Glass Casting (Please Help–I’m stuck)

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  • #9073
    Anonymous
    Inactive

    I am just learning glass casting and need some help with problems I have encountered.  My pieces have come out with alot of the plaster stuck to the piece.  It take alot of effort to get the plaster off and the whole piece ends up with a cloudy white appearance–this cloudiness is so bad that you can’t tell the color of the glass. 

    -1-  Can this be caused by silica that is too old?

    -2-  Is there something I can coat the plaster mold with to prevent this?

    The other problem I am having is with the clay that I am using to make my mold.  After my plaster/ silica has set, the clay sticks to the mold.  I guess you can expect a little sticking, but this is so bad that I have to scrape almost the entire inside of the mold to get the clay out.

    -3-  Is there a special clay that you can use to prevent this from happening?    or

    -4-  Is there a release agent to put on the clay to get the sculpted clay to come out of the mold without leaving behind clay?

    Now that I have these piece that are so cloudy, and have clay(that I missed while scraping the mold) baked into the surface of the glass=

    -5-  What can I do to improve the surface of the glass?

    My last problem is that I used too much glass and it ran over the top of the mold.  I used water displacement in order to determine how much glass to use, and I thought I was being very precise, but I ended up with too much glass.

    -6-  What is the best way to determine how much glass to put into the mold?

    I REALLY appreciate any help that anyone can offer to me…I don’t want to continue until I find out what is wrong with my technique.

    Mike

    #11217
    Anonymous
    Inactive

    -1-  Can this be caused by silica that is too old?

    I know that casting plaster has a shelf life (I’ve been told about a year).  I’ve never heard of silica going bad.

    -2-  Is there something I can coat the plaster mold with to prevent this?

    Not coat – but adding 3% alumina hydrate to the plaster silica mix will give you a cleaner release.

    The other problem I am having is with the clay that I am using to make my mold.  After my plaster/ silica has set, the clay sticks to the mold.  I guess you can expect a little sticking, but this is so bad that I have to scrape almost the entire inside of the mold to get the clay out.

    The longer you wait after the plaster sets the more difficult it is to remove the clay. The clay should be removed within a few hours after the plaster sets up.

    -3-  Is there a special clay that you can use to prevent this from happening?    or

    -4-  Is there a release agent to put on the clay to get the sculpted clay to come out of the mold without leaving behind clay?

    A waterpik (the kind people use on their teeth) works well.  You will get soaked though :)

    -5-  What can I do to improve the surface of the glass?

    Try the alumina hydrate – but be aware that most people who cast also coldwork — and there is a reason they call it coldwork.  Depending on the form you can sometimes fire polish.  The trick is to heat the piece slowly past where it can thermal shock and then go as fast as possible to fire polish temp (no hold) and then as fast possible to anneal soak.  It is like trying to wave a hair dryer past a scratched piece of wax to polish the surface but not give the heat a chance to penetrate deeply enough that the piece distorts.

    My last problem is that I used too much glass and it ran over the top of the mold.  I used water displacement in order to determine how much glass to use, and I thought I was being very precise, but I ended up with too much glass.

    -6-  What is the best way to determine how much glass to put into the mold?

    Fill you mold with rice and then pour the rice into a container where you can measure the volume. Then use the fused glass casting calculator on this site to determine the weight of the glass needed to fill the mold.

    Hope this helps,
    Paul



    Paul
    FusedGlass.Org
    Helios Kiln Glass Studio
    PaulTarlow.com

     

    #11218
    michaelhor
    Participant

    Thank you so much for the help–What do you think of using oil based clay and then using purelube to try to get the clay out–ALL the clay out?  I have a new piece to cook and can’t wait to try the rice/volumne method.

    Mike

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