Diopside	not available	Survived
Garnet: Almadine	Survived	Survived
Garnet: Pyrope	Survived	Survived
Garnet: Rhodalite	Survived	Survived
Garnet: Tsavorite	not available	Survived
Hematite	not available	Survived
Moonstone	Survived	Survived
Peridot	Survived	Survived
Black Star Sapphire	Survived	Survived
Tourmaline	Survived = iffy	Damaged = iffy
Denim Lapis	Survived = iffy	Damaged = iffy
Lapis Lazuli	Damaged	Damaged
DO NOT TRY THESE STONES
Amethyst
Aquamarine
Black Onyx
Blue Topaz
Blue Misty Chaldecony
Cameo
Carnelian
Citrine
Iolite
Jadeite
Malachite
Mexican Fire Opal
Rhodochrosite
Rose Quartz
Tiger Eye
Turquoise ------------------------------- Any information that PMC experts might like to add would be welcomed.

Evaluating diamonds

      Diamonds are such a mystery to people. They are beautiful, sparkly, extremely expensive, and many people own at least one, yet understanding how the experts assign them value seems to be some sort of inside knowledge that most of us feel excluded from. And, actually, that's somewhat the truth--Certified gemologists, diamond dealers, and jewelry-store owners have their own techniques, their own terminology, their own tests, and we pretty much have to take their word that they know what they're talking about. But then, isn't that true of many professions? That special knowledge is what makes the true insider, and allows one professional to recognize another instantly.

      Well, I'd like to share some insider secrets to help you to understand diamonds. The biggest and best-kept secret is: They may be gorgeous, but they're far from perfect. In fact, if you swept your garage floor and dumped the dustpan contents into a big 55-gallon drum of jello, stirred it up and then chilled it solid, that's pretty much how much of the world's diamond rough would look--filled with bits and pieces of things. Of course, there are those renowned "fabulous finds"--large chunks of clear material, but those are very rare.

     So the bottom line is, the majority of diamonds have "stuff" in them--bits of other material, tiny fractures, discolorations, pieces of diamond crystal grown in a different direction, little chips, etc. etc. This should actually not be surprising, because diamonds are a natural mineral material, and natural material of any type is seldom perfect. That's what makes it natural, after all. Master cutters can cut around the worst stuff, but diamonds are so precious that each and every bit of rough that can be used, is used. The poorest pieces are slated for industrial use, because there, only hardness counts, not clarity or color. But think about it--other than gold and platinum, what materials do you know of where even their dust is valuable?

     OK, this train of thought leads to certain important truths: One is, the larger the diamond, the more difficult it is to find one without any flaws, and the more precious that stone is going to be. Many people dream of getting a flawless diamond, but the reality is, if you could ever afford a truly flawless diamond (flawless inside and out), you could never wear it. It would have to sit forever in the darkness of a bank vault, because one bump of your hand, one tiny nick, and it's no longer flawless. In fact, the few truly flawless large diamonds in existence aren't even set in jewelry. It's too much of a risk. And, to me, the very worst thing about such perfection in diamonds is that it can now be easily duplicated by synthetic diamonds. If they can grow "perfect" diamonds in the lab, I tend to think that detracts from the allure of a flawless genuine diamond.

    The second "secret truth" is that internal flaws (which diamond experts never never call flaws or imperfections; that's too negative, so they call them inclusions), can be, in small amounts, a good thing. You know how on the TV commercials, the snobby diamond expert intones that "no two diamonds are alike," implying that this uniqueness is what adds to their value? Well, you know HOW they can tell that no two diamonds are alike? Yep, by their flaws--sorry, inclusions. If you were to cut the dirty jello in the 55-gallon drum up into ice-cube-sized pieces, every single piece would be unique, too.

