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Thread: Cast silver is porous

  1. #1
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    Question Cast silver is porous

    Hi. I'm new to casting so I'm just trying to get up to speed.
    I'm using a Plasticast, A Kaya Cast vacuum system, an electric furnace that has a graphite crucible, and I'm trying to cast sterling silver.
    The cast is coming out porous. Well, that's what it seems to be as I have pitting and jagged holes.
    I've tried a couple of burnout schedules and made sure it's fresh silver, but still get porosity.
    Something I noticed is that even though I've only used the crucible a few times it seems to be degrading and the top of it has pitted and there's a lot of loose graphite powder. I've brushed it off, but could this be getting into the silver?
    Or is there some other possible cause?
    Your help is appreciated.

  2. #2
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    What material are you using for the model ?

  3. #3
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    Default Oops. Should have included that.

    Quote Originally Posted by josef1 View Post
    What material are you using for the model ?
    I'm using Phrozen Wax Like Violet.
    The model is just a plain 3 mm band ring.
    Flask is 3 1/2 x 4 inches
    Schedule is -
    From room temp quickly up to 148 C (298 F). Hold 1.5 hours.
    Ramp over 1.5 hours up to 371 C (700 F). Hold 1.5 hours.
    Ramp over 2 hours up to 732 C (1350 F). Hold 2 hours.
    Ramp down at 300 C (572 F) to casting temp 500 C (932 F). Hold 1 hour before casting.

    EDIT: Something else I should say is that the furnace was at 1030 C (1886 F) which is a fair bit above the melting point of sterling. I understand this is about 890 C (1634 F).
    I also added a pinch of borax and stirred just before casting. I waited a couple of minutes after the stir.
    The vacuum was at max before the pour.


    Last edited by JeffP; 17-08-2022 at 11:25 PM. Reason: To add images

  4. #4
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    How - and how long - have you cured the resin?

  5. #5
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    Your temps seem ok I use 1020-1050 to melt sterling you want it so the metal is spinning , maybe try a carving wax model (Ferris / Kerr wax or equivalent) and see how that casts. If it casts ok which I think it will then I would do a bit of research on casting resins they can be a bit of a pain to get right. Also if you are using a graphite crucible I wouldn't personally use borax as it damages the graphite

  6. #6
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    Quote Originally Posted by ps_bond View Post
    How - and how long - have you cured the resin?
    It was washed by hand, blow dried, and cured in an Anycubic Wash and Cure unit for about 40 minutes.

  7. #7
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    Thanks, everyone. I'm planning on doing a cast of both a resin piece and a wax piece, tomorrow hopefully. I thought if I do them together and the wax one is good then I can narrow it down to the resin one. Not that it will tell me if I've prepared it wrong or not cured it enough.
    The other thing I'll be doing is paying more attention to the sprues. I don't think mine were smooth and consistent enough. Also with the resin model, I'll try and clean it better and polish it if possible.

    And I won't use borax. I was a bit suspicious of that as I found conflicting information on the net.

  8. #8
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    Quote Originally Posted by JeffP View Post
    It was washed by hand, blow dried, and cured in an Anycubic Wash and Cure unit for about 40 minutes.
    Did it go fully white? I've not found the tech specs on the Phrozen resin beyond the burnout cycle; FWIW, I've had reasonable results with Bluecast (and they're pretty hot on giving lots of detail on handling the resin).

    Definitely try the wax - I suspect it's likely to be a curing issue.

  9. #9
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    Quote Originally Posted by ps_bond View Post
    Did it go fully white? I've not found the tech specs on the Phrozen resin beyond the burnout cycle; FWIW, I've had reasonable results with Bluecast (and they're pretty hot on giving lots of detail on handling the resin).

    Definitely try the wax - I suspect it's likely to be a curing issue.
    Nope. The wax remained violet after curing. I've asked them this question but no answer as yet. It was maybe a little darker. Which of the Bluecast resins would you suggest?

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