Fire polish thick glass

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  • #10145
    jocko
    Participant

    I have a 20” stainless steel casting ring that I have made several one inch+ in thickness pieces. I use .25” thick stripes to line the ring. when I remove the glass the edges are very rough. I have a small wet belt sander but it takes forever to get is smooth. I would like to make some sinks or just some large thick bowels but I can’t seem to get rid of the squareness of the edges. Before I trash another large piece of glass can anyone tell me if there is a possible fire polish schedule or other way to get the edges rounded without loosing my thickness?

    Thanks

    Mike

    #13351
    Anonymous
    Inactive

    The goal of fire polishing is to heat the skin of the glass enough to smooth it while minimizing the heat that penetrates the glass and allows it to flow/deform.

    Fire polishing a thick piece of glass is difficult.  That’s because the force of gravity on the significant mass means it takes less heating (softening) of the interior to make it deform.  Most thick pieces, when fire polished, come out bulging around the edge.

    When fire polishing thick glass, slowly heat it to the annealing temperature and hold it for as long as you would anneal it.  This ensures that the glass has lost its brittleness and will not thermal shock in the next step, which is to heat as quickly as possible to the fire polish temperture where no hold is required. The faster the kiln can heat between about 900F and 1375F, the less heat that will penetrate the glass and the less it will deform. This is one of the few places that 120V kilns are usually at a disadvantage. Cool the kiln at full speed (or faster by opening it to vent heat) back to the anneal hold temperature. Anneal and cool as required.



    Paul
    FusedGlass.Org
    Helios Kiln Glass Studio
    PaulTarlow.com

     

    #13352
    BeckiWitte
    Participant

    Can large pieces like this be fire polished in a torch ans then annealed in the kiln?

    #13353
    jocko
    Participant

    Blue Carrot

    I will try this weekend so I can be with the kiln. I just took a piece out this morning and it was only about .5 thick so I am going to make another this eve a bit thicker. I will let you know. Thank you for your help

    Mike

    #13354
    jocko
    Participant

    I placed this large piece of glass in the kiln, 150 to 950 held 3 hrs, as fast as poss to 1375 I opened the top un til the temp hit 950 and held for 3 hrs. I kept the thickness but the edges were divitrafied about an inch in. There was a power flash after it hit 950 and I caught it when it was at 750 so I went asap back to 950 held 3 hrs went 300 to 800 held 30min 150 to 100 held 0. I have a large EvenHeat 240vt Any Ideas??

    Thanks

    Mike

    #13355
    wordana
    Participant

    Back to your original problem of rough edges… I assume you are using 1/8″ fiber paper to line your stainless rings?

    Try using Papyros as the first layer of fiber paper that touches the glass. It leaves a very smooth finish that requires much less coldworking than regular, rough fiber paper.

    Papyros is Spectrum’s answer to Bullseye Thinfire — it holds up a lot better than the Thinfire (you can usually remove it from the kiln in one piece, where Thinfire basically turns to powder)

    Dana W.

    Jester’s Baubles Fused Glass Designs

    http://www.jestersbaubles.com

    #13356
    jocko
    Participant

    Thanks, I do use 1/8″, I will try the Papyros. That is what I use on my shelves.

    I need to do some re-wireing this week to get my kiln back online.

    Thanks again and have a great week

    Mike

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