    What gemologists do when they inspect a diamond for certification, is take a finished diamond and put it under a microscope. They look at it from the top, the bottom, and the side. On the desk next to the scope they have a drawing of each view of that diamond with all the facets outlined, and they map every single inclusion, every nick, every thing and its exact location in a special code that they mark onto the drawing. They also evaluate its color, and its cut. When they are done, they have noted every single characteristic of that stone in such a way that it's almost like a fingerprint--an absolutely unique picture of that stone. That's important and valuable for two major reasons:

   1. It proves that that diamond is not a synthetic produced in a lab in four days, but a real gemstone produced by mother earth over hundreds of millions of years.

   2. It protects the owner of the diamond. Without a diamond certificate, you have no way of proving that the diamond ring you brought in for resizing still contains those same diamonds when you get the ring back a week later. (That's another reason why, as a buyer, you always want to build a good relationship with a reputable jeweler whom you can trust.)

    So I hope these insights are getting you to think differently about diamonds. More in my next blog. And, just to let you know--I am now selling small, incredibly gorgeous diamonds on my website, Heart of Stone Studio.

      

care and cleaning of drusies

     To effectively clean drusies, it's best to remember what they are--Essentially, they are groups of tiny crystals that grew out of a mineral matrix. Some drusies, like those of azurite, are really crumbly and unstable, which is why I won't sell them on my website. They would fall apart at the slightest touch. Others, like quartz drusies, are both hard and relatively tough, but even then, they're not damage-proof. You have to picture the individual crystals sitting like little teeth in the bone of your jaw--a hard enough knock, or rough abrasion, or lateral pressure back and forth, and that "tooth" can come out of its socket. A few missing crystals, with a dark matrix showing beneath, can detract from the look of a druzy cabochon. That's why proper cleaning and storage is so important.

      First, let's start with coated drusies--titanium, gold, platinum, etc. The coating is very thin--it starts out in vapor form and attaches to the quartz crystals in a vacuum. With proper care, the coating should never wear off. To ensure the full life of a coated druzy, I never put it in a sonic cleaner. Instead, this is how I clean it:

     I make a bath of warm soapy water. I use a dishwashing liquid without any moisturizers in it, something straight like Dawn or even liquid Dial soap. Various jewelry suppliers sell special jeweler's cleaning solution which is also good. I swirl the druzy through the water, or, if it's especially dirty, I let it soak for ten minutes. I don't use brushes on coated stones--the abrasion isn't worth the risk. 

     Next, I rinse in distilled water. Regular tap water has mineral deposits that dull the sparkle of the druzy. If you're doing more than one piece, fill a plastic container with some of the distilled water and place the cleaned drusies in it. Again, you can swirl the stones around or let them sit for several minutes. Try to match the temperature of the soapy water and the rinse water--You don't want to thermal shock the stone by washing it in hot water and plunging it into a cold rinse.

    The next step: Remove the stone and place it right side up on a paper towel, and pat the back and sides of the stone to remove excess water. Don't place the paper towel on the front of the stone because the crystals will snag small fibers from the towel.

     Immediately afterwards, using a hair dryer set on a warm or cool (but not hot) setting, blow dry the stone. I usually hold the stone in one hand and move it around as I hold the dryer in the other hand, rather than trying to dry the stones while they're lying on the paper towel--things blow away that way.

     Clean natural drusies the same way as coated ones. In the case of natural quartz drusies, I get bold enough to use a soft toothbrush and gently brush it across the druzy crystals, especially in areas that might be discolored. Rinse and dry as described above. With other natural drusies, such as pink cobalto calcite and hemimorphite zinc, I refrain from brushing the crystals.

    The cleaning method described above also works for drusies set into finished jewelry. A quick cleaning does wonders to revitalize the sparkle and color in a druzy piece. The only thing you might want to avoid placing into soapy water are pieces containing pearls.

    The safest storage for a piece of jewelry with druzy in it is sequestered from other jewelry pieces that can bump against it. I recommend storing it in a little plastic bag and/or its own storage box.

     Drusies may look delicate, but if cared for properly, most of them are tough enough to last forever in pendants, earrings, bolas, and dressy bracelets that aren't worn often. As always, I recommend that people avoid setting them in heavy-wear items such as rings or belt buckles. You can see drusies in every color of the rainbow on my website: heartofstonestudio.com