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Degassing Problems with Ceramic Gold

Discussion in 'Metal' started by CaptainInsano25, Sep 14, 2010.

  1. CaptainInsano25
    Notworthy

    CaptainInsano25 Insane Member

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    Hey guys, I'm hoping to get some info on why my ceramic gold is not coming out the color I want it to.
    I use a PenCeram 87-Y gold for my ceramic alloy and when I'm finishing the gold and after sandblasting, it's a beautiful golden color. Yet when I'm degassing in the oven, it comes out dark and reddish. The alloy calls for degassing from 1200-1800F(650-980c). I imagine it is because my degassing temps are too high...?
    Here are the specs of what I'm degassing at:

    Predry/Dry time- 0:00
    Low Temp- 1200F
    Vac Level- High
    Start Vac- 1200F
    Heat Rate- 117
    Vac Release- 1788F
    High Temp- 1800F
    No Hold
    Cool Temp- 1700F

    Any help would be much appreciated,

    Thanks
  2. rkm rdt
    Artistic

    rkm rdt Well-Known Member Donator

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    I finish and sandblast as you do.Then I add the paste opaque and fire. I let the coping degass on the inside of the coping instead.

    Degassing is a complete waste of time.
  3. Gdentallab

    Gdentallab Member

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    the specs are fine, do you hold for 5 min?
    everything is fine , the gold will always have this dark color after degassing.
  4. user name
    Question

    user name Well-Known Member Donator

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    DeGassing is misleading. Used to be, we'd burn off any impurities. With the purity of abrasives and a better understanding of keeping things clean, thats not so much an issue. You do need a slight oxide layer for a good bond with the opaque. Too much ( too dark) and it gets fluffy and the bond gets weak. Since you dont have a hold time, Id back off the high temp untill your oxide lightens alittle.
  5. Wyolab

    Wyolab Member Donator

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    Hey CaptainInsano25! The things we didn't learn in school. I have been using Penceram 40, which is a white precious metal. This doesn't answer your question, but are you finding better aesthetics with yellow gold?
  6. kcdt

    kcdt Well-Known Member

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    Do the instructions call for firing under vacuum? just curious.
  7. charles007

    charles007 Well-Known Member

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    Follow the directions of that alloy... period...the temp, hold time/ vac-no vac changes the color.
    I've got a strict rule I never break, If nothing else works, read the directions.
    Calibrate your oven and call Grant Day at Pentron for help.
  8. CaptainInsano25
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    CaptainInsano25 Insane Member

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    The doc wants HN yellow gold. For me personally, the esthetics don't seem to be an issue either way, it's a longevity issue I think.

    As for other replies; I haven't ever done a hold time as it specifically says in the instructions this about degassing, and nothing else:
    "DEGAS: 1200-1800F with vacuum no hold"

    I'm going to degas today, I'll let you know how it works out.
  9. Wyolab

    Wyolab Member Donator

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    Let's hope nobody is around to suffer when you degas. And turn on a fan. haha.
  10. Alex/plus

    Alex/plus New Member

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    Well Captain, here's my old method.

    I use Dedeco "Goldies" crosscut burs to finish the surface and clean in distilled water then fire to mfg's directions. After I cool the little charcoal jewels I do the crosscut method again with distilled bath and fire again.

    You will find your oxide layer will be just right and you have eliminated any chance of contaminates on your high nobel substrate. I have used this method for thirty years with no bubbles or shadows.

    I never go near the blaster unless the case is near finished and I'm making the crowns interiors look nice....and I haven't "degassed" for over forty years, I oxide.

    Just something to ponder.......Alex
  11. dmonwaxa

    dmonwaxa Moderator

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    Well if you have not degassed in 40 years you must be really full of it. :D just kidding. You are right in that we oxidize rather than degass.years ago when stones were used to prepare the surface for ceramic the procedure would burn off impurities that led to gassing. Today with the use of carbides we don't have that problem provided the burs are clean and sharp. The purpose of degassing is to create some oxide on the surface of the metal to enhance the opaque bond.
  12. Mark Jackson

    Mark Jackson New Member

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    Charles my man, you make me proud to be a dental technician,

    One thing I didn't see spoken about was the need to add AT LEAST 50% new alloy to every casting. During casting, there are certain trace elements that are lost, and need to be reconstitued with fresh alloy. With repeated casting of a button, you can alter the chemistry of the alloy, and therefore will observe hevaior you might not not be what you expect, even if you follow the instructions of degassing exactly.
  13. dmonwaxa

    dmonwaxa Moderator

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    Yes, 50% new alloy should be used. Oxide is your friend to establish the initial bond in the PFM process. Usually produced from traces of Sn (tin) In (indium), they all but vaporize if superheated in the melt. Ruthenium used to control grain size and formation when depleted due to remelts causes the alloy to become brittle and gassy due to the incomplete formation of grain structure in alloys. Over oxidizing of alloys or the stripping of porcelain will lead to poor bond stength.

    In a PFM bond the oxides of the alloy and the metal oxides in the opaques fuses together through heat.

    This interface is most critical for the fusion of the ceramic material and requires 3 types of bonds; what are they.? Noobies only,,,

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